Theoretical Studies On The Cyclopentadienyl Transition Metal Hydrides And Carbonyl Compounds

The binuclear transition metal sandwich-like chemistry is an important field for modern organometallic chemistry. Several density functional theory(DFT) methods, for example B3 LYP, BP86, MPW1PW91 and son on, are used to investigate the characters of the binuclear cyclopentadienyl transition metal hydrides and carbonyl compounds using DZP basis set. The main research results are listed as follows:(1) For the binuclear cyclopentadienyl transition metal hydrides Cp2M2Hn(M= Re, Os, Ir; Cp = η5–C5H5; n=4, 6), the lowest energy structures are predicted to have a central doubly bridged M2(μ–H)2 unit with terminal η5-Cp rings and the remaining hydrides as terminal ligands. Furthermore, for the lowest structure of Cp2Os2H4, the theoretical studies predict it to have a central quadruply bridged M2(μ–H)4 unit. For Cp2Re2H2, the lowest energy structure has one terminal η5-Cp ring, a bridging η3,η2-Cp ring, and two terminal hydride ligands bonded to the same Re atom. While for the Cp2M2H2(M = Os, Ir), the lowest energy Cp2M2H2 structures are predicted to have terminal η5-Cp rings with the central M2(μ–H)2 unit. And for the hydride-free Cp2Re2, the lowest energy isomer is a perpendicular structure with two bridging η3,η2-Cp rings and the Re–Re bond. While the lowest energy structures for Cp2Os2 and Cp2Ir2 both have one terminal η5-Cp rings and one bridging η3,η2-Cp ring.The thermochemistry of the CpReHn and Cp2Re2 Hn, CpOsHn and Cp2Os2 Hn as well as CpIr Hn and Cp2Ir2 Hn are consistent with the reported synthesis of the permethylated derivatives Cp*ReH6 and Cp*2Re2H6(Cp* = η5–Me5C5), Cp*OsH5 and Cp*2Os2H4 as well as Cp*Ir H4 and Cp*2Ir2Hn(n =2, 6) as very stable compounds, respectively. Note that Cp*ReH6, Cp*OsH5 and Cp*IrH4 all have favored 18-electron configuration for the metal atoms.Additionally, natural bond orbital analysis(NBO), atoms-in-molecules(AIM) and overlap population density-of-state in Program for Molecular Orbital Analysis(AOMIx) were all applied to present the existence of Re Re quadruple bonds in 4H-8S, formulated as σ+2π+δ type. At the same time, natural bond orbital analysis indicates the triple Os≡Os bond in 0H-1T, formulated as σ+2π type. Also, the frontier molecular orbital(HOMO) analysis suggested that a higher energy Cp2Ir2 structure 0H-4S consists of two Cp Ir units linked solely by a Ir Ir quadruple bond, formulated as 2?+2π type.(2) For the third row metal carbonyl trifluorosulfane compounds, [M](SF3)( [M] = Ta(CO)5, Re(CO)4, CpW(CO)2, CpOs(CO), Ir(CO)3 and CpPt) 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 having essentially the same energy as the lowest energy Ir(SF2)(F)(CO)3 isomer. 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.(3)Density functional theory predicts the binuclear iron carbonyl difluorosulfane derivertives Fe2(μ-SF2)2(CO)8 and Fe2(μ-SF2)(SF2)(CO)7, which are lack of direct iron-iron bonds. This theoretical study predicts the existence of viable Fe2(SF2)2(CO)n(n = 8, 7) structures having intact SF2 ligands. The Fe2(μ-SF2)2(CO)8 structure 8-1S with two bridging SF2 groups is particularly favorable since it lies more than 16 kcal/mol in energy below the next lowest energy isomer 8-2S. In addition, three low energy Fe2(μ-SF2)(SF2)(CO)7 stereoisomers having one terminal and one bridging SF2 group are found with energies within ~1 kcal/mol. This closeness in energy of three stereoisomers suggest a highly fluxional system. The bridging SF2 ligands in the three Fe2(μ-SF2)(SF2)(CO)7 structures 7-1S, 7-2S, and 7-3S are of a different type than those in 8-1S. In contrast to the binuclear Fe2(SF2)2(CO)n(n = 8, 7) derivatives, the mononuclear Fe(SF2)(CO)n(n = 4, 3) are disfavored by ~10 kcal/mol for n = 4 to ~30 kcal/mol for n = 3, respectively, with respect to fluorine shift from sulfur to iron to give the corresponding Fe(SF)(F)(CO)n derivatives. The SF ligands in the tetracarbonyls Fe(SF)(F)(CO)4 are one-electron donor ligands with Fe–S distances of ~2.3 ?. However, the SF ligands in the tricarbonyls Fe(SF)(F)(CO)3 are three-electron donor ligands with significantly shorter Fe=S distances of ~2.1 ?.(4)The cobalt(III) complexes Cp2Co2F4 and Cp2Co2(CN)4 have been studied by density functional theory methods. The lowest-energy isomers for Cp2Co2(CN)4 and Cp2Co2F4 are triplet and quintet spin state structures, respectively. Almost all of the Cp2Co2X4 structures were found to have nonbonding Co···Co distances in excess of 2.9 ?, as expected for Co(III) complexes. In general, structures with trans stereochemistry of the Cp and other terminal ligands were found to be of lower energy than the corresponding structures with cis stereochemistry.