Theoretical study of redox induced isomerizations, structure and bonding of nitrile, isocyanide and carbonyl complexes of rhenium

Abstract

Quantum chemical calculations at the B3LYP level of theory have been performed on the trans- and cis-isomers of nitrile, isocyanide and carbonyl phosphinic chloro-complexes and dinitrile complexes of rhenium (as well as on their mono- and dioxidized forms) trans-/cis-[ReClL(PH₃)₄]ⁿ⁺ (L = NCCH₃, CNCH₃, CO; n = 0–2) and trans-/cis-[Re(NCCH₃)₂(PH₃)₄]^m+ (m = 1–3), taken as models of the corresponding real species trans-/cis-[ReClL(dppe)₂]ⁿ⁺ (L = NCR, CNR, CO) and trans-/cis-[Re(NCR)₂(dppe)₂]^m+, allowing the interpretation of the influence of the electronic structure, of the electron π-acceptor/σ-donor character and the nature of the ligand L, and of the electron releasing/acceptor ability of the binding metal centre on the structural, spectral, chemical (towards protonation) and redox properties and on the relative stability of the geometrical isomers, thus providing also a rationale for electron-transfer induced geometrical isomerizations. For the non-oxidized forms, the cis-isomers are more stable than the respective trans-isomers for the complexes with the relatively weak π-acceptor acetonitrile ligand while for the stronger π-acceptor ligands, i.e. isocyanide and carbonyl, the latter isomers are more stable than the former. The oxidation results in the inversion of the relative stability as well as of the relative values of the ionization potentials for the trans- and cis-isomers. The nature of the coordination bond is also investigated using the natural bond orbital (NBO) method and the charge decomposition analysis (CDA).