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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 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]

The two tetranuclear iron carbonyl systems EFe4(CO)n (E = Sn, C) containing central group 14 interstitial atoms differ in that spiropentane-like SnFe4(CO)16 has been synthesized in the tin system whereas the butterfly CFe4(CO)13, with three fewer carbonyl groups is the carbonyl-richest tetranuclear iron carbonyl carbide that has been synthesized. In order to clarify this point, the complete SnFe4(CO)n (n = 16, 15, 14, 13, 12) series has been studied by density functional theory for comparison with earlier similar studies on their CFe4(CO)n analogues. The experimentally observed spiropentane-like Sn[Fe2(CO)8]2 structure is found to be the lowest energy structure for the SnFe4(CO)16 system as it is for the experimentally unknown CFe4(CO)16 system. Loss of a CO group from Sn[Fe2(CO)8]2 joins the two Fe2(CO)8 units by a third Fe–Fe bond to give an SnFe4(CO)15 structure with a bonded four-atom Fe–Fe–Fe–Fe chain. Further CO loss from SnFe4(CO)15 adds a fourth Fe–Fe bond in the lowest energy SnFe4(CO)14 structure. The lowest energy SnFe4(CO)13 structure is analogous to that of the experimentally known iron carbonyl carbide CFe4(CO)13 with a central Fe4 butterfly having five Fe–Fe bonds. The energetics of CO dissociation from the EFe4(CO)n (E = C, Sn; n = 16, 15, 14, 13) species account for the experimentally observed differences between the systems with central tin and central carbon atoms. Thus for the tin systems the CO dissociation energy from SnFe4(CO)16 is relatively high at ∼50 kcal mol−1 consistent with its experimental observation as a stable species. However, for the tetranuclear iron carbonyl carbides CFe4(CO)n, the CO dissociation energies of the species with more than 13 CO groups are all very small or even negative suggesting CFe4(CO)13 to be the carbonyl-richest viable iron tetracarbonyl carbide consistent with experiment. [ABSTRACT FROM AUTHOR]

The opposed and parallel structures for the binuclear bis(azulene) 'submarine' sandwiches (C10H8)2M2 (M = Ti, V, Cr, Mn, Fe, Co, Ni) have been optimized using density functional theory. The lowest energy (C10H8)2M2 structures of the early transition metals Ti, V, Cr, and Mn have the azulene units functioning as bis(pentahapto) ligands to each metal atom similar to the azulene ligand in the long-known molybdenum carbonyl complex (η5,η5-C10H8)Mo2(CO)6. The metal-metal bonds in these early transition metal structures have distances and Wiberg bond indices consistent with the formal bond orders required to give each metal atom an 18-electron configuration for the singlet structures and a 17-electron configuration for the triplet structures. For the later transition metals Fe, Co, and Ni, the lowest energy (C10H8)2M2 structures contain pentahapto-trihapto azulene ligands with an uncomplexed CC double bond, similar to that in the long-known iron carbonyl complex (η5,η3-C10H8)Fe2(CO)5. The parallel (η5,η3-C10H8)2M2 (M = Fe, Co, Ni) structures contain metallocene subunits with their metal atoms at long nonbonding distances of 3.5-3.9 Å from the other metal atom, which is located between the azulene C7 rings. Higher energy opposed (C10H8)2Fe2 structures contain an unprecedented distorted η6,η4-azulene ligand using six carbon atoms for bonding to one iron atom as a hexahapto fulvene ligand and the remaining four carbon atoms for bonding to the other iron atom as a tetrahapto diene ligand. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Oxidative degradation of the octahedral dianion [Fe6C(CO)16]2− with an interstitial carbon atom leads eventually to the neutral Fe4C(CO)13 cluster with a butterfly-shaped central Fe4C unit. The complete series of related Fe4C(CO)n (n = 16, 15, 14, 13, 12, 11) derivatives have now been investigated using density functional theory. For the lowest energy Fe4C(CO)n (n = 16, 15, 14, 13) structures the geometries obey the n + f = 18 rule where f is the number of Fe–Fe bonds. This leads to a spiropentane geometry with two Fe–Fe bonds for Fe4C(CO)16, a central bent Fe–Fe–Fe–Fe chain for Fe4C(CO)15, a distorted trigonal pyramidal structure with four Fe–Fe bonds for Fe4C(CO)14, and the experimentally observed butterfly structure with five Fe–Fe bonds for Fe4C(CO)13. A symmetrical higher energy centered tetrahedral structure for Fe4C(CO)12 with six Fe–Fe bonds also follows the n + f = 18 rule. However, the lowest energy Fe4C(CO)n (n = 12, 11) structures are derived from the lowest energy Fe4C(CO)13 structure by removal of CO groups with retention of the central Fe4C butterfly unit. [ABSTRACT FROM AUTHOR]

