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The structures and energetics of species with the stoichiometries (Me2CNO)M(CO)nCp (M = Cr, Mo, W; n = 3, 2, 1; Cp = η5-C5H5) have been studied by density functional theory. The experimental structure Mo2-1S with an NO-dihapto Me2CNO ligand found by X-ray crystallography for (Me2CNO)Mo(CO)2Cp is shown to be the lowest energy isomer by a substantial margin. The expected initial Me2CNOMo(CO)3Cp product from the reaction of NaMo(CO)3Cp with Me2C(NO)Br used to synthesize (Me2CNO)Mo(CO)2Cp is predicted to undergo facile CO dissociation based on ΔH and ΔG values. The energetics of the currently unknown analogous chromium and tungsten systems appear to be similar to that of the molybdenum system. The structures Me2NC(CO)OM(CO)2Cp (M = Cr, Mo, W) with a dimethylcarbamate ligand are much lower energy (Me2CNO)M(CO)3Cp isomers but are clearly not accessible from reactions of the anions CpM(CO)3− with Me2C(NO)Br. The lowest energy structures for the monocarbonyl (Me2CNO)M(CO)Cp are of the type (Me2C＝N)M(O)(CO)Cp with separate dimethylimino and oxo ligands formed by oxidative addition of the Me2CNO unit to the central metal atom. [ABSTRACT FROM AUTHOR]

The first‐row transition metal 1‐norbornyl derivatives CpM(nor) Cp = η5‐C5H5; nor = 1‐norbornyl; M = Ti to Cu), including the experimentally known CpNi(nor) reported by Lehmkuhl and Dimitrov, have been examined by density functional theory and benchmarked by the more accurate DLPNO‐CCSD(T) method. The lowest energy CpM(nor) structures for the later first row transition metals from manganese to copper are found to be high‐spin state structures in which the 1‐norbornyl ligand is bonded to the metal only through the M–C σ‐bond to the bridgehead carbon atom. The favored spin states range from doublet for CpCu(nor) to sextet for CpMn(nor). The pattern of favorable structure types changes for the CpM(nor) derivatives of the earlier first row transition metals to the left of manganese since all of their low energy structures have singly or doubly agostic 1‐norbornyl groups. The agostic C–H–M interactions in the CpM(nor) derivatives are characterized by their reduced density gradients and low ν(C–H) frequencies. [ABSTRACT FROM AUTHOR]

The thiophosphoryl complexes (PS)M(CO)n (M from V to Co) and their corresponding dimers with P2S2 ligands have been studied at the DLPNO-CCSD(T)/cc-pVTZ//M06L/cc-pVTZ level of theory. For the mononuclear complexes containing the highly bent 1-e donor PS group with ∠SPM angles of ∼115°, the (SP)V(CO)6 and (SP)Co(CO)4 complexes are energetically disfavored and (SP)Mn(CO)5 is only slightly favored towards CO loss. The (SP)Cr(CO)5 and (SP)Fe(CO)4 complexes with a bent 2-e donor PS group with ∠SPM angles of ∼133° are both thermodynamically and kinetically disfavored towards dimerization. Similarly all of the (SP)M(CO)n (M from V to Co) complexes with linear 3-e donor PS ligands are energetically disfavored towards dimerization, excepting for Mn(CO)4(PS). The trans-influence of PS follows the sequence 3-e NO ≥ PS (linear) > CS > PS (2-e bent) ≈ CO. [ABSTRACT FROM AUTHOR]

Binuclear manganese complexes with covalent Mn–Mn bonds include dimanganese carbonyl complexes and dimanganese non-carbonyl complexes with bidentate anionic ligands. Density functional theory (DFT) using the M06-L functional is used to study some known dimanganese complexes and three series of model paddlewheel-type dimanganese complexes M2Lx and M2Lx·2H2O (L = HNCHNH, HNC(NH2)NH and OCHO respectively; x = 2, 3, 4). The DFT results for model structures for known dimanganese complexes agree well with the experimental structures and lead to predictions of ground state spin multiplicities. For the model paddlewheel-type complexes, predictions are made with regard to ground state spin multiplicities, and Mn–Mn bond lengths. Formal bond orders (fBO) from 0.5 to 4.5 for all the Mn–Mn bonds are assigned by electron counting. Molecular orbital analysis yields Mn–Mn bond orders (BO) matching the fBO values. Four "super-short" Mn–Mn bonds (lengths 1.618 to 1.639 Å) are found in higher energy isomers, along with other short Mn–Mn quadruple bonds. The effects of axial ligation by two H2O ligands are also noted. The Mn–Mn bond lengths are categorized into distinct ranges as per the Mn–Mn fBO values from 0.5 to 4.5, ranges which are compared with other experimental and computational estimates. [ABSTRACT FROM AUTHOR]

The experimentally known cobalt ethylenedithiolate complex CpCoS2C2H2 as well as its rhodium and iridium analogues are aromatic systems that can function as pentahapto six-electron donor metallodithiolene ligands by binding through all five atoms of its CoS2C2 ring. The lowest energy CpMS2C2H2·Cr(CO)n (n = 3, 2) and CpMS2C2H2·Fe(CO)2 structures (M = Co, Rh, Ir) by substantial margins are predicted by density functional theory to have structures with such pentahapto η5-(CpMS2C2H2) (M = Co, Rh, Ir) ligands. The CpMS2C2H2·Cr(CO)3 structures appear to be favorable as indicated by high carbonyl dissociation free energies (ΔG) exceeding 15 kcal mol−1. The lowest energy structures for the carbonyl-richer CpMS2C2H2·Cr(CO)4 and CpMS2C2H2·Fe(CO)3 systems have trihapto CpMS2C2H2 ligands involving a heterometallic metal–metal bond and two metal–sulfur bonds retaining an uncomplexed C＝C double bond in the ethylenedithiolate ligands. The CpMS2C2H2·Fe(CO)3 structures can be derived from the structures of the long-known (RS)2Fe2(CO)6 derivatives by replacing one of the Fe(CO)3 units by an isoelectronic/isolobal CpM unit. Such CpMS2C2H2·Fe(CO)3 structures appear to be favorable as indicated by high carbonyl dissociation free energies (ΔG) exceeding 15 kcal mol−1. Higher energy CpMS2C2H2·Cr(CO)4 and CpMS2C2H2·Fe(CO)3 structures involve coordination of the C＝C double bond and at least one sulfur atom of the CpMS2C2H2 ligand to the chromium or iron atom but have long metal–metal distances suggesting lack of a direct heterometallic metal–metal bond. In the lowest energy structures of the still carbonyl richer CpMS2C2H2·Cr(CO)5 and CpMS2C2H2·Fe(CO)4 the CpMS2C2H2 ligand is a dihapto ligand that is bonded to the chromium or iron atom through a heterometallic M–M′ (M′ = Cr, Fe) bond and a metal–sulfur bond. Other types of dihapto ligand–metal bonding found in higher energy CpMS2C2H2·Cr(CO)5 and CpMS2C2H2·Fe(CO)4 structures include bonding only the C＝C double bond of the ethylenedithiolate ligand to the chromium or iron atom as in a simple (olefin)M(CO)n complex or bonding of adjacent carbon and sulfur atoms in the CpMS2C2H2 ligand to the chromium or iron atom. The latter mode of dihapto C,S bonding of the CpMS2C2H2 ligand can be interpreted as a π-bond from a C＝S double bond in the dithioglyoxal structure for CpMS2C2H2. [ABSTRACT FROM AUTHOR]

The geometries and energetics of the binuclear fluoroborylene manganese carbonyls Mn2(BF)2(CO)n (n = 8, 7, 6) have been investigated using density functional theory. Coupling of two fluoroborylene ligands to give a bridging difluorodiborene μ-B2F2 ligand with a relatively long ∼1.9 Å B–B bond has been observed in two of the three lowest energy Mn2(BF)2(CO)7 structures as well as the lowest energy Mn2(BF)2(CO)6 structure. Higher energy Mn2(BF)2(CO)6 structures have two separate bridging BF groups and short Mn≡Mn distances of ∼2.3 Å suggesting the formal triple bond required by the 18-electron rule. [ABSTRACT FROM AUTHOR]

