A Theoretical Analysis of Supported Quintuple and Quadruple Chromium-Chromium Bonds

The extended transition state (ETS) energy decomposition scheme has been combined with the natural orbitals for chemical valence (NOCV) density decomposition method (ETS-NOCV) in a study on the shortest, fully supported metal-metal bond (Cr-Cr = 1.73 angstrom) in Cr-2[Ar'NC(NMe2)NAr'](2) [Ar' = C6H3-2,6(C6H3-2,6-Pr-2(i))(2)]. The scope of the ETS-NOCV method is further demonstrated by a metal-metal bond analysis of the paddlewheel M-2(O2CCH3)(4) (M = Cr, Mo, AAT) complexes. The influence of axial ligands as well as R' goups on the bridging ligands is also analyzed. In addition to the quintuple bonding components (sigma(2), pi(4), delta(4)) for Cr-2[Ar'NC(NMe2)NAr'](2) and quadruple components (sigma(2), pi(4), delta(2)) for the paddlewheel complexes, we notice additional stability (17-27 kcal/mol) introduced to the metal-metal bond from participation of the lone pairs residing on the pi-systems of the bridging X-C-X (X = N, O) ligand. This is to our knowledge the first time that the strength of the metal-metal bonding components has been determined in a supported metal-metal bond by an energy decomposition scheme.