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The metal carbonyl complexes [η4-(CH2)3C]Fe(CO)3 and [η4-(CH2)3C]Cr(CO)4 have been synthesized containing the umbrella-shaped trimethylenemethane ligand. The prospect of using this ligand in the metal sandwich complexes [(CH2)3C]2M (M = Ti, V, Cr, Mn, Fe, Co, Ni) has now been investigated by density functional theory. The lowest energy structures of such complexes have the metal atom sandwiched between two tetrahapto trimethylenemethane ligands. Singlet spin state structures are strongly preferred for the titanium and nickel derivatives and doublet spin state structures for the vanadium and cobalt derivatives. Similarly, the triplet spin state is preferred for the iron derivative by more than 11 kcal mol−1. The preferred spin states for the chromium and manganese derivatives depend on the functional used for the structure optimization. Thus the B3LYP and B3LYP* methods predict the higher spin states, namely triplet for chromium and quartet for manganese. However, the BP86 method predicts the lower spin states of singlet for chromium and doublet for manganese. The higher spin state structures for the late transition metal derivatives, namely quintet [(CH2)3C]2Fe, quartet [(CH2)3C]2Co, and triplet [(CH2)3C]2Ni, have trihapto rather than tetrahapto trimethylenemethane ligands. The frontier molecular orbitals in the singlet [(CH2)3C]2M derivatives (M = Ti, Ni) suggest strong metal–ligand σ and π bonding but insignificant metal–ligand δ bonding. [ABSTRACT FROM AUTHOR]

Abstract: Dicobalt octacarbonyl is known to react with diolefins to give substitution products of the types (diene)Co2(CO)6 and (diene)2Co2(CO)4. The butadiene derivatives (C4H6)Co2(CO) n (n =6, 5, 4, 3, 2) have been investigated by density functional theory using the B3LYP and BP86 methods. The lowest energy (C4H6)Co2(CO) n (n =6, 5, 4) structures have bridging CO groups and terminal butadiene ligands. For the (C4H6)Co2(CO)6 and (C4H6)Co2(CO)5 structures the Coces of ∼2.5Å suggest formal single bonds. However, for the lowest energy (C4H6)Co2(CO)4 structure the significantly shorter Coce of ∼2.3Å suggests the formal triple bond required to give the cobalt atom the favored 18-electron configuration. Bridging butadiene ligands are also found in (C4H6)Co2(CO) n structures including all of the lowest energy (C4H6)Co2(CO)3 and (C4H6)Co2(CO)2 structures. Both the B3LYP and BP86 methods predict butadiene dissociation from (C4H6)2Co2(CO)4 to be energetically favored over CO dissociation by ∼8kcal/mol. For (C4H6)2Co2(CO) n (n =3, 2) the BP86 method predicts CO dissociation to be favored energetically over butadiene dissociation by ∼8kcal/mol. However, the B3LYP method predicts essentially equal CO and butadiene dissociation energies within ∼1kcal/mol from (C4H6)2Co2(CO) n (n =3, 2). [Copyright &y& Elsevier]

The highly unsaturated binuclear butadiene iron carbonyls (C4H6)2Fe2(CO)n (n = 2, 1) have been examined using density functional theory. For (C4H6)2Fe2(CO)n (n = 2, 1), both coaxial and perpendicular structures are found. The global minima of (C4H6)2Fe2(CO)n (n = 2, 1) are the perpendicular structures 2Q-1 and 1Q-1, respectively, with 17- and 15-electron configurations for the iron atoms leading to quintet spin states. The Fe=Fe distance of 2.361 Å (M06-L) in the (C4H6)2Fe2(CO)2 structure 2Q-1 suggests a formal double bond. The Fe=Fe bond distance in the (C4H6)2Fe2(CO) structure 1Q-1 is even shorter at 2.273 Å (M06-L), suggesting a triple bond. Higher energy (C4H6)2Fe2(CO)n (n = 2, 1) structures include structures in which a bridging butadiene ligand is bonded to one of the iron atoms as a tetrahapto ligand and to the other iron atom through two agostic hydrogen atoms from the end CH2 groups. Singlet (C4H6)2Fe2(CO) structures with formal Fe-Fe quadruple bonds of lengths ∼2.05 Å were also found but at very high energies (∼47 kcal/mol) relative to the global minimum. [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]

