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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]

Density functional theory studies show that the lowest energy C4F8Fe(CO)4 structure is not the very stable experimentally known ferracyclopentane isomer (CF2CF2CF2CF2)Fe(CO)4 obtained from Fe(CO)12 and tetrafluoroethylene. Instead isomeric (perfluoroolefin)Fe(CO)4 structures derived from perfluoro-2-butene, perfluoro-1-butene, and perfluoro-2-methylpropene are significantly lower energy structures by up to ∼17 kcal mol−1. However, the activation energies for the required fluorine shifts from one carbon to an adjacent carbon atom to form these (perfluoroolefin)Fe(CO)4 complexes from tetrafluoroethylene are very high (e.g., ∼70 kcal mol−1). Therefore the ferracyclopentane isomer (CF2CF2CF2CF2)Fe(CO)4, which does not require a fluorine shift to form from Fe3(CO)12 and tetrafluoroethylene, is the kinetically favored product. The lowest energy structures of the binuclear (C4F8)2Fe2(CO)n (n = 7, 6) derivatives have bridging perfluorocarbene ligands and terminal perfluoroolefin ligands. [ABSTRACT FROM AUTHOR]

The geometries and energetics of tritungstaboranes Cp3W3(H)Bn−3Hn−3 (Cp = η5-C5H5; n = 5 to 12), related to the experimentally known Cp*3W3(H)B8H8 (Cp* = η5-Me5C5), have been investigated using density functional theory and coupled cluster calculations. Such low-energy structures have central W3Bn−3 deltahedra with superimposed bonded W3 triangles. The “extra” hydrogen atom either bridges a deltahedral edge or caps a deltahedral face containing at least one tungsten atom. The tungsten atoms are located at degree 5 to 7 vertices in regions of a relatively low surface curvature whereas the boron atoms are located at degree 3 to 5 vertices in regions of a relatively high surface curvature. The five lowest-energy structures of the 11-vertex tritungstaborane Cp3W3(H)B8H8 all have the same central W3B8 deltahedron and differ only by the location of the “extra” hydrogen atom. The isosceles W3 triangles in these structures have two long ∼3.0 Å W–W edges through the inside of the deltahedron with the third shorter W–W edge of ∼2.7 to ∼2.8 Å corresponding to a surface deltahedral edge. The five Cp3W3(H)B8H8 structures differ only by the location of the “extra” hydrogen atom. The lowest energy such structure has the “extra” hydrogen atom bridging the surface W–W bond and corresponds to the experimental Cp*3W3(H)B8H8 structure, as determined using X-ray crystallography. [ABSTRACT FROM AUTHOR]

The unexpected 2004 discovery of decamethyldizincocene suggested some new possibilities for organometallic compounds in which an M2 unit is sandwiched between two planar carbocyclic rings. Density functional theory shows that the low-energy structures for the dizincocenes Zn2(C5X5)2 (X = H, F) are singlet coaxial structures having two (η5-C5X5)Zn units linked by a Zn–Zn single bond of length ∼2.3 Å. However, the low-energy M2(C5H5)2 (M = Cu, Ni, Co, Fe) structures have perpendicular configurations with bridging C5H5 ligands. They exhibit increasingly higher spin states from singlet (Cu, Ni) to triplet (Ni,Co), quintet (Co,Fe), and septet (Fe). The low-energy structures of the perfluorinated systems M2(C5F5)2 (M = Co, Fe) have irregular geometries with one bent bridging C5F5 ring and one planar terminal pentahapto η5-C5F5 ring, with the metal atom bearing the terminal η5-C5F5 ligand has the favored 18-electron configuration while the other metal atom has only a lower electron configuration and vacant coordination sites. [ABSTRACT FROM AUTHOR]

The experimentally known CpFeMn(CO)7 system as well as the related unsaturated CpFeMn(CO)n systems (n = 6, 5) have been investigated by density functional theory. For CpFeMn(CO)7 unbridged and doubly bridged structures with a heteronuclear Fe–Mn single bond lie within ∼5 kcal mol−1 of each other with the experimentally known unbridged structure being the lower energy structure. The three lowest-energy unsaturated CpFeMn(CO)6 structures, lying within ∼1 kcal mol−1 of each other, have very diverse structural features. The lowest-energy CpFeMn(CO)6 structure contains an unusual three-center two-electron C–H–Mn bond involving an agostic hydrogen of the Cp ring. Another such structure is a triply bridged triplet CpFe(μ-CO)3Mn(CO)3 closely related to the experimentally known Cp2Fe2(μ-CO)3 having a central UGRAPHIC DISPLAY="INLINE" ID="UGT2" SRC="UGT2"/ Fe=Mn double bond containing the two unpaired electrons of the triplet spin state. The third low-energy CpFeMn(CO)6 structure is a CpFe(CO)Mn(CO)4(η2-μ-CO) structure with a four-electron donor bridging η2-μ-CO group similar to that found in the lowest energy Mn2(CO)9 structure. The lowest-energy structure of the even more unsaturated CpFeMn(CO)5 has a short Fe≡Mn distance of only ∼2.2 Å suggesting a formal triple bond. Higher energy CpFeMn(CO)5 structures have a four-electron donor η2-μ-CO group in addition to a formal Fe=Mn double bond. The CpFeMn(CO)5 structure in which the oxygen atom of the η2-μ-CO group is bonded to manganese lies ∼9 kcal mol−1 in energy below the isomeric structure in which the oxygen of the η2-μ-CO group is bonded to iron. [ABSTRACT FROM AUTHOR]

