Electron inductive perturbation(s) of heteronuclear metal–metal bonds. Isocyanide and indenyl derivatives of the mixed metal dimers [(η5–C5H5)Fe(CO)2Re(CO)5] and [MnRe(CO)10]

Abstract

The properties of the heteronuclear metal–metal bonds in the unbridged [η5–C5H5)Fe(CO)2Re(CO)5−n(CNR)n] and [(η5–C9H7)Fe(CO)2Re(CO)5−n(CNR)n complexes (n = 0, 1, 2; R = tert-butyl (tBu) and 2,6-dimethylphenyl (Xy)) and the two equatorially substituted isomers of [MnRe(CO)8(CN-tBu)2] have been investigated theoretically by Extended Hückel Molecular Orbital calculations (EHMO) and experimentally by UV–visible spectroscopy, electrochemistry, and by microRaman or FT-Raman spectroscopy. The expected dσ* orbital is the lowest unoccupied molecular orbital (LUMO), mainly fabricated by interactions of the metal [Formula: see text] orbital, but the dπ* and dσ orbitals are the highest occupied molecular orbital (HOMO) and HOMO-1, respectively, as demonstrated experimentally from the UV–visible spectra. The EHMO computations demonstrate the mixing between these two dπ* (and dδ) and dσ MO orbitals. The influence of substituent effects on the spectroscopic and electrochemical properties is complicated and is interpreted in terms of inductive effects and relative destabilisation of the dσ, dπ*, and dσ* molecular orbitals. Finally, the metal–metal stretching frequencies for four mixed metal dimers (MnRe and FeRe) are reported.