AN INTERPRETATION OF ORGANOMETALLIC BOND-DISSOCIATION ENERGIES

Organometallic bond dissociation energies (BDE) are incorporated into the E and C model with excellent results. Since the data are consistent with gas-phase systems, the fit supports claims that the enthalpies are relatively free of solvation contributions. The organometallic catimers (fragments forming the positive end of the dipole) include (CO)5MnI, [eta-5-(CH3)3SiC5H4]3UIV-, [eta-5-C5H5](CO)3MoII5-, [eta-5-C5(CH3)5][P(CH3)3](H)IrIII-, [eta-5-C5(CH3)5]2(CH3)3CO]ThIV-, [eta-5-(CH3)5][P(CH3)3]2RuII-, [(C6H5)2PCH2CH2P(C6H5)2](CH3)PtII-, [eta-5-C5(CH3)5]2Zr-, and 1/2[eta-5-[C5(CH3)5]2Sm]2-. The animers (fragments forming the negative end of the dipole) include organics, halogens, and inorganics. In addition to predicting and interpreting enthalpies, the resulting parameters for the radicals provide reactivity scales that can be used to interpret reactivity and physicochemical properties. Significant chemical insight results from the fit of the data to the ECT model. The parameters are used to reinterpret F-19 chemical shifts in (F-Ph)Pt(P2R3)2-X, in terms of a sigma-only Pt-X bond. The earlier interpretation is one of the classic examples used to support metal-ligand pi-bonding interactions. Predicted bond energies are analyzed to indicate the metal properties that facilitate the CO insertion reaction. The analysis provides insights into the relative importance of electrostatic and covalent interactions. Further, the analysis shows that simply plotting the data of L(n)M-X versus H-X gives an incomplete and potentially incorrect interpretation of the data. Another outcome of the analysis is that certain data points are brought into question as well as suggestions for key experiments needed to bring better insight into several systems.