Abstract: Density functional calculations on the Fe2(CO)6(μ-SR)2, Co2(η5-C5H5)2(μ-SR)2, and Fe2(η6-C6H6)2(μ-SR)2 systems (R=CH3, CF3) predict butterfly structures with a non-planar central M2S2 unit containing one M–M bond for the “body” of the butterfly and four M–S bonds at the edges of the “wings” of the butterfly. These butterfly structures are found to be of three types. In every case the lowest energy structures are those with the two RS groups oriented in opposite directions (the ud isomers). The other two possible stereoisomers, namely the uu and dd isomers with equivalent RS groups, are found at significantly higher relative energies. Structures with planar Fe2S2 units with 180° S–Fe–Fe–S dihedral angles are found for the Fe2(CO)6(μ-SR)2 derivatives but always at significantly higher energies than the butterfly structures, ranging from 21 to 29kcal/mol above the global minima. The nature of the RS substituents has no significant effect on the relative stability of the isomers. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) studies on Mn2(CS)2(CO)8using the B3LYP and BP86 methods show that no less than eight different unbridged structures are of significantly lower energies than the lowest energy doubly bridged structure. The Mn–Mn single bonds in these Mn2(CS)2(CO)8structures range from 2.99 ± 0.02 for the four structures with staggered equatorial CO/CS groups to 3.12 ± 0.04 for the four structures with eclipsed equatorial CO/CS groups. The six lowest energy Mn2(CS)2(CO)7structures all have four-electron donor bridging η2-μ-CE groups (E = S, O) and formal Mn–Mn single bonds of lengths 2.95 ± 0.01 , rather than only two-electron donor CO and CS groups and formal MnMn double bonds. The Mn2(CS)2(CO)7structures with an η2-μ-CS group are of lower energy than those with an η2-μ-CO group. These Mn2(CS)2(CO)7structures are similar to the lowest energy structure for Mn2(CO)9predicted previously as well as (Ph2PCH2PPh2)2Mn2(CO)4(η2-μ-CO), which has been synthesized and structurally characterized by X-ray diffraction. The lowest energy Mn2(CS)2(CO)6structures are predicted have a single four-electron donor bridging η2-μ-CS group and a formal MnMn double bond. However, at only slightly higher energies, Mn2(CS)2(CO)6structures are found with two η2-μ-CS groups and a formal Mn–Mn single bond. A formal MnMn triple bond of length 2.36 ± 0.03 is found in an even higher energy unbridged Mn2(CS)2(CO)6structure, similar to the lowest energy Mn2(CO)8structure found in a previous theoretical study. The lowest energy structures for Mn2(CS)2(CO)5have two η2-μ-CS groups and a formal MnMn double bond of length 2.57 ± 0.03 . [ABSTRACT FROM AUTHOR]

Theoretical studies on Co2(CO)6(PX)2derivatives (X = H, Cl, OH, OMe, NH2, NMe2) predict the lowest energy structures to be butterfly structures containing five two-electron two-center bonds in the central Co2P2unit. Among these butterfly structures the energy increases as the unique bond forming the “body” of the butterfly changes from Co–Co to Co–P and then P–P. Higher energy rhombus structures are also found for Co2(CO)6(PX)2with only Co–P bonds in the Co2P2framework without any Co–Co or P–P bonds. In addition, for Co2(CO)6(POR)2(R = H, Me) still higher energy “diphosphine” structures are also found containing only three rather than four Co–P bonds, one P–P bond, and no CoCo bond. For the isoelectronic Co2(CO)6S2a rhombus structure is competitive in energy with the butterfly structures with five structures lying within ∼4 kcal/mol thereby predicting a fluxional system. A tetrahedrane structure was not found for Co2(CO)6S2in contrast to the tetrahedrane structure known experimentally for the related Fe2(CO)6S2with one less electron per metal atom. [ABSTRACT FROM AUTHOR]

The first structural characterization of the highly unsaturated octacarbonyldivanadium, V 2 (CO) 8 , is reported using density functional theory (DFT) with the B3LYP and BP86 functionals. Various combinations of vanadium–vanadium multiple bonding, four-electron bridging CO groups, and metal electron configurations less than the 18-electron rare gas configuration are found to accommodate the high unsaturation implied by the V 2 (CO) 8 stoichiometry. Thus, the global minimum for V 2 (CO) 8 is a C 2h structure (1) with two four-electron bridging CO groups and a vanadium–vanadium distance of 2.896 (B3LYP) or 2.858?Å (BP86), suggestive of a V–V single bond and thus 16-electron configurations for the vanadium atoms. The next lowest-lying structure (2) for V 2 (CO) 8 at 10.6 (B3LYP) or 12.5?kcal?mol -1 (BP86) above the global minimum (1) also has C 2h symmetry with two bridging CO groups, but a much shorter vanadium–vanadium distance of 2.440 (B3LYP) or 2.460?Å (BP86), suggestive of a V=V triple bond. Of similar energy to 2 is a D 4d unbridged structure (3) for V 2 (CO) 8 with an extremely short vanadium–vanadium distance of 1.941 (B3LYP) or 1.967?Å (BP86), consistent with, but not proving, the presence of the quintuple bond required to give each vanadium atom the favored 18-electron rare gas electronic configuration. The one other optimized structure for V 2 (CO) 8 within 27?kcal?mol -1 of the global minimum and without any imaginary vibrational frequencies is a highly unsymmetrical C s structure (6) with three very unsymmetrical bridging CO groups and a vanadium–vanadium distance of 2.615 (B3LYP) or 2.509?Å (BP86), suggestive of a V=V double bond. [ABSTRACT FROM AUTHOR]