The structures and energetics of the acenaphthylene iron carbonyl complexes (C12H8)Fe(CO)n (n = 4, 3, 2), (C12H8)Fe2(CO)n (n = 8, 7, 6, 5, 4), and (C12H8)Fe3(CO)n (n = 9, 8), including the known (η2-C12H8)Fe(CO)4 and (η5,η3-C12H8)Fe2(CO)5, have been examined using density functional theory. The two experimentally known (η5,η3-C12H8)Fe2(CO)5 structures, related by a thermally reversible photochemical haptotropic rearrangement, lie within ∼1 kcal mol−1 from each other in energy and more than 20 kcal mol−1 below any other (C12H8)Fe2(CO)5 isomers. Decarbonylation of the pentacarbonyl to the tetracarbonyl (C12H8)Fe2(CO)4 is predicted to retain the formal Fe–Fe single bond but to convert one of the CO groups to a four-electron donor bridging η2-μ-CO group. The lowest-energy carbonyl-rich (C12H8)Fe2(CO)n (n = 8, 7, 6) structures lack direct iron–iron bonds and have the ligand hapticities expected from the 18-electron rule. The low CO dissociation energy of ∼5 kcal mol−1 for (C12H8)Fe2(CO)6 suggests that these carbonyl-rich species are not viable. The addition of an Fe(CO)3 moiety to the binuclear (C12H8)Fe2(CO)n (n = 6, 5) complexes to give the trinuclear (C12H8)Fe3(CO)n (n = 9, 8) complexes, respectively, is predicted to be exothermic by ∼50 kcal mol−1. These trinuclear complexes have pentahapto–bis(trihapto) acenaphthylene ligands with an Fe–Fe bond in the octacarbonyl structures. The experimental mononuclear (η2-C12H8)Fe(CO)4 structure with a dihapto acenaphthylene ligand is the lowest energy isomer. The hapticity of the acenaphthylene ligand increases from dihapto to pentahapto or hexahapto upon CO loss to give (C12H8)Fe(CO)n (n = 3, 2). [ABSTRACT FROM AUTHOR]

Open metallocenes containing a metal sandwiched between two U-shaped pentadienyl or substituted pentadienyl ligands have been synthesized by Ernst and co-workers using reactions of pentadienyl or substituted pentadienyl anion reagents with metal halides. The complete series of such open metallocenes (2,4-Me2C5H5)2M of the first row transition metals (M = Ti to Ni) has now been examined using density functional theory. The experimentally known lowest energy structures of the early transition metals are open metallocene structures with two pentahapto U-shaped η5-2,4-Me2C5H5 ligands. Such structures can exist as syn-eclipsed, gauche-eclipsed, and/or anti-eclipsed conformations of similar energies. The theoretical predictions of the lowest energy conformations of the open metallocenes are in excellent agreement with available experimental data. Singlet and triplet spin state structures are preferred energetically for the Ti and Cr derivatives, respectively. For (η5-2,4-Me2C5H5)2V, doublet and quartet spin state structures are spaced in energy by 7.6 kcal mol−1. The (2,4-Me2C5H5)2Mn energy surface is complicated with doublet, quartet, and sextet spin state structures closely spaced in energy. In the sextet spin state of (2,4-Me2C5H5)2Mn only the end carbon atoms of the 2,4-Me2C5H5 ligand are within bonding distance of the manganese atom. This corresponds to tetrahedral C4Mn coordination similar to that found experimentally in the sextet ground state t-butyl derivative (2,4-tBu2C5H5)2Mn as well as the related Mn(CN)42−. The low energy structures for the “open ferrocene” (η5-2,4-Me2C5H5)2Fe are singlet spin state structures with two U-shaped pentahapto η5-2,4-Me2C5H5 ligands but otherwise analogous to ferrocene. The low energy (2,4-Me2C5H5)2M structures of the late transition metals Co and Ni have at least one trihapto η3-2,4-Me2C5H5 ligand. The lowest energy (2,4-Me2C5H5)2Ni structure is a singlet spin state structure with two trihapto η3-2,4-Me2C5H5 ligands and a 16-electron nickel environment analogous to the well-known bisallylnickel, (η3-C3H5)2Ni. [ABSTRACT FROM AUTHOR]

Theoretical studies are reported on methylphosphepine, methylbenzophosphepine, their norcaradiene isomers, and their metal complexes with Fe(CO)3 and CpCo (Cp = η5-C5H5) units. Both methylphosphepine and methylphosphanorcaradiene are C6H6PCH3 species existing as anti/syn stereoisomer pairs with the methylphosphepine structures at slightly higher energies. The transition states for the interconversion of these isomers and their benzo derivatives lie ∼20 kcal mol−1 in energy above the methylphosphanorcaradiene isomers. Complexation of either C6H6PCH3 ligand with the transition metal units Fe(CO)3 and CoCp leads to energetically closely spaced η4-tetrahapto and η3-trihapto isomers of the methylphosphepine complexes and η4-tetrahapto isomers of the methylphosphanorcaradiene complexes. However, the bis(dihapto) (η2,2-C6H6PCH3)Fe(CO)3 and (η2,2-C6H6PCH3)CoCp complexes involving coordination of non-adjacent C=C double bonds lie at significantly higher energies. Fusion of a benzene ring to the C6H6PCH3 rings in methylphosphepine and methylphosphanorcaradiene leads to significantly different structures of their lowest energy metal complexes. Thus the lowest energy (C10H8PCH3)Fe(CO)3 and (C10H8PCH3)CoCp structures are η2,2 and η4 methylbenzophosphepine complexes, which avoid using any carbon atoms of the benzene ring in the ligand for metal complexation. Higher energy (C10H8PCH3)Fe(CO)3 and (C10H8PCH3)CoCp structures have tetrahapto ligands with one or both C=C double bonds of the benzene ring complexed with the metal atom. [ABSTRACT FROM AUTHOR]

The experimental realization of pentagonal prismatic structures for M@(M = Co, Fe) containing interstitial transition metal atoms makes of interest the chemistry of corresponding manganese derivatives Mn@. The neutral Mn@Ge10may be regarded as a complex of a polyhedralligand with an interstitial Mn in the +2 oxidation state. However, the lowest energy Mn@Ge10structure with the expected sextet spin state for high-spin d5Mn(II) lies ~23 kcal mol−1in energy above the lowest energy isomer thereby suggesting that such germanium polyhedra function as strong field ligands for encapsulated transition metals. The lowest energy structures for the Mn@anions (z = −1 to −5) are all centered pentagonal prisms. Higher energy Mn@structures have outer Ge10polyhedra based on the tetracapped trigonal prism similar to the lowest energy Co@structure and on the bicapped square antiprism similar to the B10deltahedron. Other Mn@structures have outer Ge10polyhedra with four or five quadrilateral faces as well as six or eight triangular faces, respectively. Bioctahedral (Ge5)2Mn5−structures were also found for the pentaanion with a manganese vertex common to two MnGe5octahedra. The cationic species Mn@was found to have a more complicated potential surface than the anions. Tetracapped trigonal prismatic and bicapped square antiprismatic structures as well as a variety of more open structures were found for Mn@. [ABSTRACT FROM AUTHOR]

The cyclopentadienyliron trifluorophosphine hydride CpFe(PF3)2H, in contrast to CpFe(CO)2H, is a stable compound that can be synthesized by reacting Fe(PF3)5 with cyclopentadiene. Theoretical studies on the binuclear Cp2Fe2(PF3)n (n = 5, 4, 3, 2) derivatives derived from CpFe(PF3)2H indicate the absence of viable structures having PF3 ligands bridging Fe–Fe bonds solely through the phosphorus atom. This contrasts with the analogous Cp2Fe2(CO)n systems for which the lowest energy structures have two (for n = 4 and 2) or three (for n = 3) CO groups bridging an iron–iron bond. Higher energy singlet Cp2Fe2(PF3)3 structures have a novel four-electron donor bridging η2-μ-PF3 ligand bonded to one iron atom through its phosphorus atom and to the other iron atom through a fluorine atom. Other higher energy triplet and singlet Cp2Fe2(PF3)2 structures are of the Cp2Fe2F2(μ-PF2)2 type having terminal fluorine atoms and bridging μ-PF2 ligands. The lowest energy Cp2Fe2(PF3)5 structure is actually Cp2Fe2(PF3)3(PF4)(μ-PF2) with a bridging PF2 group and a terminal PF4 group. Such structures are derived from a Cp2Fe2(PF3)4(μ-PF3) precursor by migration of a fluorine atom from the bridging PF3 group to a terminal PF3 group with a low activation energy barrier. [ABSTRACT FROM AUTHOR]

Theoretical studies predict the lowest energy structures of the binuclear cyclopentadienylrhenium hydrides CpReH (Cp = η-CH; n = 4, 6, 8) to have a central doubly bridged Re(μ-H) unit with terminal η-Cp rings and the remaining hydrides as terminal ligands. However, the lowest energy CpReH structure by more than 12 kcal mol has one terminal η-Cp ring, a bridging η,η-Cp ring, and two terminal hydride ligands bonded to the same Re atom. The lowest energy hydride-free CpRe structure is a perpendicular structure with two bridging η,η-Cp rings. The previously predicted bent singlet CpRe structure with terminal η-Cp rings and a formal Re-Re sextuple bond lies ∼37 kcal mol above this lowest energy (η,η-Cp)Re structure. The thermochemistry of the CpReH and CpReH systems is consistent with the reported synthesis of the permethylated derivatives Cp*ReH and Cp*ReH (Cp* = η-MeC) as very stable compounds. Additionally, natural bond orbital analysis, atoms-in-molecules and overlap population density-of-state in AOMIX were applied to present the existence of rhenium-rhenium multiple bonds. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The lowest energy Fe2(CO)n(CE)2 structures (E = S, Se, Te; n = 8, 7, 6) do not have separate CE ligands but instead have coupled C2E2 ligands functioning as four to six electron donors to the pair of iron atoms. The exothermicity of such coupling reactions as a function of the chalcogen E increases in the sequence S ＜ Se ＜ Te. However, the monomers Fe(CO)4(CE) are stable species owing to the high activation energies for the coupling reactions. Thus, the thiocarbonyl Fe(CO)4(CS) is a stable experimentally known complex. However, the coupled Fe2(CO)7(C2E2) structures are preferred both thermodynamically and kinetically over isomeric Fe2(CO)7(CE)2 structures with discrete CE ligands. For the CS ligand, the previously optimized lowest energy Fe2(CO)n(CS)2 structures (n = 7, 6) with discrete CS ligands are now found to lie ∼11 kcal mol−1 (n = 7) and ∼30 kcal mol−1 (n = 6) in energy above the lowest energy isomeric Fe2(CO)n(C2S2) structures with coupled C2E2 ligands. [ABSTRACT FROM AUTHOR]

