Synthesis of mono- and di-nuclear palladium( II ) complexes containing ylide ligands [PPh 2 (CHCO 2 R) 2 ] – (R = Me or Et). Crystal structures of [Pd{(CHCO 2 Et) 2 PPh 2 } 2 ], [Pd{(CHCO 2 Et) 2 PPh 2 }Cl(PPh 3 )], and [Pd{(CHCO 2 Et) 2 PPh 2 }(NC 5 H 5 ) 2 ]ClO 4

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.