title: Three-coordinate nickel(I) complexes stabilised by six-, seven- and eight-membered ring n-heterocyclic carbenes: synthesis, EPR/DFT studies and catalytic activity.
abstract: Comproportionation of [Ni(cod)(2)] (cod = cyclooctadiene) and [Ni(PPh(3))(2)X(2)] (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(I) complexes [Ni(NHC)(PPh(3))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 ∣3d z 2〉 and ∣3d x 2-y 2〉 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 (31)P superhyperfine coupling to the PPh(3) 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).
authors.affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Page
authors.forename: Wei Y
authors.initials: WY
authors.lastname: Lu
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Poulten
authors.forename: Emma
authors.initials: E
authors.lastname: Carter
authors.forename: Andrés G
authors.initials: AG
authors.lastname: Algarra
authors.forename: Benson M
authors.initials: BM
authors.lastname: Kariuki
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Macgregor
authors.forename: Mary F
authors.initials: MF
authors.lastname: Mahon
authors.forename: Kingsley J
authors.initials: KJ
authors.lastname: Cavell
authors.forename: Damien M
authors.initials: DM
authors.lastname: Murphy
authors.forename: Michael K
authors.initials: MK
authors.lastname: Whittlesey