β-Diketiminato Nickel Imides in Catalytic Nitrene Transfer to Isocyanides

Abstract

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.