Formation of N-Heterocyclic Complexes of Rhodium and Palladium from a Pincer Silver(I) Carbene Complex

The pincer ligands 2,6-bis( n -butylimidazoliummethyl)pyridine dihalide (halide = Cl ( 3a ), Br ( 3b ) are easily obtained by the reaction of n -butylimidazole with 2,6-bis(chloromethyl)pyridine and 2,6-bis(bromomethyl)pyridine in a 2:1 molar ratio, respectively. Ligand 3a readily reacts with Ag 2 O in CH 2 Cl 2 to yield the bis(silver carbene) complex [2,6-bis( n -butylcarbenemethyl)pyridine][AgCl] 2 ( 4 ) in 70% yield. The reaction of 4 with (PhCn) 2 PDCl 2 in CH 2 Cl 2 yields the palladium carbene complex Pd[2,6-bis( N - n -butylcarbenemethyl)pyridine]Cl 2 ( 5 ). The reaction of equimolar amounts of 4 and [Rh(COD)Cl] 2 (COD = cyclooctadiene) in CH 2 Cl 2 gave the dirhodium(I) complex [2,6-bis( N - n -butylcarbenemethyl)pyridine][Rh(COD)Cl] 2 ( 6 ). All compounds were characterized by 1 H and 13 C NMR spectroscopy. The solid-state structures of 4 and 6 were determined by X-ray crystallography.