Group-Transfer Reactions of Ni(II)−Ni(II) Bridging Imido Complexes. Catalytic Formation of Carbodiimides and Isocyanates via Nitrene Transfer from Organoazides

The NHC-supported Ni(I) dimer {(IPr)Ni(μ-Cl)} 2 ( 1; IPr = 1,3-di(2,6-di-isopropylphenyl)imidazolin-2-ylidene) yields the bridging d 8 −d 8 imido complex {(IPr)NiCl} 2 (μ-NMes) ( 2; Mes = 2,4,6-Me 3 C 6 H 2 ) upon combination with N 3 Mes. Tosylazide reacts with 1 to give the paramagnetic, dark red complex {(IPr)Ni} 2 (Cl)(μ-Cl)(μ-N,κ 1 -O:NSO 2 Tol) ( 3 ). Chloride abstraction from 2 with NaBAr F 4 affords the d 8 −d 8 dimer [{(IPr)Ni} 2 (μ-Cl)(μ-NMes)]BAr F 4 ( 4; BAr F 4 = B[3,5-(CF 3 )C 6 H 3 )] 4 ), and reduction of 2 with KC 8 yields the neutral d 8 −d 9 mixed-valence complex {(IPr)Ni} 2 (μ-Cl)(μ-NMes) ( 5 ). 2 undergoes stoichiometric nitrene group transfer to CO, PMe 3, and CNR (R = CH 2 Ph, CMe 3 ) to form MesN═C═O, MesN═PMe 3, and MesN═C═NR with regeneration of 1 . Both 1 and 2 react with excess CNR to give monomeric, three-coordinate Ni(I) complexes (IPr)NiCl(CNR) ( 6a, R = CH 2 Ph; 6b R = CMe 3 ). In the presence of excess CO, 1 undergoes disproportionation to give {(IPr)NiCl} 2 (μ-Cl) 2 ( 7 ) and (IPr)Ni(CO) 3 . Similarly, reaction of 2 with PMe 3 is accompanied by disproportionation of 1 to (IPr)NiCl 2 (PMe 3 ) ( 8 ) and [(IPr)Ni] 2 . Catalytic carbodiimide (MesN═C═NR) formation is achieved with 10 mol % 1, N 3 Mes, and CNR. Catalytic mesityl isocyanate (MesN═C═O) formation is achieved with 10 mol % 4, N 3 Mes, and CO.