Three-coordinate nickel(I) complexes stabilised by six-, seven- and eight-membered ring N-heterocyclic carbenes: Synthesis, EPR/DFT studies and catalytic activity

M.J. Page, W.Y. Lu, R.C. Poulten, E. Carter, A.G. Algarra, B.M. Kariuki, S.A. MacGregor, M.F. Mahon, K.J. Cavell, D.M. Murphy, M.K. Whittlesey

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69 Citations (Scopus)

Abstract

Comproportionation of [Ni(cod)] (cod=cyclooctadiene) and [Ni(PPh)X] (X=Br, Cl) in the presence of six-, seven- and eight-membered ring N-aryl-substituted heterocyclic carbenes (NHCs) provides a route to a series of isostructural three-coordinate Ni complexes [Ni(NHC)(PPh)X] (X=Br, Cl; NHC=6-Mes 1, 6-Anis 2, 6-AnisMes 3, 7-o-Tol 4, 8-Mes 5, 8-o-Tol 6, O-8-o-Tol 7). Continuous wave (CW) and pulsed EPR measurements on 1, 4, 5, 6 and 7 reveal that the spin Hamiltonian parameters are particularly sensitive to changes in NHC ring size, N substituents and halide. In combination with DFT calculations, a mixed SOMO of |3dz2〉 and |3dx2-y2〉 character, which was found to be dependent on the complex geometry, was observed and this was compared to the experimental g values obtained from the EPR spectra. A pronounced 31P superhyperfine coupling to the PPh3 group was also identified, consistent with the large spin density on the phosphorus, along with partially resolved bromine couplings. The use of 1, 4, 5 and 6 as pre-catalysts for the Kumada coupling of aryl chlorides and fluorides with ArMgY (Ar=Ph, Mes) showed the highest activity for the smaller ring systems and/or smaller substituents (i.e., 1>4≈6≫5).
Original languageEnglish
Pages (from-to)2158-2167
Number of pages10
JournalChemistry - A European Journal
Volume19
Issue number6
Early online date4 Jan 2013
DOIs
Publication statusPublished - 4 Feb 2013

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