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 rhenadicarbaborane carbonyl nitrosyls (C2Bn−3Hn−1)Re(CO)2(NO), (n = 8 to 12), of interest in drug delivery agents based on the experimentally known C2B9H11Re(CO)2(NO) and related species, have been investigated by density functional theory. The lowest energy structures of these rhenadicarbaboranes are all found to have central ReC2Bn−3 most spherical closo deltahedra in accord with their 2n + 2 Wadean skeletal electrons. Carbon atoms are found to be located preferentially at degree 4 vertices in such structures. Furthermore, rhenium atoms are preferentially located at a highest degree vertex, typically a vertex of degree 5. Only for the 9-vertex C2B6H8Re(CO)2(NO) system are alternative isocloso deltahedral isomers found within ~8 kcal/mol of the lowest energy closo isomer. Such 9-vertex isocloso structures provide a degree 6 vertex for the rhenium atom flanked by degree 4 vertices for each carbon atom. [ABSTRACT FROM AUTHOR]

The heterometallic chromium-manganese carbonyl nitrosyls CrMn(NO)(CO)n (n = 9, 8) have been investigated by density functional theory. The lowest energy CrMn(NO)(CO)9 structures have unbridged staggered conformations with a ~2.99 Å Cr–Mn single bond similar to the experimental and lowest energy structures of the isoelectronic Mn2(CO)10 and Cr2(NO)2(CO)8. A significantly higher energy CrMn(NO)(CO)9 isomer has a nearly symmetrical bridging nitrosyl group and a very weakly semibridging carbonyl group. The two lowest energy structures of the unsaturated CrMn(NO)(CO)8 have a five-electron donor bridging η2-µ-NO nitrosyl group or a four-electron donor bridging η2-µ-CO group, as well as a Cr–Mn single bond of length ~2.94 Å. The next higher energy CrMn(NO)(CO)8 structure has exclusively terminal CO and NO ligands and a shorter Cr–Mn single bond of ~2.85 Å, suggesting an 18-electron configuration for the manganese atom and a 16-electron configuration for the chromium atom indicated by a vacant coordination site nearly perpendicular to the Cr–Mn bond. [ABSTRACT FROM AUTHOR]

The structures and energetics of the binuclear pentalene titanium carbonyls PnTi2(CO)n (Pn = η5,η5‐C8H6; n = 8, 7, 6, 5, 4, 3, 2) and their 1,4‐bis(triisopropylsilyl) derivatives related to experimentally studied systems have been examined by density functional theory. Geometric constraints within a η5,η5‐PnTi2 unit having exclusively pentahapto ring‐titanium bonds limit the TiTi distances to a maximum of ~3.1 Å in the PnTi2(CO)n derivatives in contrast to the cyclopentadienyl analogues Cp2Ti2(CO)n where bonding TiTi distances as long as ~3.9 Å are found. Furthermore, at least one 4‐electron donor η2‐μ‐CO group but never more than 2 such groups are found in the lowest energy PnTi2(CO)n structures. The lowest energy PnTi2(CO)n structures (n = 4, 3, 2) by margins of at least 10 kcal/mol have 2 η2‐μ‐CO groups and formal TiTi triple bonds in the singlet spin state. The carbonyl rich species PnTi2(CO)n and Pn†Ti2(CO)n (n = 8, 7) are not viable with respect to CO dissociation to give the corresponding hexacarbonyls. The structures and energetics of the binuclear pentalene titanium carbonyls PnTi2(CO)n (Pn = η5,η5‐C8H6; n = 8, 7, 6, 5, 4, 3, 2) and their 1,4‐bis(triisopropylsilyl) derivatives related to experimentally studied systems have been examined by density functional theory. Geometric constraints limit the TiTi distances to a maximum of ~3.1 Å. At least one 4‐electron donor η2‐μ‐CO group but never more than 2 such groups are found in the lowest energy PnTi2(CO)n structures. [ABSTRACT FROM AUTHOR]

