Issue 1, 2013

Single-electron oxidation of N-heterocyclic carbene-supported nickel amides yielding benzylic C–H activation

Abstract

The dimeric Ni(I)–Ni(I) N-heterocyclic carbene complex {(IPr)Ni(μ-Cl)}2 (3; IPr = 1,3-(2,6-iPr2C6H3)2imidazolin-2-ylidene)) reacts with the lithium terphenylamides LiNHdmp and LiNHdippp (dmp = 2,6-di(mesityl)phenyl; dippp = 2,6-bis(2,6-di-iso-propylphenyl)phenyl) to give the monomeric Ni(I) amides (IPr)Ni(NHdmp) (4) and (IPr)Ni(NHdippp) (5), respectively. These nickel amides are 1-electron paramagnets, and crystallographic characterization indicates both are stabilized by Ni–C(ipso) interactions with a flanking aryl group of the terphenyl fragment. This results in significant deviation from the linear CNHC–Ni–N geometry typical for a two-coordinate transition-metal complex (112.17(9)° in 4, 116.41(9)° in 5). One-electron oxidation of 4 by ferrocenium results in intramolecular deprotonation at a terphenyl benzylic position by the amide, giving the diamagnetic Ni(II) complex [(IPr)Ni(κ2-C,N:NH2C6H3(Mes)C10H9)][B(ArF)4] (7). DFT calculations on oxidized 4 (i.e., 4+) indicate short amide N⋯CH3 interactions. One-electron oxidation of 5 by ferrocenium gives a new high-spin Ni(II) amide complex salt, [(IPr)Ni(NHdippp)][B(ArF)4] (9). The solid-state structure of 9 indicates it maintains the bent CNHC–Ni–N core. Unlike three-coordinate cationic Ni(II) amides, 9 has not been observed to undergo smooth deprotonation (at N) to afford a two-coordinate imido complex.

Graphical abstract: Single-electron oxidation of N-heterocyclic carbene-supported nickel amides yielding benzylic C–H activation

Supplementary files

Article information

Article type
Edge Article
Submitted
24 Aug 2012
Accepted
19 Sep 2012
First published
24 Sep 2012

Chem. Sci., 2013,4, 170-174

Single-electron oxidation of N-heterocyclic carbene-supported nickel amides yielding benzylic C–H activation

C. A. Laskowski, G. R. Morello, C. T. Saouma, T. R. Cundari and G. L. Hillhouse, Chem. Sci., 2013, 4, 170 DOI: 10.1039/C2SC21345A

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