SYNTHESIS OF A TRIPALLADIUM CLUSTER CONTAINING AN ETA(1)ETA(2)ETA(2)-BRIDGING BUTADIENYL LIGAND STABILIZED BY A ZWITTERIONIC STRUCTURE

An eta(1)-butadienyl complex [{trans-eta(1)-CH2=C(Me)C=CH2}Pd(PPh3)(2) Cl] (1) reacted with u-eta(2):eta(2)-1,3-butadiene)Pd-2(PPh3)(mu-Cl)Cl ] (2) to result in displacement of the diene ligand of 2 accompanied b y exchange of PPh3 of 1 with Cl anion of 2 producing a butadienyl trip alladium cluster 2=C(Me)C=CH2)Pd(PPh3)Cl-2}.{Pd-2(PPh3)(2)(mu-Cl)}] (3 ) stabilized by the zwitterionic structure in moderate yield. The X-ra y structure analysis of 3 revealed rigid binding of [Pd-3(PPh3)(2)(mu- Cl)](+) and[{CH2=C(Me)C=CH2}Pd(PPh3)Cl-2](-) through the pi-bond coord ination of the butadienyl group to the dipalladium cation.