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Three‐Coordinate Nickel(I) Complexes Stabilised by Six‐, Seven‐ and Eight‐Membered Ring N‐Heterocyclic Carbenes: Synthesis, EPR/DFT Studies and Catalytic Activity
Author(s) -
Page Michael J.,
Lu Wei Y.,
Poulten Rebecca C.,
Carter Emma,
Algarra Andrés G.,
Kariuki Benson M.,
Macgregor Stuart A.,
Mahon Mary F.,
Cavell Kingsley J.,
Murphy Damien M.,
Whittlesey Michael K.
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201202950
Subject(s) - aryl , chemistry , isostructural , electron paramagnetic resonance , ring (chemistry) , nickel , catalysis , crystallography , comproportionation , medicinal chemistry , halide , bromine , stereochemistry , inorganic chemistry , nuclear magnetic resonance , crystal structure , organic chemistry , alkyl , physics , electrode , electrochemistry
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 ).