Trimethylenemethane (TMM) has long been known as a ligand in metal carbonyl complexes such as [η4-(CH2)3C]Fe(CO)3 and [η4-(CH2)3C]Cr(CO)4. The prospects for synthesizing currently unknown TMM complexes of cobalt carbonyl have been explored by a density functional theory study of the binuclear complexes [(CH2)3C]2Co2(CO)n (n = 2, 3, 4, 5, 6). The dicarbonyl is unexpectedly found to favor by more than ∼12 kcal mol−1 a perpendicular structure [μ-(CH2)3C]2Co2(CO)2 with bridging η4-TMM ligands, terminal CO groups, and a relatively short Co–Co distance of ∼2.29 Å. This is the first example of an energetically favorable perpendicular binuclear metal complex structure having bridging acyclic hydrocarbon ligands. The other viable species is [(CH2)3C]2Co2(CO)4, which is a substitution product of the well-known Co2(CO)8 with terminal η4-TMM ligands. Similar to Co2(CO)8, doubly bridged and unbridged [(CH2)3C]2Co2(CO)4 structures have approximately equal energies within ∼2 kcal mol−1 and predicted Co–Co distances of ∼2.5 and ∼2.7 Å, respectively. Carbonyl-rich [(CH2)3C]2Co2(CO)n (n = 5, 6) structures are also found with dihapto η2-TMM ligands. However, these are predicted to be unstable with respect to CO dissociation to give [(CH2)3C]2Co2(CO)4. [ABSTRACT FROM AUTHOR]

A previous theoretical study on Cp2M2B n −2H n −2 (Cp=η5-C5H5; M=Ru, Os; n =8–12) derivatives indicated a general energetic preference for structures having M–M distances of 2.7–2.9Å with corresponding WBIs of 0.3–0.4 suggesting surface metal–metal single bonds. Replacing the two CpM units in these structures with a single PnM2 unit (Pn=η5, η5-C8H6) leads to different types of PnM2B n −2H n −2 (M=Ru, Os; n =8–12) structures having significantly shorter M M distances of 2.5–2.7Å with corresponding higher WBIs of 0.5–0.7 suggesting surface metal–metal double bonds. The lowest energy such structures have central M2B n −2 bisdisphenoids, tricapped trigonal prisms, and edge-bridged tricapped trigonal prisms for the 8-, 9-, and 10-vertex systems, respectively. The lowest energy 11-vertex PnM2B9H9 structures are based on the most spherical 11-vertex deltahedron, which can be either a closo or isocloso polyhedron. The lowest energy 12-vertex PnM2B10H10 structures are based on an “isoisocloso” 12-vertex deltahedron with two degree 6 vertices. However, icosahedral PnM2B10H10 structures with surface M M triple bonds are also energetically accessible. [ABSTRACT FROM AUTHOR]

The oblate deltahedral structures for the experimentally known 2n− 4 Wadean skeletal electron systems Cp2Re2Bn−2Hn−2 (Cp = η5-R5C5 ligand; R = H, CH3; n = 8 to 12) differ radically from the more nearly spherical 2n skeletal electron isocloso deltahedra such as the known Cp2Fe2C2Bn−4Hn−2 and 2n + 2 skeletal electron closo systems such as the extensive series of known Cp2Co2C2Bn−4Hn−2 derivatives. Density functional theory has now been used to investigate the intermediate “missing” systems, namely the 2n− 2 Wadean skeletal electron systems Cp2M2Bn−2Hn−2 (M = Ru, Os). The lowest energy such structures are predicted to have central deltahedra with n− 1 or n− 2 vertices capped by the remaining BH vertices. This generates larger deltahedra having one or two degree 3 vertices leading to tetrahedral cavities. In all of the lowest energy Cp2M2Bn−2Hn−2 structures the metal atoms are located at the highest degree vertices, most frequently degree 6 vertices. These metal vertices share a deltahedral edge with M–M distances ranging from 2.7 to 2.9 Å and Wiberg bond indices of ∼0.3 to ∼0.4. The structural pattern changes drastically for the 12-vertex systems Cp2M2B10H10 (M = Ru, Os) where the lowest energy structures are “isoisocloso” deltahedra having two adjacent degree 6 vertices for the metal atoms as well as eight degree 5 and two degree 4 vertices. Higher energy Cp2M2B10H10 structures are based on a regular icosahedron with all degree 5 vertices having unusually short M≡M edges of ∼2.2 to ∼2.3 Å with corresponding high Wiberg bond indices of ∼1.3 to ∼1.5 suggesting formal metal–metal triple bonds. [ABSTRACT FROM AUTHOR]

The bis(heptalene)dimetal complexes (CH)M of the first row transition metals from Ti to Ni are predicted by density functional theory to exhibit 'submarine' sandwich structures with a pair of metal atoms sandwiched between the two heptalene rings. For the early transition metal derivatives (CH)M (M = V, Cr) there are two types of such structures. In one structural type the metals are sandwiched between two heptahapto heptalene rings with metal-metal distances (3.5-3.8 Å) too long for direct metal-metal bonding. The other type of (CH)M (M = V, Cr, Mn) structure has a pair of bonded metal atoms sandwiched between a fully bonded heptalene ligand and a heptalene ligand bonded to the metals only through an eight-carbon heptafulvene subunit, leaving an uncomplexed cis-1,3-diene unit. The formal metal-metal bond orders in these latter structures are 3, 2, and 1 for M = V, Cr, and Mn with predicted bond lengths of 2.5, 2.7, and 2.8 Å, respectively. For (CH)Fe a singlet structure with each iron atom sandwiched between a hexahapto and a tetrahapto heptalene ring is energetically preferred over an alternate structure with ferrocene-like iron atoms sandwiched between two pentahapto heptalene rings. Partial bonding of each heptalene ring to the metal atoms occurs in the late transition metal derivatives (CH)M (M = Co, Ni). This leads to an unsymmetrical structure for the cobalt derivative and a structure for the nickel derivative with each nickel atom sandwiched between a trihapto ligand and a tetrahapto ligand. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Binuclear palladium complexes of planar hydrocarbon ligands are of particular interest since both the coaxial structure (η5-Me5C5)2Pd2(μ-CO)2 and the perpendicular structure (μ-C6H6)2Pd2(Al2Cl7)2 have been synthesized as stable compounds. Here we report theoretical studies on a family of related compounds. For the formal Pd(ii) derivatives Cp2Pd2X2 (Cp = η5-C5H5; X = F, Cl, CN) the perpendicular structures with direct Pd–Pd bonds are predicted to lie in energy below the isomeric coaxial structures. These coaxial structures have long Pd…Pd distances indicating the absence of palladium–palladium bonds. The lowest energy perpendicular Cp2Pd2X2 structures (X = F, CN) and a higher energy similar Cp2Pd2Cl2 structure contain a substituted η4-C5H5X cyclopentadiene ligand obtained by the addition of X to one of the Cp ligands. For the formal Pd(i) complexes Cp2Pd2L2 (L = CO and CS) the coaxial structures lie in energy below the isomeric perpendicular structures with a particularly large energy separation of ∼19 kcal mol−1 for the thiocarbonyl derivatives. However, for Cp2Pd2(CNCH3)2 the coaxial and perpendicular isomers have essentially the same energies. [ABSTRACT FROM AUTHOR]

The recent (2010) synthesis of the boronylplatinum halide (R3P)2Pt(BO)Br by Braunschweig and coworkers makes interesting the chemistry of metal carbonyl boronyls isoelectronic with the binary metal carbonyls Mx(CO)y. In this connection, theoretical studies on Fe2(BO)2(CO)8 isoelectronic with the known Mn2(CO)10 predict symmetrical unbridged structures consisting of Fe(BO)(CO)4 units linked by an iron–iron single bond of ∼2.9 Å length. These Fe2(BO)2(CO)8 structures with a staggered arrangement of the BO and CO ligands are similar to the experimental structure of Mn2(CO)10. Three such structures are found within ∼3 kcal mol−1 of energy differing only in the locations of the terminal BO groups. Related higher energy unbridged eclipsed Fe2(BO)2(CO)8 structures are found with small imaginary vibrational frequencies of around 30i cm−1. Following the corresponding normal modes leads to the corresponding staggered structures. Even higher energy symmetrical Fe2(μ-CO)2(BO)2(CO)8 structures are found with two bridging carbonyl groups lying 15 to 21 kcal mol−1 above the global minimum, again similar to the isoelectronic Mn2(CO)10 system. In addition to the above structures higher energy unsymmetrical Fe2(BO)2(CO)8 structures are found, which have no analogues in Mn2(CO)10 chemistry. These include structures in which an Fe(CO)4 unit is connected to an Fe(BO)(CO)4 unit through a bridging BO group without an iron–iron bond as well as a structure in which an Fe(CO)5 unit is connected to an Fe(BO)2(CO)3 unit by an Fe–Fe dative bond. The lowest energy Fe2(BO)2(CO)8 structure is viable towards symmetric dissociation into two Fe(BO)(CO)4 radicals as well as unsymmetrical dissociation into Fe(CO)5 + Fe(BO)2(CO)3 with dissociation energies in excess of 15 kcal mol−1. [ABSTRACT FROM AUTHOR]

