Palladium carbene complexes derived from imidazolium-linked ortho-cyclophanes

Abstract

Reaction of imidazolium-linked ortho-cyclophanes with nickel(II) and palladium(II) salts in the presence of acetate base led to the formation of complexes where a metal centre is bound by a pair of heterocyclic carbenes which themselves are part of a cyclophane skeleton. These cyclophane–metal complexes have been characterised by NMR spectroscopy and (for five complexes) X-ray diffraction studies. The complexes are highly active as promoters of Heck and Suzuki couplings, with preliminary studies showing Heck reactions with turnover numbers approaching 107.