Catalytic activity of cationic diphospalladium(II) complexes in the alkene/CO copolymerization in organic solvents and water in dependence on the length of the alkyl chain at the phosphine ligands

A series of diphos ligands CH2(CH2PR2)(2), (1a-x) (a-g: R = (CH2)(n)OH, n = 1, 3-8; h-k: R = (CH2)(n)CH(CH2OH)(2), n = 3-6; 1-u: R = CnH2n+1, n =1-8, 10, 14; v-x: R =CH(CH3)(2), (CH2)(2)CH(CH3)(2), (CH2)(3)CH(CH3)(2), (Scheme 1), provided with functionalities of different polarity, was prepared phot ochemically by hydrophosphination of the corresponding 1-alkenes with H2P(C H2)(3)PH2 or reaction of Grignard reagents with Cl2P(CH2)(3)PCl2. The water -soluble palladium complexes [(R2P(CH2)(3)PR3)Pd(OAc)(2)] (2a-k) were obtai ned by reaction of Pd(OAc)(2) with the ligands 1a-k in ethanol-acetonitrile . Treatment of PdCl2(NCC6H5)(2) with 1l-x afforded the dichloropalladium(II ) complexes [R2P(CH2)(3)PR2)PdCl2] (3l-x). Upon chloride abstraction with A gBF4 in dichloromethane-acetonitrile the dicationic palladium(II) complexes [(R2P(CH2)(3)PR2)Pd(NCCH3)(2)][BF4](2) (4l-x) are formed. The structure of 4n (R = n-Pr) was investigated by an X-ray structural analysis. In particu lar the water-soluble complexes 2c-k proved to be highly active in the carb on monoxide/ethene copolymerization under biphasic conditions (water-toluen e). In the presence of an emulsifier and methanol as activator the catalyti c activity increased by a factor of about three. Also higher olefins could be successfully incorporated into the copolymerization with CO and the terp olymerization with ethene and CO. The catalytic activity of the dicationic complexes 4l-x in the propene or 1-hexene/CO copolymerization strongly depe nds on the length of the alkyl chain R. At 25 degrees C a maximum is achiev ed in the case of 4q (R = nHex) which is five times more active than the co rresponding catalyst with the dppp-ligand. This maximum is shifted to 4t (R = n-C10H21) if the temperature is raised to 60 degrees C. The 1-alkene/CO copolymers are distinguished by their regioregular microstructure and their ultra high molecular weights. Compared to the sulfonated dppp-SO3 catalyst the water-soluble complexes 2c,e,f,h are responsible for a higher 1-hexene incorporation in the terpolymerization of ethene with l-hexene and CO. (C) 2000 Elsevier Science S.A. All rights reserved.