The interaction of carbon monoxide with organoactinides has recently been shown experimentally, particularly by Cloke and co-workers, to result in coupling to give the oligomeric anions CnOn2− (n = 2, 3, 4). In order to model possible intermediates in reactions of this type, we have used density functional theory to explore the systems (C8H8)Th(CO)n (n = 1 to 5) and (C8H8)2Th2(CO)n (n = 2 to 7) related to the known “thorocene”, (η8-C8H8)2Th. Thorium was chosen as the actinide for this work since its chemistry almost entirely involves the single diamagnetic +4 oxidation state. All of the binuclear (C8H8)2Th2(CO)n structures found in this work have long Th…Th distances ranging from 4.4 to 5.0 Å suggesting the absence of direct Th–Th bonds. Two (C8H8)2Th2(CO)2 isomers of similar energies in which the two CO groups have coupled to form trans and cis isomers of a bridging η4-μ-C2O2 ligand are low energy structures. These bridging η4-μ-C2O2 ligands exhibit ultralow ν(CO) frequencies around 1000 cm−1 indicating strong back donation of thorium d and f electrons into C–O antibonding orbitals. Most of the carbonyl richer (C8H8)2Th2(CO)n (n = 3 to 7) structures are derived from one of these basic (C8H8)2Th2(CO)2 structures by addition of terminal CO groups. An exception is the lowest energy (C8H8)2Th2(CO)4 structure which has C4v symmetry with four equivalent separate η2-μ-CO groups bridging the thorium atoms. The thermochemistry of these systems suggest (C8H8)Th(CO)4 and (C8H8)2Th2(CO)n (n = 2, 4) to be the most promising synthetic objectives, which are potentially obtainable by reductive carbonylation of the known (C8H8)ThCl2. [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]

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]

The chemistry of trinuclear osmium carbonyl hydrides is a rich area with the three H2Os3(CO)n derivatives (n = 12, 11, 10) all being known stable compounds ultimately obtained from Os3(CO)12 and hydrogen under various conditions. Density functional theory studies on the H2Os3(CO)n systems (n = 12, 11, 10, 9, 8) correctly predict the structures previously reported experimentally for n = 12, 11, and 10. These include a linear structure for H2Os3(CO)12 and triangular structures for H2Os3(CO)11 and H2Os3(CO)10. However, the H2Os3(CO)11 system is predicted to be a fluxional system with the four low energy isomers lying within 2 kcal mol−1 of energy. Three of these H2Os3(CO)11 isomers, all with one terminal hydrogen and one bridging hydrogen, have been observed experimentally by NMR. In addition, the lowest energy isomer has been isolated and structurally characterized by X-ray crystallography. In contrast to H2Os3(CO)11, the lowest energy H2Os3(CO)10 structure, namely the known structure with an Os=Os edge bridged by both hydrogen atoms and all terminal CO groups, lies ∼10 kcal mol−1 below the next lowest energy isomer. The predicted CO dissociation energies of the H2Os3(CO)n derivatives (n = 12, 11, 10) suggest this H2Os3(CO)10 structure to be the “thermodynamic sink” in the H2Os3(CO)n systems, consistent with its synthesis from Os3(CO)12 and H2 at 120 °C and atmospheric pressure. The lowest energy structures of the more highly unsaturated H2Os3(CO)n (n = 9, 8) can be derived from this (μ-H)2Os3(CO)10 structure by removal of CO groups from the osmium atom remote to the doubly bridged Os=Os edge of the Os3 triangle, with relatively little change in the central (μ-H)2Os3 triangle geometry. [ABSTRACT FROM AUTHOR]

The tetramethyleneethane (TME) iron carbonyl derivative cis-(η3,η3-TME)Fe2(CO)6 has long been known as a product from the reaction of allene with iron carbonyls. Theoretical studies on the (TME)Fe2(CO)6 system show this experimentally observed singlet cis bis(allyl) structure with an Fe–Fe bond length of ∼2.9 Å to be the lowest energy structure. However, three other singlet (TME)Fe2(CO)6 structures lying in energy within 10 kcal mol−1 of this global minimum exhibit different modes of bonding of the TME ligand to the Fe2(CO)6 unit including cis and trans bis(butadiene) structures and a trans bis(trimethylenemethane) structure. The lowest energy structure for the heptacarbonyl (TME)Fe2(CO)7 has four TME carbon atoms bonded to an Fe(CO)3 unit as a butadiene ligand with the remaining two TME carbon atoms forming a five-membered FeC4 chelate ring. The lowest energy (TME)Fe2(CO)8 structure has one Fe(CO)4 unit bonded to a TME C=C double bond and the other Fe(CO)4 unit bonded to two external TME carbon atoms to form a five-membered FeC4 chelate ring thereby leaving an uncomplexed C=C double bond. The octacarbonyl (TME)Fe2(CO)8 is disfavored relative to CO loss to give the heptacarbonyl (TME)Fe2(CO)7. The heptacarbonyl is marginally viable with a low but endothermic CO dissociation energy of ∼11 kcal mol−1 to give the hexacarbonyl (TME)Fe2(CO)6. This thermochemistry can account for the experimental observation of the hexacarbonyl (TME)Fe2(CO)6 rather than carbonyl richer species as products from the reactions of allene with iron carbonyls. [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]