Metal-carbon bonding in perfluoroethylene and perfluorobenzene transition metal complexes. Some underappreciated π- and σ-acceptor components

The donor/acceptor components of metal-carbon bonds between perfluorinated ethylene (η 2 -C 2 F 4 ), or perfluorobenzene (η 6 -C 6 F 6 ), in representative transition metal complexes have been evaluated using density functional theory, coupled with energy decomposition analysis (EDA) and natural orbitals for chemical valence (NOCV). Comparisons to their hydrocarbon analogs have also been made. Two families of compounds were studied; ML 2 (η 2 -C 2 X 4 ) [ M =Ni, Pd, Pt; L =CO, PH 3 , L 2 =1,2-bis(dimethylphosphino)ethane; X =F, H] and ML 3 (η 6 -C 6 X 6 ) [ M =Cr, Mo, W; L =CO, PH 3 , L 3 =η 6 -C 6 H 6 ; X =F, H]. As expected, η 2 -C 2 F 4 is found to be a relatively weak σ-donor but a strong π-acceptor in the M-C-C plane; in addition, a mutually perpendicular π-acceptor component is revealed using EDA-NOCV. In compounds containing η 6 -C 6 F 6 , δ-backbonding dominates over π-donation and σ-donation is weak, but a significant σ-acceptor component has been revealed that is substantially stronger than σ-donation from the fluorinated ring, making η 6 -C 6 F 6 a net σ-acceptor ligand. Analogous σ-acceptor properties of hydrocarbon arenes are insignificant.