Theoretical studies show that pendant dimethylamino groups can play a significant role in the chemistry of unsaturated binuclear dimethylaminoborole iron carbonyls. For [CHBN(CH)]Fe(CO), the lowest energy structures have single CO bridges and Fe-Fe single bonds of lengths ~2.8 Å. The lowest energy [CHBN(CH)]Fe(CO) ( n = 4, 3) structures have two bridging CO groups with Fe=Fe double bonds of lengths ~2.5 Å for n = 4 and three bridging CO groups with Fe≡Fe triple bonds of lengths ~2.2 Å for n = 3. These structures are similar to structures previously found for the corresponding methylborole derivatives (CHBCH)Fe(CO). However, slightly higher energy [CHBN(CH)]Fe(CO ) ( n = 4, 3) structures are found in which dimethylaminoborole is a six-electron donor bridging ligand using electron pairs from the nitrogen atom as well as from the two C=C double bonds. For the more highly unsaturated [CHBN(CH)]Fe(CO ) ( n = 2, 1), low energy singlet ( n = 2) and triplet ( n = 1) perpendicular structures are also found with similar bridging six-electron donor dimethylaminoborole ligands. In addition, highly unsaturated [CHBN(CH)]Fe(CO ) ( n = 3, 2, 1) structures are found with agostic hydrogen atoms bridging an iron-carbon bond. [ABSTRACT FROM AUTHOR]

The known butadiene-iron carbonyl derivatives (η4-C4H6)Fe(CO)3, (η2-C4H6)Fe(CO)4, and (η2,2-C4H6)[Fe(CO)4]2are potential precursors to binuclear derivatives of the type (C4H6)2Fe2(CO)nrelated to the known cyclobutadiene derivative (η4-C4H4)2Fe2(μ-CO)3. In this, density functional theory predicts viable structures with tetrahapto C4H6ligands as well as one, two, and three bridging carbonyl groups and formal Fe–Fe single bonds, FeFe double bonds, and FeFe triple bonds, respectively, for (C4H6)2Fe2(CO)5, (C4H6)2Fe2(CO)4, and (C4H6)2Fe2(CO)3. The tetracarbonyl (C4H6)2Fe2(CO)4is predicted to be unfavorable with respect to disproportionation into (C4H6)2Fe2(CO)5+ (C4H6)2Fe2(CO)3. The carbonyl-richer binuclear derivatives (C4H6)2Fe2(CO)6and (C4H6)2Fe2(CO)7are predicted to have structures having one or two dihapto η2-C4H6ligands, respectively, in addition to formal Fe–Fe single bonds. However, these carbonyl-rich structures are predicted to dissociate into mononuclear (η2-C4H6)Fe(CO)4and (η4-C4H6)Fe(CO)3fragments. Natural bond order (NBO) analysis is used to explore qualitative electronic structure considerations. [ABSTRACT FROM AUTHOR]

The report (2009) of an unusual and unexpected Fe3(μ3-BF)2(μ-BF)(CO)9structure, an isoelectronic fluoroborylene analogue of the long known Fe3(CO)12, makes of interest the structures of the unsaturated Fe3(BF)3(CO)8isoelectronic with Fe3(CO)11. In this connection, seven singlet and eight triplet structures are found for Fe3(BF)3(CO)8within 30 kcal/mol in energy of the global minimum. Natural bond orbital (NBO) analysis aids in the understanding of the electronic structure of these systems. None of the predicted structures has even a single terminal BF group. In the three lowest energy singlet Fe3(BF)3(CO)8structures two of the BF groups are face-semibridging ligands whereas the third BF group is a simple edge-bridging ligand. The face-semibridging BF groups in these structures are joined to the Fe3triangle with two short Fe–B bonds of ∼2.0 Å and one long Fe–B bond of 2.4 Å. A fourth singlet Fe3(B3F3)(CO)7(η2-μ-CO) structure, lying only ∼7 kcal/mol above the lowest energy singlet structure, has a central Fe3B3capped tetrahedron analogous to the central Os6bicapped tetrahedron in the long-known isoelectronic Os6(CO)18. This last cluster suggests the potential accessibility of fluoroborane metal carbonyl clusters having deltahedral structures related to those found in the deltahedral boranes. [ABSTRACT FROM AUTHOR]

Transition metal complexes with bridging PF3 groups are unknown analogous to metal carbonyls with bridging carbonyl groups. The possibility of bridging PF3 groups in binuclear Co2(PF3)n complexes (n = 9, 8, 7, 6, 5) and the tetranuclear Co4(PF3)12 has now been investigated by density functional theory (DFT). The lowest energy Co2(PF3)8, Co2(PF3)7, and Co4(PF3)12 structures are predicted to be unbridged structures with cobalt-cobalt bond distances of ∼2.8 Å, ∼2.5 Å, and ∼2.6 Å, respectively. The lowest energy Co2(PF3)6 structure is an unsymmetrical unbridged structure with a Co-Co distance of ∼2.5 Å. For the more highly unsaturated Co2(PF3)5 both triplet and singlet structures are found, consisting of two Co(PF3)2 units linked by two bridges, namely a PF2 group and a F atom. Such Co2(PF3)5 structures have square planar cobalt coordination and a Co...Co distance too long for direct bonding. In addition, a singlet Co2(PF3)5 structure is found, with two semi-bridging PF3 groups and a very short Co ··· Co distance of ∼2.1 Å indicative of the formal quadruple bond required to give both cobalt atoms the favoured 18-electron configuration. Bridging PF3 groups with no cobalt-cobalt bond are found in a high energy structure of Co2(PF3)7 and in a Co2(PF3)9 structure unstable with respect to PF3 loss to give Co2(PF3)8. The dissociation of Co2(PF3)8 into two Co(PF3)4 radicals is predicted to be only slightly endothermic at -14.3 kcal/mol (B3LYP) or 7.1 kcal/mol (BP86). However, in contrast to its carbonyl analogue Co4(CO)12, the dissociation of Co4(PF3)12 into 2 Co2(PF3)6 is highly exothermic. Optimization of the structure of the experimentally known but not structurally characterized bis(difluorophosphido) derivative Co2(PF3)6(µ-PF2)2 predicts the expected structure with a long Co ··· Co distance of ∼3.5 Å indicating the lack of a direct cobalt-cobalt bond. DFT predicts tetrahedral structures for Co(PF3)4 and HCo(PF3)3 as well as the experimentally known trigonal bipyramidal structure for HCo(PF3)4. [ABSTRACT FROM AUTHOR]

Abstract: Relationships have been observed between the metal formal oxidation state and the metal valence electron counts in closo/isocloso and nido/isonido pairs of polyhedral metallaboranes. In general, the metal formal oxidation state increases by two units in a closo → isocloso or nido → isonido structural transformation, generally involving diamond–square–diamond processes relating to internal metal oxidative addition reactions. More exotic “isoiso” structures are found for metallaboranes containing metals exhibiting relatively high oxidation states such as molybdenum, tungsten, and rhenium. The free borane ligand obtained by removal of the metal vertex from a metallaborane structure can be classified as symmetric or asymmetric depending upon the nature of the metal–ligand bond. In symmetric borane ligands found in closo metallaboranes, the metallaborane structure is generated by symmetrical “centroid” metal capping of the ligand open face. However, in asymmetric borane ligands found in nido metallaboranes, the metallaborane structure is generated by skew-symmetrical or offset metal capping of the ligand open face. Capping regime descriptors are defined to describe these types of metal–borane bonding. In addition, electrostructural correlation tables are described for closo/nido and nido/arachno pairs relating metal formal oxidation states, the numbers of metal valence electrons, and the capping regime descriptors. [Copyright &y& Elsevier]

B3LYP/DZP(Lanl2dz) study of Fe(CO)n(CE)2 (E = S, Se, Te; n = 4, 3) suggests that the Fe(η2-E–C) structures are energetically preferred for singlet Fe(CO)4(C2E2) and triplet Fe(CO)3(C2E2). The tendency for coupling reactions of CE ligands to form C2E2 ligands by carbon–carbon bond formation increases in the sequence S ＜ Se ＜ Te. [ABSTRACT FROM AUTHOR]