Graphical abstract Fluorine shift from sulfur to the metal atom occurs in all of the low energy CpM(CO) n SF 2 NMe 2 structures (M = Cr, Mo, W) giving structures having separate Me 2 NSF and fluorine ligands. Abstract Previous theoretical studies predict metal SF 3 complexes to be disfavored relative to shift of a fluorine atom from the SF 3 ligand to the metal atom to give complexes with separate SF 2 and fluorine ligands. We now explore metal complexes of the Me 2 NSF 2 ligand hoping that substituting one of the electron-withdrawing fluorine atoms with an electron releasing dimethylamino group will strengthen the sulfur-fluorine bonds thereby inhibiting fluorine shift from sulfur to metal. The cyclopentadienylmetal carbonyl systems of the group 6 metals chromium, molybdenum, and tungsten were chosen for this study since CpM(CO) 2 SF 2 NMe 2 (M = Cr, Mo, and W) derivatives with an intact Me 2 NSF 2 ligand would be analogs of the very stable nitrosyls CpM(CO) 2 (NO). However, for all of the CpM(CO) n SF 2 NMe 2 systems fluorine shift from sulfur to the metal atom occurred in all of the low-energy structures giving structures having separate Me 2 NSF and fluorine ligands. Isomeric CpM(CO) 2 SF 2 NMe 2 structures with intact Me 2 NSF 2 ligands bonded to the metal through both sulfur and nitrogen analogous to the known metal nitrosyls CpM(CO) 2 (NO) lie 13–18 kcal/mol in energy above the lowest energy isomers with split Me 2 NSF + F ligands. [ABSTRACT FROM AUTHOR]

As an illustration of a decomposition route of metal carbonyl nitrosyls by reduction of coordinated NO groups by adjacent CO groups resulting in CO 2 liberation, the Ru 3 (CO) 10 (NO) 2 system is studied by density functional theory. Intermediates for the formation of Ru 3 (CO) 9 (µ-N 2 O) and Ru 3 (CO) 8 (µ 3 -N 2) are identified. [Display omitted] The stability of some metal carbonyl nitrosyls is limited by the oxidation of CO groups by adjacent NO groups to eliminate CO 2. Theoretical studies show how intermediates in such processes can be trapped as molecular species using the central Ru 3 unit found in the stable and experimentally known Ru 3 (CO) 10 (µ-NO) 2. Two stages of such NO reduction by adjacent CO ligands have been identified in the Ru 3 system. The first stage, as demonstrated by conversion of Ru 3 (CO) 10 (µ-NO) 2 to the N 2 O complex Ru 3 (CO) 9 (µ 3 -N 2 O), involves attack of the oxygen atom of an NO group on the carbon atom of an adjacent CO group to eliminate CO 2. This leaves a reactive nitride ligand that can couple with a second NO group to form an N 2 O complex. The oxygen atom on such an N 2 O ligand can convert an adjacent CO group to CO 2 thereby leaving behind a metal dinitrogen complex. [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]

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]

Binuclear cycloheptatrienylchromium carbonyls of the type (C7H7)2Cr2(CO)n (n = 6, 5, 4, 3, 2, 1, 0) have been investigated by density functional theory. Energetically competitive structures with fully bonded heptahapto η7-C7H7 rings are not found for (C7H7)2Cr2(CO)n structures having two or more carbonyl groups. This result stands in contrast to the related (CnHn)2M2(CO)n (M = Mn, n = 6; M = Fe, n = 5; M = Co, n = 4) systems. Most of the predicted (C7H7)2Cr2(CO)n structures have bent trihapto or pentahapto C7H7 rings and Cr≡Cr distances in the range 2.4–2.5 Å suggesting formal triple bonds. In some cases rearrangement of the heptagonal C7H7 ring to a tridentate cyclopropyldivinyl or tridentate bis(carbene)alkyl ligand is observed. In addition structures with CO insertion into the C7H7–Cr bond are predicted for (C7H7)2Cr2(CO)n (n = 6, 4, 2). The global minima found for the (C7H7)2Cr2(CO)n derivatives for n = 6, 5, and 4 are (η5-C7H7)(OC)2Cr≡Cr(CO)4(η1-C7H7), (η3-C7H7)(OC)2Cr≡Cr(CO)3(η2,1- C7H7), and (η5-C7H7)2Cr2(CO)4, respectively. The global minima for (C7H7)2Cr2(CO)n (n = 3, 2) have rearranged C7H7 groups. Singlet and triplet structures with heptahapto η7-C7H7 rings are found for the dimetallocenes (η7-C7H7)2Cr2(CO) and (η7-C7H7)2Cr2, with the singlet structures being of much lower energies in both cases. [Copyright &y& Elsevier]

The article analyzes the characteristic of unsaturation in trinuclear metal carbonyl clusters. The author uses density functional theory (DFT) methods to examine the relative energies of three types of structures for Fe3(CO)12. The unsaturated species Fe3(CO)n (n = 12, 11, 10, 9) are similarly examined in order to determine whether their most favorable isomers use metal-metal multiple bonding.

