SYNTHESIS OF ETA(2)-PHOSPHONIOALKENE-PALLADIUM(O) COMPLEXES FROM ALKENYLPHOSPHONIUM HALIDES AND PALLADIUM(O) SPECIES - STRUCTURE AND SUBSTITUTION-REACTIONS OF THESE COMPLEXES

Treatment of Pd(dba)(2) (dba = dibenzylideneacetone) with (trans-RCH=C HPPh3)Br-+(-) in dichloromethane afforded [Pd(trans-RCH=CHPPh3)(2)Br]( +) (R = CO2Et (4), CO2Me (5), Ph (6)). As shown by the results of the X-ray diffraction, 4 adopts a distorted pentagonal geometry with two E tO2CCH=CH(PPh3)+ moieties and a bromide ligand. The C-C double bond in the EtO2CCH=CH(PPh3)(+) moieties are pi-bonded to the palladium(0) ce nter and are coplanar with the bromide ligand and the metal center. Bo th (EtO2CCH=CHPPh3)C moieties are oriented with the two PPh3 groups tr ans to each other and the olefin carbon that is attached to PPh3 occup ying the coordination site neighboring to the bromide ligand. Treatmen t of trans-[(RCH)-C-1=CR2(PPh3)]Br-+(-) with Pd(dba)(2) in the presenc e of 1 equiv of PPh3 or P(OPh)(3) gave the corresponding palladium com plexes Pd[trans-(RCH)-C-1=CR2(PPh3)](L)Br (L = PPh3, R-1 = Ph, R-2 = H (3). L = PPh3, R-1 = Me, R-2 = H (7); R-1 = CO2Et, R-2 = H (8); R-1 = CO2Me, R-2 = H (9); R-1 = H, R-2 = Me(10). L = P(OPh)(3), R-1 = CO2Me , R-2 = H (11)) in 54-92% yields. Substitution studies showed complexe s 3 and 9 react with dppe (1,2-bis(diphenylphosphino)ethane) in dichlo romethane to give [Pd(RCH=CH(PPh3)(dppe)]Br-+(-)(R = Ph (12); R = CO2M e (13)), but treatment of 9 and 11 with PPh3 and P(OPh)(3), respective ly, afforded only the original complexes on isolation.