Unusual hydrogenation of fumarate anion followed by metal-carbon bond formation: Synthesis and characterization of two metallochelates

The treatment of [M(dppf)(H20)21(OTf)2 (dppf =1,1'-bis(diphenylphosphino)ferrocene; M = Pd, Pt) with I equiv of disodiurn fumarate in methanol medium showed an unusual hydrogenation of the ethylenic bond followed by the formation of metallochelates linking M through one of the carboxylates and the P-carbon with respect to COO-. Despite the possibility of formation of a [2 + 2] or [4 + 4] selfassembled macrocycle, the reduction of fumarate to succinate, and in particular the linking through the fi-carbon, is unique since a similar treatment using disodium succinate instead of disodium fumarate yielded an expected metallochelate where both the carboxylates were coordinated to the square-planar metal.