• Low-energy (Me 2 C 2 N 2 P) 2 Ru 2 (CO) n (n = 4, 3) structures typically have dihapto bridging diazaphospholyl ligands. • Terminal η5-Me 2 C 2 N 2 P ligands or bridging η5,η1-Me 2 C 2 N 2 P ligands are found in some higher energy structures. • The (Me 2 C 2 N 2 P) 2 Fe 2 (CO) n (n = 4, 3) systems have complicated potential energy surfaces with higher spin state structures. The structures and energies of the (Me 2 C 2 N 2 P) 2 Ru 2 (CO) n (n = 4, 3) complexes of the four isomeric diazaphospholyl ligands have been studied by density functional theory. Most of the low-energy structures in these systems have one or both diazaphospholyl rings bridging a central Ru Ru bond through Ru N and/or Ru P bonds without involvement of the other three ring atoms. A few higher energy structures are found in these systems having either terminal pentahapto η5-Me 2 C 2 N 2 P ligands or bridging η5,η1-Me 2 C 2 N 2 P ligands bonded to one ruthenium atom as a pentahapto ligand and to the other ruthenium atom through a P → Ru or N → Ru dative bond. The potential surfaces of the analogous iron systems (Me 2 C 2 N 2 P) 2 Fe 2 (CO) n (n = 4, 3) are complicated considerably by other triplet and even quintet structures of comparable energies to structures analogous to the low-energy ruthenium structures. This relates to the lower ligand field strengths of iron complexes as compared with their ruthenium analogues. [Display omitted] [ABSTRACT FROM AUTHOR]

The complete series of binuclear pentalene titanium carbonyls Pn 2 Ti 2 (CO) n and Pn † 2 Ti 2 (CO) n (Pn = pentalene; Pn † = 1,4-( i Pr 3 Si) 2 C 8 H 4 ; n = 0, 1, 2, 3, 4), including Pn † 2 Ti 2 (CO) 2 obtained experimentally from Pn † 2 Ti 2 and carbon dioxide, have been investigated by density functional theory. For the carbonyl-free Pn 2 Ti 2 system the singlet structure is found to lie 22.5 and 18.5 kcal/mol in energy below the isomeric triplet and quintet structures, respectively. However, for the experimentally known Pn † 2 Ti 2 system (Pn † = 1,3-( i Pr 3 Si) 2 C 8 H 4 ) the singlet, triplet, and quintet spin state structures have essentially equal energies within 0.3 kcal/mol suggesting the possibility of complicated magnetic behavior. The Ti–Ti distance of 2.399 Å found in crystalline Pn † 2 Ti 2 by X-ray crystallography is closest to the 2.415 Å Ti-Ti distance predicted for the triplet spin state structure. Carbonylation of Pn 2 Ti 2 results in successive lengthening of the Ti-Ti distance as CO groups are added. Three CO groups are the maximum number that can be introduced into a viable Pn 2 Ti 2 (CO) n derivative as indicated by the predicted exothermic CO dissociation energy of the tetracarbonyl Pn 2 Ti 2 (CO) 4 . The lowest energy structure for the monocarbonyl Pn 2 † Ti 2 (CO) has a four-electron donor bridging η 2 -μ-CO group in accord with the experimental structure. The lowest energy structure for the dicarbonyl Pn † 2 Ti 2 (CO) 2 has exclusively terminal CO groups in a cis configuration, again in accord with the experimental Pn † 2 Ti 2 (CO) 2 structure. Two terminal CO groups are accompanied by a third highly unsymmetrical semibridging CO group in the lowest energy structures for the tricarbonyls Pn 2 Ti 2 (CO) 3 and Pn † 2 Ti 2 (CO) 3 . However, the lowest energy structures for the tetracarbonyls Pn 2 Ti 2 (CO) 4 and Pn † 2 Ti 2 (CO) 4 have exclusively terminal CO groups. [ABSTRACT FROM AUTHOR]

Metal complexes of the 2,4-di- t- butyl-1,3-diphosphacyclobutadiene ligand have been synthesized by head-to-tail dimerization of t- BuC P: on transition metal sites. In this connection the geometries and energetics of the complete series of binuclear cobalt carbonyl complexes (Me 2 C 2 P 2 ) 2 Co 2 (CO) n ( n = 5, 4, 3, 2, 1) of the simpler 2,4-dimethyl-1,3-diphosphacyclobutadiene ligand have been investigated by density functional theory. The lowest energy structures of these complexes have bridging η 4 ,η 1 -Me 2 C 2 P 2 ligands donating six electrons to the central Co 2 unit through a tetrahapto ring-metal linkage to one cobalt atom and a phosphorus lone pair to the other cobalt atom. For the tetracarbonyl (Me 2 C 2 P 2 ) 2 Co 2 (CO) 4 doubly CO-bridged structures with terminal η 4 -Me 2 C 2 P 2 ligands similar to known (η 5 C 5 H 5 ) 2 Fe 2 (μ-CO) 2 (CO) 2 and (η 4 -Me 4 C 4 ) 2 Co 2 (μ-CO) 2 (CO) 2 structures lie only ∼5 kcal/mol in energy above the η 4 ,η 1 -Me 2 C 2 P 2 bridged structures. For the unsaturated (Me 2 C 2 P 2 ) 2 Co 2 (CO) 3 and (Me 2 C 2 P 2 ) 2 Co 2 (CO) 2 systems, structures with one or two bridging η 4 ,η 1 -Me 2 C 2 P 2 ligands, respectively, are preferred energetically over isomeric structures with formal Co Co double bonds and Co Co triple bonds, respectively. The lowest energy structure for the monocarbonyl (Me 2 C 2 P 2 ) 2 Co 2 (CO) is a triplet structure in which a (Me 2 C 2 P 2 ) 2 Co sandwich unit functions as a tridentate ligand to a CoCO unit through a phosphorus atom on each ring as well as the central cobalt atom. [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]

