Palladium complexes with bridged and unbridged benzimidazolin-2-ylidene ligands

Two equivalents of N,N'-dimethylbenzimidazolyl iodide (1) react with Pd(OAc )(2) to yield the complex cis-bis(N,N'-dimethylbenzimidazoli-2-ylidene)diio do palladium (2). The potentially bidentate ligand 1,1'-methylene-bis(N-met hylbenzimidazolyl) diiodide (3) reacts with Pd(OAc)(2) to yield the complex [1,1-methylene-bis(N-methylbenzimidazolin-2-ylidene)]diiodo palladium (4) with a bidentate carbene ligand. Both complexes were characterised by H-1- and C-13-NMR spectroscopy. The X-ray crystal structures of 2 and 4 reveal t hat methylene-bridging of the benzimidazolin-2-ylidene ligands leads to pal ladium complexes with a reduced C-carbene-Pd-C-carbene angle (91.3(2) in 2 vs. 83.7(3)degrees in 4). In addition, the angles between the planes of the carbene ligands and the PdC2I2 plane are reduced from almost perpendicular in 2 (83.06(10) and 79.84(13)degrees) to 54.4(2) and 51.8(2)degrees in 4, while comparable bond distances in 2 and 4 are identical within experimenta l error. (C) 1999 Elsevier Science S.A. All rights reserved.