Quantum‐Chemical Investigations of Stabilizing Interactions in μ‐Diborylcarbene Dicobalt Complexes with a Planar Tetracoordinate Carbon Atom

Quantum‐chemical methods have been employed to study the nature of stabilization in dinuclear cobalt complexes of the general formula [{(C 5 H 5 )Co} 2 (μ‐CR 1 2 BCBR 2 R 3 )] ( 6 ) as well as the “antivan't Hoff–Le Bel” configuration of the planar tetracoordinate carbon (ptC) atom of the bridging diborylcarbene ligand 9 . Extended Hückel and ab initio Hartree‐Fock calculations have been carried out for the model compounds 6b (R 1 = R 2 = R 3 = H) and 6c (R 1 = R 2 = H; R 3 = C 6 H 5 ). Ab initio electron deformation density maps and natural population analysis calculations show that complexes 6 are stabilized through push–pull effects by which the ptC experiences π electron density delocalization and σ electron density accumulation. The calculated electronic configuration of the ptC in the free ligand 9b is σ 2.978 π 1.501 , and in 6b σ 3.944 π 1.356 . Electron density donation from one cobalt atom to an aryl group on the bridging ligand further contributes to the stabilization of the complexes 6 .