The structures and thermodynamics of the binuclear phospholyl iron carbonyls (C 4 H 4 P) 2 Fe 2 (CO) n ( n = 6, 5, 4, 3, 2) have been investigated using density functional theory. The low-energy (C 4 H 4 P) 2 Fe 2 (CO) n ( n = 4, 3, 2) structures are found to have direct iron–iron bonds and terminal five-electron donor pentahapto η 5 -C 4 H 4 P rings with the phosphorus lone pairs not involved in the bonding to the iron atoms. They are thus analogous to the corresponding cyclopentadienyliron carbonyl derivatives. However, they differ from the binuclear phospholyl manganese carbonyls (C 4 H 4 P) 2 Mn 2 (CO) n ( n = 5, 4) for which structures with bridging seven-electron donor η 5 , η 1 -C 4 H 4 P phospholyl rings are the lowest energy structures by substantial margins. Partially bonded phospholyl rings, as well as direct Fe–Fe bonds, are found in the carbonyl-rich (C 4 H 4 P) 2 Fe 2 (CO) n ( n = 6, 5) species. The pentacarbonyl (C 4 H 4 P) 2 Fe 2 (CO) 5 does not appear to be a viable species since it is disfavored relative to CO loss and to disproportionation into (C 4 H 4 P) 2 Fe 2 (CO) 6 + (C 4 H 4 P) 2 Fe 2 (CO) 4 . [ABSTRACT FROM AUTHOR]

The structures and energetics of the binuclear ruthenium carbonyl nitrosyls Ru 2 (NO) 2 (CO) n ( n = 7, 6, 5, 4) have been studied by density functional theory for comparison with the isovalent Fe 2 (NO) 2 (CO) n and Rh 2 (CO) n +2 systems. The lowest energy Ru 2 (NO) 2 (CO) 6 structure has two bridging NO groups analogous to the lowest energy Fe 2 (NO) 2 (CO) 6 and Rh 2 (CO) 8 structures, which are also doubly bridged structures. The lowest energy Ru 2 (NO) 2 (CO) 5 structures are two nearly degenerate structures. One of these structures has a single bridging NO group. The other low energy Ru 2 (NO) 2 (CO) 5 structure and the lowest energy Ru 2 (NO) 2 (CO) 4 structure have semibridging NO and CO groups. The energetics of the Ru 2 (NO) 2 (CO) n ( n = 6, 5, 4) systems indicate the preference for bridging NO groups relative to bridging CO groups in otherwise equivalent structures. In addition, Ru 2 (NO) 2 (CO) 5 is disfavored relative to disproportionation into Ru 2 (NO) 2 (CO) 6 + Ru 2 (NO) 2 (CO) 4 . The lowest energy structure of the carbonyl-rich Ru 2 (NO) 2 (CO) 7 , like that of Ru 2 (NO) 2 (CO) 6 , has two bridging NO groups but a long Ru⋯Ru distance greater than 3.3 Å indicating the lack of a direct Ru–Ru bond. However, this Ru 2 (NO) 2 (CO) 7 structure is disfavored relative to both CO loss and fragmentation into Ru(NO) 2 (CO) 2 + Ru(CO) 5 . [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]

