β‑Diketiminato Nickel Imides in Catalytic Nitrene Transfer to Isocyanides

Abstract

The β-diketiminato nickel­(I) species [Me₃NN]­Ni­(2-picoline) (<b>1</b>) 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 [Me_<i>x</i>NN]­Ni­(2-picoline) (<i>x</i> = 2 or 3) with Ar′N₃ gives the new dinickel imides {[Me_<i>x</i>NN]­Ni}₂(μ-NAr′) (<b>4</b> (<i>x</i> = 3) and <b>5</b> (<i>x</i> = 2)) as deep purple, diamagnetic substances. The X-ray structure of {[Me₂NN]­Ni}₂(μ-NAr′) (<b>5</b>) features short Ni–N_imide 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 <b>4</b> and <b>5</b> react stoichiometrically with ^tBuNC to provide the corresponding carbodiimides ^tBuNCNAr′ in good yield. Azide transfer takes place upon reaction of <b>1</b> with TMS-N₃ to give the square planar nickel­(II) azide [Me₃NN]­Ni­(N₃)­(2-picoline) (<b>7</b>). Stoichiometric reaction of dinickel dicarbonyl {[Me₃NN]­Ni}₂(μ-CO)₂ with organoazides such as Ar′N₃ is sluggish, indicating that <b>1</b> is not an efficient catalyst for nitrene transfer from organoazides to CO to form isocyanates RNCO