The Cp 2 Fe 2 (vegiMe)(CO) n (n = 3, 2, 1) complexes of the chelating biscarbene vegiMe ligand have been investigated by density functional theory. Triplet and quintet Cp 2 Fe 2 (vegiMe)(CO) n (n = 2, 1) structures have similar energies to their singlet isomers relating to the relatively weak field biscarbene ligand. [Display omitted] • The Cp 2 Fe 2 (vegiMe)(CO) n (n = 3, 2, 1) complexes of the weak field rigid dicarbene vegiMe have been investigated by DFT. • The tricarbonyls Cp 2 Fe 2 (vegiMe)(CO) 3 are disfavored relative to CO dissociation. • Dicarbonyl structures have the vegiMe ligand bridging an Fe-Fe σ bond. • Triplet and quintet Cp 2 Fe 2 (vegiMe)(CO) n (n = 2, 1) structures have comparable energies to singlet structures. Binuclear cyclopentadienyliron carbonyl derivatives of the weak-field rigid chelating bidentate dicarbene vegiMe ligand with a tricyclic backbone are shown by theoretical studies on the Cp 2 Fe 2 (vegiMe)(CO) n (n = 3, 2, 1) systems to have higher spin triplet and quintet structures of comparable energies to isomeric singlet structures satisfying the 18-electron rule. Thus triplet structures of the tricarbonyl Cp 2 Fe 2 (vegiMe)(CO) 3 with the vegiMe ligand as a bidentate chelate to a single iron atom are of comparable energies to singlet isomers with no iron-iron bond and the vegiMe ligand bridging the two iron atoms. Similarly, triplet and quintet structures for the dicarbonyl Cp 2 Fe 2 (vegiMe)(CO) 2 are of comparable energies to singlet structures with Fe–Fe single bonds that are substitution products of the well-known Cp 2 Fe 2 (CO) 2 (µ-CO) 2. The only low-energy singlet structure for the monocarbonyl Cp 2 Fe 2 (vegiMe)(CO) has an unusual six-electron donor bridging vegiMe ligand forming not only the usual two C(carbene)→Fe dative bonds but also a N→Fe dative bond. The other low-energy Cp 2 Fe 2 (vegiMe)(CO) structures are various types of triplet and quintet spin state structures. [ABSTRACT FROM AUTHOR]

The stability of the experimentally known complex (Et3P)2Ir(CO)(Cl)(F)(SF3) of the third row transition metal iridium suggests that SF3 complexes of the third row transition metals might be viable species in contrast to the SF3 complexes of the first row transition metals previously studied by theoretical methods. However, the metal complexes [M](SF3) ([M] = Ta(CO)5, Re(CO)4, CpW(CO)2, CpOs(CO), and CpPt) containing three-electron donor tetrahedral SF3 ligands are thermodynamically disfavored relative to the isomeric [M](SF2)(F) derivatives with predicted energy differences ranging from -19 to -44 kcal/mol. The one exception is an Ir(SF3)(CO)3 isomer containing a one-electron donor pseudo-square-pyramidal SF3 ligand having essentially the same energy as the lowest energy Ir(SF2)(F)(CO)3 isomer. This, as well as the stability of the known (Et3P)2Ir(CO)(Cl)(F)(SF3), suggests that metal complexes containing one-electron donor pseudo-square-pyramidal SF3 ligands might be viable synthetic objectives in contrast to those containing three-electron donor tetrahedral SF3 ligands. The [M](SF2)(F) derivatives formed by sulfur-to-metal fluorine migration from isomeric [M](SF3) complexes are predicted to be viable toward SF2 dissociation to give the corresponding [M](F) derivatives. This suggests the possibility of synthesizing metal complexes of the difluorosulfane (SF2) ligand via the corresponding metal trifluorosulfane complexes with the SF3+ cation as the ultimate source of the SF2 ligand. Such a synthetic approach bypasses the need for the very unstable SF2 as a synthetic reagent. [ABSTRACT FROM AUTHOR]

Buchalski and co-workers showed in2008 that reactions of the nickelafluorenylanion CpNiC12H8–with MX2(M = Co, Ni) give the dinickelametallocene sandwich compounds(CpNiC12H8)2M. We now report theoretical studies on the related bis(nickelacyclopentadienyl)metalderivatives (CpNiC4H4)2M and bis(nickelaindenyl)metalderivatives (CpNiC8H6)2M as wellas the bis(nickelafluorenyl)metal derivatives. The structures of thelowest energy bis(nickelacyclopentadienyl) sandwich compounds (CpNiC4H4)2M may be derived from those of thecorresponding metallocenes Cp2M by replacing a CH groupin each Cp ring with an isolobal CpNi unit. The Ni–M distancesof ∼2.5 Å indicate formal single bonds and thus a pentahaptoη5-CpNiC4H4ligand. The spinstates of the lowest energy (CpNiC4H4)2M derivatives are similar to those of the corresponding metallocenesCp2M, namely, singlet, doublet, and triplet for M = Fe,Co, and Ni, respectively. Fusion of benzene rings to the nickelacyclopentadienylrings to give first the bis(nickelaindene) sandwich compounds (CpNiC8H6)2M and then the experimentally knownbis(nickelafluorene) sandwich compounds (CpNiC12H8)2M lowers the energy of the higher spin state. As a result,the lowest energy (CpNiC12H8)2Costructure is not the doublet spin state of Cp2Co and (CpNiC4H4)2Co but instead a quartet spin state.This is in accord with experimental work showing (CpNiC12H8)2Co to have a magnetic moment of ∼3.7μB, indicating three unpaired electrons and thusthe predicted quartet spin state. [ABSTRACT FROM AUTHOR]

Abstract: The recent synthesis by Vidović and Aldridge of the complex (η 5-C5H5)2Ru2(CO)4(μ-BF) containing the fluoroborylene ligand (BF), isoelectronic with CO, suggests the possibility of introducing the BF ligand into binuclear cobalt carbonyl derivatives of the type Co2(BF)2(CO) n (n =7, 6, 5, 4, 3). This has now been explored using density functional theory. Structures in which both BF groups bridge a cobalt–cobalt bond are energetically preferred for the Co2(BF)2(CO) n (n =6, 5, 4, 3) derivatives over other types of structures. Thus the Co2(μ-BF)2(CO)6 structure with two bridging BF groups lies more than 18kcal/mol below the next lowest Co2(BF)2(CO)6 structure and appears to be a reasonable synthetic objective. This differs from the well-known isoelectronic Co2(CO)8 for which the structures with two bridging CO groups and with all terminal CO groups are so close in energy that they are found experimentally to exist in equilibrium. Examples of Co2(B2F2)(CO) n (n =7, 4, 3) derivatives are found in which the two BF groups have coupled to form a bridging difluorodiborene (B2F2) ligand with a B–B distance of ∼1.9Å. However, the Co2(B2F2)(CO)7 structures do not appear to be viable since loss of a CO group to give Co2(BF)2(CO)6 is predicted to be an exothermic process. [Copyright &y& Elsevier]

Abstract: The qualitative aspects of the chemistry of the fluoroborylene iron and ruthenium carbonyls M(BF)(CO) m (m =4, 3) and M2(BF)2(CO) n (n =7, 6) (M=Fe, Ru) are predicted to be very similar. For Ru(BF)(CO)4 the trigonal bipyramidal structures with the BF group in an equatorial position and in an axial position are both found with the equatorially substituted isomer lying ∼2kcal/mol below the axially substituted isomer. For the coordinately unsaturated Ru(BF)(CO)3 both singlet and triplet structures are found derived from the equatorially substituted Ru(BF)(CO)4 structure by removal of an equatorial CO group. The structures for the binuclear derivatives Ru2(BF)2(CO) n (n =7, 6) provide examples of lower energy structures with bridging BF groups relative to similar structures with bridging CO groups. The lowest energy Ru2(BF)2(CO)7 structure has two bridging BF groups and one CO group and is qualitatively similar to the well-known Fe2(CO)9 structure with three bridging CO groups. All of the structures of the unsaturated Ru2(BF)2(CO)6 within 30kcal/mol of the global minimum have two bridging groups. The structure with one bridging CO group and one bridging BF group lies ∼16kcal/mol above the global minimum with two bridging BF groups again showing the preference for bridging BF groups over bridging CO groups. A triplet Ru2(BF)2(CO)6 structure with two bridging BF groups was also found but at the high energy of ∼26kcal/mol above that of the corresponding singlet global minimum. This singlet–triplet splitting is much larger than the singlet–triplet splitting of the corresponding Fe2(BF)2(CO)6. [Copyright &y& Elsevier]