Densityfunctional theory confirms the experimentally known triplybridged Rh4(CO)9(μ-CO)3structureto be the lowest-energy structure. The lowest-energy structures ofthe unsaturated systems Rh4(CO)n(n= 11, 10, 9, 8) are also triply bridged structureswith central Rh4tetrahedra that can be derived from thisRh4(CO)9(μ-CO)3structure byremoval of terminal CO groups in various ways. The MM distancesin these central M4tetrahedra change very little as COgroups are lost, suggesting reluctance to form metal–metalmultiple bonds in these unsaturated systems. The natural bond orbital(NBO) Wiberg bond indices provide depth to this analysis. All of theseunsaturated systems are predicted to be highly fluxional, as two tothree isomeric structures lie within ∼4 kcal/mol of the globalminima. The Rh4(CO)8(μ-CO)2(μ4-CO) structure analogous to the lowest-energyCo4(CO)11structure with all four atoms of acentral Co4butterfly bridged by a μ-CO group ispredicted to lie ∼6 kcal/mol in energy above the lowest-energyRh4(CO)11structure. Comparisons of the relativeenergies of analogous Rh4(CO)nand Ir4(CO)nstructures indicatethat more highly bridged M4(CO)nstructures are energetically much more favorable for rhodium thanfor iridium. Dissociation energies (for loss of CO) and disproportionationenergies are reported. [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 lowest energy structures of the unsaturated Co 4 (CO) n ( n = 10, 9) clusters, potentially obtained by decarbonylation of the known Co 4 (CO) 12 , are predicted by density functional theory (DFT) to have central Co 4 butterflies with five bonding Co–Co interactions rather than Co 4 tetrahedra with six bonding Co–Co interactions. Both face-bridging μ 3 -CO and edge-bridging μ -CO groups are found in such structures. Slightly higher energy Co 4 (CO) n ( n = 10, 9) butterfly structures are found with a unique μ 4 -CO group bridging all four cobalt atoms similar to the lowest energy Co 4 (CO) 11 structure from a previous DFT study. The lowest energy Co 4 (CO) n ( n = 10, 9) structures differ significantly from their Ir 4 (CO) n analogues, which mainly have central Ir 4 tetrahedra rather than Ir 4 butterflies and only one or two edge-bridging μ -CO groups. [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]

Reactions of acetylene, thiophene, or even tellurophene with iron carbonyls have been found to give the tricarbonylferrole iron tricarbonyl, [η4-C4H4Fe(CO)3]Fe(CO)3, which has been shown by X-ray crystallography to contain a metallacyclic FeC4 ring with an Fe–Fe bonding distance of ∼2.5Å to the exocyclic iron atom. This structure has been shown by density functional theory to be the lowest energy C4H4Fe2(CO)6 structure by more than 30kcal/mol relative to the lowest energy isomeric triplet structure. Dissociation of carbonyl groups from this structure requires ∼40kcal/mol per carbonyl group. The central C4H4Fe2 unit in the resulting unsaturated C4H4Fe2(CO) n (n =5, 4, 3) structures is relatively rigid upon carbonyl loss with the Fe–Fe distance decreasing only to ∼2.4Å in even the highly unsaturated C4H4Fe2(CO)3. Thus 16-electron metal configurations with iron–iron single or double bonds rather than the normally favored 18-electron metal configurations are preferred over structures with higher order iron–iron multiple bonds. For the carbonyl-rich species the lowest energy C4H4Fe2(CO)8 structure has one C C double bond of a tetracarbonylferrole ring bonded to an exocyclic Fe(CO)4 moiety with a long Fe⋯Fe non-bonding distance of ∼3.8Å. The low-energy structures for C4H4Fe2(CO)7 either have a dihapto ferrole ligand with an iron–iron bond or a tetrahapto ferrole ligand without an iron–iron bond. However, C4H4Fe2(CO)7 does not appear to be viable since carbonyl dissociation from the lowest energy C4H4Fe2(CO)7 structure to give C4H4Fe2(CO)6 is predicted to be an exothermic process. [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]

The structures and energetics of the cyclobutadiene manganese carbonyls (C4H4)2Mn2(CO) n (n =6, 5, 4, 3) have been investigated using density functional theory. In this connection the lowest energy (C4H4)2Mn2(CO)6 structure consists of two C4H4Mn(CO)3 units coupled through an Mn–Mn bond of length ∼3.0Å. This rather fragile dimer is predicted to dissociate readily into C4H4Mn(CO)3 radicals. A higher energy (C4H4)2Mn2(CO)6 structure has an agostic hydrogen atom and an Mn⋯Mn distance of ∼4.3Å, too long for a direct bond. The unsaturated pentacarbonyl (C4H4)2Mn2(CO)5 system resembles its (C5H5)2Cr2(CO)5 counterpart by having low energy triplet spin state structures and being disfavored relative to (C4H4)2Mn2(CO)6 +(C4H4)2Mn2(CO)4. A singlet tetracarbonyl (C4H4)2Mn2(CO)4 structure is found with a short Mn Mn distance of ∼2.2Å suggesting a formal triple bond analogous to the known (C5H5)2Cr2(CO)4 structure. However, the lowest energy (C4H4)2Mn2(CO)4 state is a novel triplet spin state octahedral Mn2C4 cluster with Mn(CO)3 and (η4-C4H4)Mn(CO) vertices. The lowest energy (C4H4)2Mn2(CO)3 structure by ∼13kcal/mol is an unsymmetrical triplet spin state structure with a C4H4 ligand bridging a dative formal Mn Mn triple bond connecting an Mn(CO)3 group to a (η4-C4H4)Mn group. [ABSTRACT FROM AUTHOR]