The First Carbodiphosphorane Complex with Two Palladium Centers Attached to the CDP Carbon: Assembly of a Single-Stranded di-Pd Helicate by the PCP Pincer ligand C(dppm)2

Abstract

The reaction of the protonated PCP pincer carbodiphosphorane (CDP) complex [PdCl(CH(dppm)2)]Cl2 (1) with [PdCl2(MeCN)2] results in the opening of one ring of the pincer structure and affords the betaine [Pd2Cl5(CH(dppm)2)] (2). The [CH(dppm)2]+ ligand forms a five-membered chelate ring with the Pd(1)Cl2 moiety via the protonated CDP carbon (positively charged) and one phosphine functionality and bridges to the anionic Pd(2)Cl3 fragment via the second phosphine phosphorus. The complex is chiral due to a stereocenter at the protonated CDP carbon atom. Treatment of 2 with water effects deprotonation of the CDP carbon, C–H activation at one methylene group, and the coordination of the second Pd to the CDP carbon. The resulting tricyclic complex [Pd2Cl3(C(dppm)(Ph2CHPh2))] (3) is the first compound with two Pd centers coordinated to a CDP carbon. Compound 3 forms a single-stranded helicate structure and exhibits two interdependent carbon stereocenters, resulting in only two possible enantiomers. The complexes 2·2CH2Cl2 and 3·3CH2Cl2 crystallize in the chiral space group P21, whereby a spontaneous resolution of the enantiomers occurs in both cases.