Abstract: Theoretical studies on (C8H8)2Nb2(CO) n (n = 6, 5, 4, 3, 2, 1) predict structures mainly with octahapto and tetrahapto C8H8 rings. In all cases, the lowest energy singlet spin state structures lie below the corresponding lowest energy triplet spin state structures. Thus the lowest energy (C8H8)2Nb2(CO)4 structure has two η8-C8H8 rings and an unbridged Nb–Nb single bond of length ∼3.15 Å. The lowest energy (C8H8)2Nb2(CO)2 structure has two η8-C8H8 rings but a doubly bridged Nb bond of length ∼2.64 Å. The lowest energy structure of (C8H8)2Nb2(CO)3 also has a formal Nb bond of similar length (2.66 Å) but with only one of the rings fully coordinated as an octahapto η8-C8H8 ligand. The other C8H8 ring in this tricarbonyl has “slipped” to form a hexahapto η6-C8H8 ligand. The lowest energy structure of the monocarbonyl (C8H8)2Nb2(CO) again has two octahapto η8-C8H8 rings and an extremely short Nbce of 2.45 Å, suggesting a formal quadruple bond. The lowest energy structures for the carbonyl-richer species (C8H8)2Nb2(CO) n (n = 6, 5) have one η8-C8H8 and one η4-C8H8 ring (n = 5) and two η4-C8H8 rings (n = 6). The qualitatively assigned Nb–Nb bond orders are consistent with the Wiberg bond indices obtained from the Weinhold natural bond orbital analysis. Comparison of the (C8H8)2Nb2(CO) n (n = 6, 5, 4, 3, 2, 1) derivatives with the isovalent (C7H7)2Mo2(CO) n is made. [Copyright &y& Elsevier]

Graphical abstract The lowest energy structures for the tetracarbonyl (C 4 H 4 BH) 2 Co 2 (CO) 4 are doubly bridged structures similar to (C 4 H 4 BCH 3) 2 Co 2 (CO) 4. The lowest energy structures for the unsaturated derivatives (C 4 H 4 BH) 2 Co 2 (CO) n (n = 3, 2, 1) have bridging borole ligands with agostic hydrogen atoms from their B–H groups to a cobalt atom. Highlights • The (C 4 H 4 BH) 2 Co 2 (CO) n (n = 4, 3, 2, 1) systems have been examined by density functional theory. • Low-energy doubly bridged (C 4 H 4 BH) 2 Co 2 (CO) 2 (µ-CO) 2 structures are found similar to (C 4 H 4 BCH 3)Co 2 (CO) 2 (µ-CO) 2. • The lowest energy structures for (C 4 H 4 BH) 2 Co 2 (CO) n (n = 3, 2, 1) have agostic B–H hydrogens from bridging borole ligands. Abstract The (C 4 H 4 BH) 2 Co 2 (CO) n (n = 4, 3, 2, 1) systems have been examined by density functional theory for comparison with the analogous (C 4 H 4 BCH 3) 2 Co 2 (CO) n systems. For the tetracarbonyl (C 4 H 4 BH) 2 Co 2 (CO) 4 a higher energy unbridged structure is found at ∼7 kcal/mol above the lowest energy doubly bridged structure similar to (C 4 H 4 BCH 3) 2 Co 2 (CO) 4. The lowest energy structures for the unsaturated derivatives (C 4 H 4 BH) 2 Co 2 (CO) n (n = 3, 2, 1) have bridging borole ligands with agostic hydrogen atoms from their B–H groups to a cobalt atom. Structures without agostic hydrogens analogous to the low-energy structures for the corresponding methylborole derivatives (C 4 H 4 BCH 3) 2 Co 2 (CO) n are higher energy (C 4 H 4 BH) 2 Co 2 (CO) n structures. [ABSTRACT FROM AUTHOR]

The geometries and energetics of the binuclear unsubstituted borole iron carbonyls (C 4 H 4 BH) 2 Fe 2 (CO) n ( n = 5, 4, 3, 2, 1) have been studied by density functional theory for comparison with the previously studied related substituted borole iron carbonyls (C 4 H 4 BR) 2 Fe 2 (CO) n [R = CH 3 , (CH 3 ) 2 N] having different substituents on the boron atoms. The lowest energy (C 4 H 4 BH) 2 Fe 2 (CO) n ( n = 5, 4, 3) structures have terminal borole ligands related to those in the (C 4 H 4 BR) 2 Fe 2 (CO) n [R = CH 3 , (CH 3 ) 2 N] systems as well the isoelectronic (η 5 -C 5 H 5 ) 2 Mn 2 (CO) n systems. However, the lowest energy structure of the dicarbonyl (C 4 H 4 BH) 2 Fe 2 (CO) 2 is an unusual quintet spin state structure with one of the borole ligands bridging the central Fe 2 unit by forming a three-center two-electron B H Fe bond to one iron atom as well as functioning as a pentahapto ligand to the other iron atom. For the (C 4 H 4 BR) 2 Fe 2 (CO) n [R = CH 3 , (CH 3 ) 2 N] systems the tricarbonyls ( n = 3) having formal Fe Fe triple bonds of lengths ∼2.2 Å analogous to the experimentally known (η 5 -Me 5 C 5 ) 2 Mn 2 (μ-CO) 3 structure appear to be favorable structures. An analogous (C 4 H 4 BH) 2 Fe 2 (μ-CO) 3 structure is found for the unsubstituted borole ligand. However, this structure appears to be disfavored relative to disproportionation into (C 4 H 4 BH) 2 Fe 2 (CO) n+ 1 + (C 4 H 4 BH) 2 Fe 2 (CO) n −1 . [ABSTRACT FROM AUTHOR]

The binuclear 1,3-diphosphacyclobutadiene manganese carbonyls (Me 2 C 2 P 2 ) 2 Mn 2 (CO) n ( n = 6, 5, 4, 3) have been investigated by density functional theory. The lowest energy (Me 2 C 2 P 2 ) 2 Mn 2 (CO) n ( n = 6, 5) structures are found to have two mononuclear (Me 2 C 2 P 2 ) 2 Mn 2 (CO) m fragments linked by P→M dative bonds. The lowest energy isomers with terminal η 4 -Me 2 C 2 P 2 rings and Mn–Mn bonds lie ∼15 and ∼22 kcal/mol above these global minima for (Me 2 C 2 P 2 ) 2 Mn 2 (CO) 6 and (Me 2 C 2 P 2 )Mn 2 (CO) 5 , respectively. For the (Me 2 C 2 P 2 ) 2 Mn 2 (CO) 4 system, singlet structures with terminal η 4 -Me 2 C 2 P 2 rings and formal Mn Mn triple bonds are of comparable energies to triplet structures consisting of (Me 2 C 2 P 2 ) 2 Mn 2 (CO) m fragments linked by two P→M dative bonds. All of the low-energy (Me 2 C 2 P 2 ) 2 Mn 2 (CO) 3 structures have terminal η 4 -Me 2 C 2 P 2 rings and three bridging CO groups with short Mn–Mn distances suggesting formal multiple bonds. [ABSTRACT FROM AUTHOR]

A theoretical study of the cyclodimerization of (Cy3P)2Pt(BO)Br (1Br) and [(Cy3P)2Pt(BO)]+ (1) (Cy = cyclohexyl) suggests that the reactivity of the BO ligand is primarily controlled by M←BO σ donation. Therefore, increasing the electron density at the metal center through strong σ-donor and weak π-acceptor ancillary ligands and a low formal metal oxidation state are suggested to reduce the polarity of the boronyl ligand and thus lower its reactivity toward cyclodimerization. The stable 1Br has lower Pt←BO σ donation and thus a less electrophilic boron atom, leading to a less polarized BO ligand. However, 1 is unstable in dichloromethane, since the dicationic dimer and transition state are highly stabilized by strong electrostatic interactions. [ABSTRACT FROM AUTHOR]

Aceheptylene as its dimethyl derivative is the most readily available tricyclic non-benzenoid aromatic hydrocarbon. This dimethyl derivative has been used to synthesize the trinuclear iron carbonyl complex (C 14 H 8 Me 2 )Fe 3 (CO) 8 . Theoretical studies on the unsubstituted complex C 14 H 10 Fe 3 (CO) 8 show the experimental structure to be the lowest energy structure. Related structures having the aceheptylene ligand partitioned into an azulene subunit bonded to an Fe 2 (CO) 5 moiety and a cis 1,3-diene subunit bonded to an Fe(CO) 3 moiety are the lowest energy C 14 H 10 Fe 3 (CO) 8 structures. Higher energy C 14 H 10 Fe 3 (CO) 8 structures with the aceheptylene ligand partitioned into two equivalent outer cis 1,3-diene subunits bonded to Fe(CO) 3 moieties and a central fulvene subunit bonded to an Fe(CO) 2 moiety are also found. Low energy structures of the C 14 H 10 Fe 3 (CO) 9 precursor to C 14 H 10 Fe 3 (CO) 8 are found with three separate Fe(CO) 3 moieties bonded to separate cis 1,3-diene subunits of the aceheptylene ligand leaving an uncomplexed C C double bond. Deleting the five-membered ring from aceheptylene gives heptalene, which is predicted to form viable C 12 H 10 Fe 3 (CO) n ( n = 9, 8) complexes. The lowest energy C 12 H 10 Fe 3 (CO) 9 structure has one Fe(CO) 3 moiety bonded to a cis 1,3-diene subunit of one seven-membered ring and two Fe(CO) 3 moieties bonded to overlapping cis 1,3-diene subunits on opposite sides of the other seven-membered ring sharing two carbon atoms thus leaving an uncomplexed C C bond. The lowest energy C 12 H 10 Fe 3 (CO) 8 structure is derived from such a C 12 H 10 Fe 3 (CO) 9 structure by CO loss accompanied by complexation of the uncomplexed C C double bond. [ABSTRACT FROM AUTHOR]

