β‑Diketiminato Nickel Imides in Catalytic Nitrene Transfer to Isocyanides

The β-diketiminato nickel­(I) species [Me3NN]­Ni­(2-picoline) (1) serves as an efficient catalyst for carbodiimide (RNCNR′) formation in the reactions of a range of organoazides N3R with isocyanides R′NC. [Me3NN]­Ni­(CNR)2 (R = tBu, Ar (Ar = 2,6-Me2C6H3)) species provide carbodiimides RNCNAr′ upon reaction with Ar′N3 (Ar′ = 3,5-Me2C6H3). Nitrene transfer takes place via the intermediacy of nickel imides. Reaction of [MexNN]­Ni­(2-picoline) (x = 2 or 3) with Ar′N3 gives the new dinickel imides {[MexNN]­Ni}2(μ-NAr′) (4 (x = 3) and 5 (x = 2)) as deep purple, diamagnetic substances. The X-ray structure of {[Me2NN]­Ni}2(μ-NAr′) (5) features short Ni–Nimide distances of 1.747(2) and 1.755(2) Å along with a short Ni–Ni distance of 2.7210(3) Å. These dinickel imides 4 and 5 react stoichiometrically with tBuNC to provide the corresponding carbodiimides tBuNCNAr′ in good yield. Azide transfer takes place upon reaction of 1 with TMS-N3 to give the square planar nickel­(II) azide [Me3NN]­Ni­(N3)­(2-picoline) (7). Stoichiometric reaction of dinickel dicarbonyl {[Me3NN]­Ni}2(μ-CO)2 with organoazides such as Ar′N3 is sluggish, indicating that 1 is not an efficient catalyst for nitrene transfer from organoazides to CO to form isocyanates RNCO.