Synthesis of mono- and di-nuclear palladium(II) complexes containing ylide ligands [PPh2(CHCO2R)2]–(R = Me or Et). Crystal structures of [Pd{(CHCO2Et)2PPh2}2], [Pd{(CHCO2Et)2PPh2}Cl(PPh3)], and [Pd{(CHCO2Et)2PPh2}(NC5H5)2]ClO4

Abstract

Complexes [Ag₂{µ-(CHCO₂R)₂PPh₂}₂](R = Me or Et) react (1:1) with trans-[PdCl₂(NCPh)₂] to give spirane complexes [Pd{(CHCO₂R)₂PPh₂}₂][R = Me, (1a); or Et, (1b)] which, in turn, react with PdCl₂(1 : 1) to give [Pd₂{(CHCO₂R)₂PPh₂}₂(µ-Cl)₂][R = Me, (2a); or Et, (2b)]. Complex (1a) can also be obtained by treating (2a) with [Ag₂{µ-(CHCO₂Me)₂PPh₂}₂](1 : 1). Complexes (2a) and (2b) react with neutral ligands to yield [Pd{(CHCO₂R)₂PPh₂}ClL][R = Me, L = pyridine (py), (3a), or PPh₃, (4a); R = Et, L = py, (3b), or PPh₃, (4b)] or with neutral ligands in the presence of NaClO₄to give [Pd{(CHCO₂R)₂PPh₂}L₂]ClO₄[R = Me, L₂= 2,2′-bipyridyl, (5a), or 1,2-bis(diphenyl-phosphino)ethane, (6a); R = Et, L = py, (7b)]. When (2a) is treated with TI(acac)(Hacac = acetylactone) or TI(cp)(cp = cyclopentadienyl)(1 : 2), [Pd{(CHCO₂Me)₂PPh₂}(acac)](8a) or [Pd{(CHCO₂Me)₂PPh₂}(η-cp)](9a) are obtained, respectively. The X-ray structures of complexes (1b)(which displays crystallographic inversion symmetry), (4b), and (7b) have been determined, showing a chelating co-ordination of all ylide ligands, the methine carbon donor atoms of which adopt RR or SS configurations. The chelate rings are non-planar. The Pd–C bond lengths reflect the various trans influences.