Cobalt carbonyls such as Co 2 (CO) 8 are among the most frequently used catalyst precursors for the cyclotrimerization of alkynes to form benzene derivatives. In order to gain some insight regarding possible intermediates in such reactions, the species (C 6 R 6 )Co 2 (CO) n ( n = 6, 5, 4, 3; R = H, F, CF 3 ) have been investigated by density functional theory. The thermochemistry of these systems is found to be very dependent on the substituent R. The lowest energy (C 6 H 6 )Co 2 (CO) n structures ( n = 6, 5, 4, 3) by at least 8 kcal/mol all have cis geometries with intact benzene rings and Co–Co bonds. The benzene rings are bent for the more highly unsaturated (C 6 H 6 )Co 2 (CO) n ( n = 4, 3) structures. The tetracarbonyl (C 6 H 6 )Co 2 (CO) 4 is disfavored with respect to disproportionation into (C 6 H 6 )Co 2 (CO) 5 and (C 6 H 6 )Co 2 (CO) 3 . In addition, (C 6 H 6 )Co 2 (CO) 6 is marginally viable with respect to benzene dissociation to give Co 2 (CO) 6 , which has long been recognized as an intermediate in the conversion of Co 2 (CO) 8 to Co 4 (CO) 12 . The perfluoro and trifluoromethyl systems (C 6 R 6 )Co 2 (CO) n (R = F, CF 3 ; n = 6, 5, 4, 3) differ from (C 6 H 6 )Co 2 (CO) n in having “flyover” derivatives rather than cyclized benzene derivatives as the lowest energy structures for the tetracarbonyls (C 6 R 6 )Co 2 (CO) 4 . This may relate to difficulties in the cyclization of the C 6 chain with the more hindered F and CF 3 substituents relative to hydrogen on the end carbon atoms. These “flyover” tetracarbonyl appear to be thermodynamic “sinks” consistent with the experimental isolation of [C 6 (CF 3 ) 6 ]Co 2 (CO) 4 as a stable product from Co 2 (CO) 8 /CF 3 C CCF 3 reactions. [ABSTRACT FROM AUTHOR]

The recently synthesized 1,2-diaza-3,5-diborolyl ligand is a BN analog of the cyclopentadienyl ligand that has been recently used for the synthesis of a BN analog of ferrocene. The binuclear 1,2-diaza-3,5-diborolyl iron carbonyl derivatives (Me 4 B 2 N 2 CH) 2 Fe 2 (CO) n ( n = 5, 4, 3, 2) have now been investigated by density functional theory for comparison with the corresponding cyclopentadienyliron carbonyl systems, (C 5 H 5 ) 2 Fe 2 (CO) n . The lowest energy (Me 4 B 2 N 2 CH) 2 Fe 2 (CO) n ( n = 4, 3, 2) structures have two bridging CO groups. For (Me 4 B 2 N 2 CH) 2 Fe 2 (CO) 3 a triplet triply bridged (Me 4 B 2 N 2 CH) 2 Fe 2 (μ-CO) 3 structure is analogous to the experimentally known stable compounds (η 5 -C 5 R 5 ) 2 Fe 2 (μ-CO) 3 (R = H, CH 3 ). From the thermochemistry results, the doubly bridged singlet (Me 4 B 2 N 2 CH) 2 Fe 2 (CO) 2 (μ-CO) 2 structure appears to a promising synthetic objective. The energies of the triplet (Me 4 B 2 N 2 CH) 2 Fe 2 (CO) 3 and (Me 4 B 2 N 2 CH) 2 Fe 2 (CO) 2 structures are lower than those of the corresponding singlet structures. The Wiberg bond indices of the iron–iron bonds determined by the NBO method correlate well with the formal bond orders suggested by the Fe Fe distances and electron counting. The (Me 4 B 2 N 2 CH) 2 Fe 2 (CO) 5 structures lack an iron–iron bond and require only ∼2 kcal/mol in energy for decarbonylation to (Me 4 B 2 N 2 CH) 2 Fe 2 (CO) 4 . In all of the (Me 4 B 2 N 2 CH) 2 Fe 2 (CO) n ( n = 4, 3, 2) structures, the predicted Fe N and Fe B distances are close to those in the ferrocene analog [η 5 -(CH 2 ) 3 N 2 (BPh) 2 CMe] 2 Fe. [ABSTRACT FROM AUTHOR]

The sulfur analogue of the well-known Ni(CO)4, namely, Ni(CS)4, has been observed spectroscopically in low temperature matrices but is not known as a stable species under ambient conditions. Theoretical studies show that Ni(CS)4 with monomeric CS ligands and tetrahedrally coordinated nickel is disfavored by ~17 kcal/mol relative to unusual isomeric Ni(C2S2)2 structures. In the latter structures the CS ligands couple pairwise through C-C bond formation to give dimeric S-C-C-S ligands, which bond preferentially to the nickel atom through their C-S bonds rather than their C-C bonds. Coupling of CS ligands in the lowest energy binuclear Ni2(CS)n (n = 7, 6, 5) structures results in cyclization to give remarkable CnSn (n = 5, 6) ligands containing five- and six-membered carbocyclic rings. Such ligands, which are the sulfur analogues of the well-known croconate (n = 5) and rhodizonate (n = 6) oxocarbon ligands, function as bidentate ligands to the central Ni2 unit. Higher energy Ni2(CS)n (n = 7, 6, 5) structures contain dimeric C2S2 ligands, which can bridge the central Ni2 unit. Dimeric C2S2 ligands rather than tetrathiosquare C4S4 ligands are found in the lowest energy Ni2(CS)4 structures. [ABSTRACT FROM AUTHOR]

The trifluoromethyl isocyanide ligand, CF 3 NC is of interest in being a strong back-bonding ligand similar to carbon monoxide. Furthermore, Lentz and coworkers have shown that free CF 3 NC is stable enough in the free state at low temperatures to use as a reagent for the synthesis of metal complexes. In this connection the binuclear (CF 3 NC) 2 Fe 2 (CO) n ( n = 7, 6, 5) and mononuclear (CF 3 NC)Fe(CO) n ( n = 4, 3) have been studied by density functional theory. Coupling of CF 3 NC ligands to form a bridging η 2 ,η 2 -μ-CF 3 NCCNCF 3 ligand is predicted to occur in the lowest energy binuclear (CF 3 NC) 2 Fe 2 (CO) n ( n = 6, 5) structures. A similarly coupled Fe 2 (CO) 7 (η 2 ,η 2 -μ-CF 3 NCCNCF 3 ) structure is also found for (CF 3 NC) 2 Fe 2 (CO) 7 . However, this structure lies ∼11 kcal/mol in energy above the lowest energy Fe 2 (CO) 6 (μ-CO)(μ-CF 3 CN) 2 isomer having separate bridging CF 3 NC ligands analogous to the well-known triply bridged Fe 2 (CO) 9 structure. The mononuclear derivative (CF 3 NC)Fe(CO) 4 is shown to be similar to Fe(CO) 4 (CS) in having equatorial and axially substituted trigonal bipyramidal isomers of nearly identical energies within 1 kcal/mol. The binuclear (CF 3 NC) 2 Fe 2 (CO) n ( n = 7, 6) derivatives are predicted to be viable toward dissociation into the mononuclear fragments (CF 3 NC)Fe(CO) m ( m = 4 and/or 3) by substantial energies exceeding 29 kcal/mol. [ABSTRACT FROM AUTHOR]

Highlights: [•] The C7H7 ring can be either a heptahapto or pentahapto ligand in low-energy (C7H7)2V2(CO) n (n =5, 4, 3) structures. [•] (C7H7)2V2(CO) n (n =5, 4, 3) structures with V V triple bonds and 18-electron vanadium configurations are preferred. [•] A low-energy linear triplet (C7H7)2V2 structure has rare D 7h symmetry and a V V triple bond. [•] The lowest energy singlet (C7H7)2V2 structure has an ultrashort V–V distance of 1.84Å and a formal sextuple bond. [ABSTRACT FROM AUTHOR]

Abstract: The bis(methylborabenzene)metal sandwich compounds (η6-C5H5BCH3)2M of the first row transition metals from Ti to Ni have been examined by density functional theory. The four of these seven methylborabenzene sandwich compounds that have been synthesized, namely the V, Cr, Fe, and Co derivatives, are predicted to have quartet, triplet, singlet, and doublet spin states, respectively, in accord with experiment. For (η6-C5H5BCH3)2Ti the singlet spin state structure lies only ∼2 kcal/mol below the triplet spin state structure. This energetic relationship is reversed for (η6-C5H5BCH3)2Ni for which the triplet spin state structure lies ∼2 kcal/mol in energy below the singlet spin state structure. Similarly the sextet (η6-C5H5BCH3)2Mn spin state structure lies only ∼2 kcal/mol below the corresponding doublet spin state structures. These observations suggest possible spin-crossover behavior for these three still unknown (η6-C5H5BCH3)2M (M = Ti, Mn, Ni) systems. The M–C and M–B distances from the metal to the methylborabenzene ligand increase for a given (η6-C5H5BCH3)2M system as the spin multiplicity is increased. This suggests a weakening of the metal–ligand bond with an increase in the spin multiplicity. The energy surfaces of all of these (η6-C5H5BCH3)2M sandwich compounds are complicated by multiple local minima differing only by the rotation of one methylborabenzene ring relative to the other such ring. The energy differences between these rotamers for the same spin state are generally less than the energy differences between different spin states for a given (η6-C5H5BCH3)2M sandwich compound. [Copyright &y& Elsevier]

