Synthesis, Electronic Structure, and Reactivity of a Planar Four-Coordinate, Cobalt–Imido Complex

A four-coordinate cobalt–imido complex, (^tBumPNP)Co=NMes (^tBumPNP=modified PNP pincer ligand) has been synthesized from addition of 2,4,6-trimethylphenylazide (Mes–N₃) to the corresponding dinitrogen complex. The solid-state structure determined by X-ray diffraction established a rare, idealized planar geometry with a Co=N bond distance of 1.716(2) Å. Magnetic measurements revealed an S=1 ground state with CAS-SCF calculations supporting radical character on the imide nitrogen. Thermolysis of the cobalt–imido compound induced selective insertion of the imido group into a Co−P bond and yielded a three-coordinate cobalt complex with a distorted T-shaped geometry. Transition state analysis conducted with DFT calculations established the thermodynamic stability of the P–N coupled product and provided insight into the exclusive selectivity.