Competition between carbene and pseudo eta(3)-allyl bonding modes in a palladium(II) complex of a functionalized bis(imidazolium) ligand

The reaction of the functionalized bis(imidazolium) salt 1,3-bis(1-methylim idazolium-3-yl)propan-2-one diiodide with palladium(II) acetate gave as the sole product the unexpected complex cis-I2Pd[(CHR)(2)C(O)] (R = 1-methylim idazolium-3-yl). Single-crystal X-ray crystallography and infrared spectros copy revealed a highly puckered palladacyclobutan-3-one ring with an eta (3 )-allylic (eta (3)-oxodimethylenemethane) bonding disposition of Pd(II) to the [C-C(O)-C](2-) fragment. No imidazolin-2-ylidene formation was evident. The neutral complex may be viewed as zwitterionic, with the negatively cha rged ligands at the Pd(II) center balanced by the positive charges on the p endant imidazolium groups.