Normal and abnormal carbene complexes derived from thiazole: Preparation and a preliminary investigation of their relative catalytic performance
Article in Press
Readily prepared 2-, 4- and 5-bromo-3-methyl thiazolium triflates react by oxidative substitution with M(PPh3)4 (M = Ni or Pd) to furnish five of the expected normal and abnormal cationic thiazolylidene complexes (1a, 1b, 2a, 2b, and 3b). Carbene complex formation is accompanied by a ca. 40 ppm downfield shift of the α-N carbene carbons in Pd complexes 1 and 2 in their 13C NMR spectra but the chemical shift of C(carbene) in the abnormal 3b (δ 135.7) is particularly low. Crystal and molecular structures of complexes 1a, 2b, and 3b all indicate a square planar arrangement of the ligands around the central metal atoms. The new complexes catalyse Suzuki-Miyaura aryl coupling. © 2011 Elsevier Ltd. All rights reserved.