How Do the Electronic Structures of Low-Symmetry Metal−Hydride and −Alkyl Complexes Compare? Photoelectron Spectroscopy and Computational Studies of (η5-C5R5)Re(NO)(L)R‘ (L = CO, P(C6H5)3; R, R‘ = H, CH3)

Abstract

The electronic structures of CpRe(NO)(L)R and Cp*Re(NO)(L)R (Cp = η5-C5H5, Cp* = η5-C5(CH3)5; L = CO, P(C6H5)3; R = H, CH3) are studied using gas-phase photoelectron spectroscopy and density functional theory. Separate valence ionizations from the three occupied metal-based orbitals of the d6 Re center, the Re−R σ bond orbitals, and the predominantly Cp e1‘ ‘ pπ orbitals are clearly observed. Comparison of the shapes and energies of the Cp and σ(Re−R) ionizations indicates an additional direct interaction between these orbitals that is sensitive to energy matching. This interaction results in a more delocalized σ-bonding framework for the methyl complexes than for the analogous hydrides and halides. The energy shifts and cross-sections of the metal-based ionizations provide quantitative measures of the different abilities of the nitrosyl, carbonyl, and phosphine ligands to delocalize and stabilize the metal electron density through π back-bonding. In these molecules the stabilization of a metal-based ioni...