C-H Activation of Benzene by a Photoactivated NiII(azide): Formation of a Transient Nickel Nitrido Complex

Photochemical activation of nickel-azido complex 2 [Ni(N-3)(PNP)] ((PNP)-P-H= 2,2'-di(isopropylphosphino)-4,4'-ditolylamine) in neat benzene produces diamagnetic complex 3 [Ni(Ph)((PNNH)-N-P)], which is crystallographically characterized. DFT calculations support photoinitiated N-2-loss of the azido complex to generate a rare, transient Ni-IV nitrido species, which bears significant nitridyl radical character. Subsequent trapping of this nitrido through insertion into the Ni - P bond generates a coordinatively unsaturated NiII imidophosphorane P= N donor. This species shows unprecedented reactivity toward 1,2-addition of a C-H bond of benzene to form 3. The structurally characterized chlorido complex 4 [Ni(Cl)-((PNNH)-N-P)] is generated by reaction of 3 with HCl or by direct photolysis of 2 in chlorobenzene. This is the first report of aromatic C-H bond activation by a trapped transient nitrido species of a late transition metal.