The tetramethyleneethane (TME) ligandis found in the η3,η3complex trans-(η3,η3-TME)Ni2Cp2and the η4,η4complex trans-(η4,η4-TME)Co2Cp2, which have both been synthesizedand structurally characterized by X-ray crystallography. The structuresof the complete series of (TME)M2Cp2derivativesof the first-row transition metals from Ti to Ni have now been investigatedby density functional theory. The experimentally known nickel andcobalt complexes are found to have closed-shell electronic groundstates. The lowest energy structure for the iron complex is the tripletspin state trans-(η4,η4-TME)Fe2Cp2structure with geometrysimilar to that of the lowest energy cobalt structure. All of thelow-energy (TME)M2Cp2structures for manganeseand the first-row transition metals to the left of manganese (Cr,V, and Ti) exhibit cis-(η4,η4-TME)M2Cp2stereochemistry, therebyproviding the possibility for direct metal–metal interactions.Vanadium is the only first-row transition metal to the left of cobaltwhere the lowest energy (TME)M2Cp2structureis a singlet spin state, suggesting limited applicability of the 18-electronrule in these systems. The frontier molecular orbitals of these cis-(η4,η4-TME)M2Cp2systems have been examined in order to provide insightregarding metal–metal bonding. Thus, low-energy cis-(η4,η4-TME)Mn2Cp2structures are found in both quintet and triplet spin stateswith formal MnMn double bonds. The lowest energy cis-(η4,η4-TME)Cr2Cp2and cis-(η4,η4-TME)Ti2Cp2structures have tripletspin states with a formal CrCr triple bond and a formal TiTidouble bond, respectively. The lowest energy cis-(η4,η4-TME)V2Cp2structureis a singlet structure with a formal VV triple bond. [ABSTRACT FROM AUTHOR]

Highlights: [•] The structures of (C5F6)Co2(CO) n (n =8, 7, 6, 5, 4) have been investigated using density functional theory. [•] Trihapto/monohapto bonding of the C5F6 ring to the Co2 unit is preferred in (C5F6)Co2(CO) n (n =7, 6, 5, 4). [•] Viable bis(monohapto) structures are found for C5F6Co2(CO)8. [•] Cobalt–cobalt bonds are found in the lowest energy (C5F6)Co2(CO) n (n =6, 5, 4) structures. [ABSTRACT FROM AUTHOR]

Highlights: [•] A cis-(η5,η5-C8H6)Co2(CO)4 structure related to the experimental structure is predicted. [•] The Co–Co interaction in cis-(η5,η5-C8H6)Co2(CO)4 has a Wiberg bond index of only 0.06. [•] The low-energy (C8H6)Co2(CO) n (n =3, 2) structures also have pentahapto pentalene ligands. [•] The carbonyl-rich (C8H6)Co2(CO) n (n =6, 5) structures illustrate considerable diversity of pentalene bonding modes. [Copyright &y& Elsevier]

Abstract: The trimethylenemethane ligand is found in the experimentally known and structurally characterized mononuclear iron carbonyl derivative (CH2)3CFe(CO)3, which may be regarded as a substitution product of Fe(CO)5. The structures of trinuclear trimethylenemethane iron carbonyl derivatives similarly related to the well-known doubly bridged Fe3(CO)12 structure have now been investigated by density functional theory. The lowest energy [(CH2)3C]Fe3(CO)10 structures likewise have two CO bridges and can be derived from the known Fe3(CO)12 structure by replacement of two terminal CO groups with either an unsymmetrical edge-bridging or face-bridging trimethylene methane ligand while preserving the central Fe3 triangle. However, replacing four CO groups in Fe3(CO)12 with two trimethylenemethane ligands to give [(CH2)3C]2Fe3(CO)8 is predicted unexpectedly to give a very different type of structure. In this structure one edge of the Fe3 triangle in Fe3(CO)12 is broken to form a bent Fe–Fe–Fe chain with the trimethylenemethane ligands bonded to the end iron atoms of this triiron chain. This [(CH2)3C]2Fe3(CO)8 structure appears to be very favorable, since it lies ∼22kcal/mol below alternative structures. We anticipate that both [(CH2)3C]Fe3(CO)10 and [(CH2)3C]2Fe3(CO)8 should be sufficiently stable to be synthesized from the known (CH2)3CFe(CO)3 by thermolysis or photolysis with suitable iron carbonyls. [Copyright &y& Elsevier]

Abstract: The structures and thermochemistry of the binuclear cyclopentadienylcobalt carbonyl boronyls Cp2Co2(BO)2(CO) n (Cp = η5-C5H5; n = 2, 1, 0) were investigated by density functional theory. Low energy structures were found of the following types: (1) Structures in which the BO groups are all one-electron donors analogous to the isoelectronic Cp2Fe2(CO) n+2 structures; (2) Structures in which the two BO groups have coupled to form bridging B2O2 ligands, which may be either four- or six-electron donors; (3) Structures with three-electron donor bridging BO groups, bonded to one metal through the boron atom and to the other metal through the oxygen atom. The lowest energy Cp2Co2(BO)2(CO)2 structures are singlet trans and cis isomers of doubly bridged structures analogous to the well-known isoelectronic Cp2Fe2(CO)2(μ-CO)2. The lowest energy Cp2Co2(BO)2(CO) structure is a triplet triply bridged structure analogous to the isoelectronic stable triplet state molecule Cp2Fe2(μ-CO)3. Higher energy Cp2Co2(BO)2(CO) structures have trans or cis bridging B2O2 ligands. The lowest energy Cp2Co2(BO)2 structure is a triplet state structure with a six-electron donor bridging trans-η4-μ-B2O2 ligand. The lowest energy singlet Cp2Co2(BO)2 structure has two one-electron donor bridging μ-BO groups and a formal Co Co triple bond similar to the predicted lowest energy Cp2Fe2(CO)2 structure. [Copyright &y& Elsevier]

Abstract: The experimentally known methylborabenzene iron carbonyl (C5H5BCH3)2Fe2(CO)4 and its decarbonylation products (C5H5BCH3)2Fe2(CO) n (n = 3, 2) have been studied by density functional theory for comparison with their cyclopentadienyl analogs. The lowest energy (η6-C5H5BCH3)2Fe2(CO)4 structures are the experimentally known singlet doubly bridged cis-(η6-C5H5BCH3)2Fe2(CO)2(μ-CO)2 and the corresponding trans isomer similar to the corresponding (η5-C5H5)2Fe2(CO)2(μ-CO)2 system. Also the triplet triply bridged (η6-C5H5BCH3)2Fe2(μ-CO)3 is the lowest energy tricarbonyl structure similar to the cyclopentadienyl system. However, significant differences between the methylborabenzene and cyclopentadienyl derivatives are found in the dicarbonyl systems. A singlet (η5-C5H5)2Fe2(μ-CO)2 structure with a short Fe Fe distance of ∼2.1 Å was previously found to be the lowest energy structure in the cyclopentadienyl system. An analogous methylborabenzene structure (η6-C5H5BCH3)2Fe2(μ-CO)2 is found as the lowest energy singlet structure. However, an unsymmetrical quintet (η6-C5H5BCH3)Fe Fe(CO)2(η6-C5H5BCH3) structure is predicted to lie ∼22 kcal/mol below this singlet structure. The existence of this low-energy, high-spin (η6-C5H5BCH3)2Fe2(CO)2 structure makes (η6-C5H5BCH3)2Fe2(μ-CO)3 disfavored with respect to disproportionation into (η6-C5H5BCH3)2Fe2(μ-CO)4 + (η6-C5H5BCH3)2Fe2(μ-CO)2 unlike its cyclopentadienyl analog. [Copyright &y& Elsevier]

Highlights: [•] The potential energy surface of Cp2Pd2(BO)2 has 11 low energy structures. [•] These Cp2Pd2(BO)2 structures includes both perpendicular and coaxial structures. [•] Several Cp2Pd2(BO)2 structures have the BO group directly bonded to a Cp carbon atom. [•] A highly favored coaxial Cp2Pd2(μ-BF)2 structure is found. [Copyright &y& Elsevier]

Highlights: [•] The lowest energy Fe2(CF2)(CO) n (n =7, 6, 5) structures have a bridging rather than terminal CF2 group. [•] Iron–iron triple and quadruple bonds are avoided in the highly unsaturated Fe2(CF2)(CO) n (n =6, 5) structures. [•] The lowest energy singlet Fe2(CF2)(CO)5 structure has an unprecedented kind of four-electron donor η2-μ-CF2 group. [Copyright &y& Elsevier]