Stabilization of a Two-Coordinate Mononuclear Cobalt(0) Compound

Compound (Me-2-cAAC:)(2)Co-0 (2; Me-2-cAAC:=cyclic (alkyl) amino carbene; :C(CH2)(CMe2)(2)N-2,6-iPr(2)C(6)H(3)) was synthesized by the reduction of the precursor (Me-2-cAAC:)(2)(CoCl)-Cl-I (1) with KC8 in THF. The cyclic voltammogram of 1 exhibited one-electron reduction, which suggests that synthesis of a bent 2-metallaallene (2) from 1 should be possible. Compound 2 contains one cobalt atom in the formal oxidation state zero, which is stabilized by two Me-2-cAAC: ligands. Bond lengths from X-ray diffraction are 1.871(2) and 1.877(2) angstrom with a C-Co-C bond angle of 170.12(8)degrees. The EPR spectrum of 2 exhibited a broad resonance attributed to the unique quasi-linear structure, which favors near degeneracy and gives rise to very rapid relaxation conditions. The cAAC-Co bond in 2 can be considered as a typical Dewar-Chatt-Duncanson type of bonding, which in turn retains 2.5 electron pairs on the Co atom as nonbonding electrons.