Issue 2, 2011

Synthesis and carbene-transfer reactivity of dimeric nickel carbene cations supported by N-heterocyclic carbene ligands

Abstract

Dimeric nickel bridging-carbene complex salts [{(IPr)Ni}2(μ-Cl)(μ-CR1R2)][B(ArF)4](6, R1 = R2 = Ph; 7, R1 = H, R2 = SiMe3) are synthesized by reaction of {(IPr)Ni(μ-Cl)}2 (3) with NaB(ArF)4 and N2CPh2 or N2CHSiMe3, with elimination of N2 and NaCl. The solid-state structure of 6 features an unsymmetric μ,η3-bonding motif for the bridging diphenylcarbene ligand in which one Ni center binds to the CPh2 ligand in a π-fashion involving the ipso- and one ortho-carbon of a phenyl ring along with the carbene carbon. The solution structure (NMR) of 6 indicates a C2v-symmetric structure even at −80 °C. The solid-state structure of 7 shows a (trimethylsilyl)carbene unit symmetrically disposed between the two nickel centers and bound through only the carbene-carbon atom. Diphenylcarbene-group transfer from 6 to carbon monoxide (3 equiv) gives O[double bond, length as m-dash]C[double bond, length as m-dash]CPh2 and the dimeric Ni(I)-Ni(I) carbonyl complex [{(IPr)Ni(CO)}2(μ-Cl)][B(ArF)4] (8). Excess pivaloisocyanide reacts with 6 to afford tBuN[double bond, length as m-dash]C[double bond, length as m-dash]CPh2, [(IPr)Ni(CNtBu)3][B(ArF)4] (9), and (IPr)NiCl(CNtBu) (10). Mesitylazide reacts with 6 to give the ketimine MesN[double bond, length as m-dash]CPh2 and the bridging mesitylimido dimer [{(IPr)Ni}2(μ-Cl)(μ-NMes)][B(ArF)4] (5). A secondary reaction of diphenyldiazomethane with 6 to give Ph2C[double bond, length as m-dash]CPh2 and Ph2C[double bond, length as m-dash]N–N[double bond, length as m-dash]CPh2 prevents catalytic CPh2-group transfer reactions from being realized in these systems.

Graphical abstract: Synthesis and carbene-transfer reactivity of dimeric nickel carbene cations supported by N-heterocyclic carbene ligands

Supplementary files

Article information

Article type
Edge Article
Submitted
31 Aug 2010
Accepted
11 Oct 2010
First published
03 Nov 2010

Chem. Sci., 2011,2, 321-325

Synthesis and carbene-transfer reactivity of dimeric nickel carbene cations supported by N-heterocyclic carbene ligands

C. A. Laskowski and G. L. Hillhouse, Chem. Sci., 2011, 2, 321 DOI: 10.1039/C0SC00464B

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