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.