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)nOH, n=1, 3–8; h–k: R=(CH2)nCH(CH2OH)2, n=3–6; l–u: R=CnH2n+1, n=1–8, 10, 14; v–x: R=CH(CH3)2, (CH2)2CH(CH3)2, (CH2)3CH(CH3)2, ( Scheme 1), provided with functionalities of different polarity, was prepared photochemically by hydrophosphination of the corresponding 1-alkenes with H2P(CH2)3PH2 or reaction of Grignard reagents with Cl2P(CH2)3PCl2. The water-soluble palladium complexes [(R2P(CH2)3PR2)Pd(OAc)2] (2a–k) were obtained 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)3PR2)PdCl2] (3l–x). Upon chloride abstraction with AgBF4 in dichloromethane–acetonitrile the dicationic palladium(II) complexes [(R2P(CH2)3PR2)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 particular the water-soluble complexes 2c–k proved to be highly active in the carbon monoxide/ethene copolymerization under biphasic conditions (water–toluene). In the presence of an emulsifier and methanol as activator the catalytic activity increased by a factor of about three. Also higher olefins could be successfully incorporated into the copolymerization with CO and the terpolymerization with ethene and CO. The catalytic activity of the dicationic complexes 4l–x in the propene or 1-hexene/CO copolymerization strongly depends on the length of the alkyl chain R. At 25°C a maximum is achieved in the case of 4q (R=nHex) which is five times more active than the corresponding catalyst with the dppp-ligand. This maximum is shifted to 4t (R=n-C10H21) if the temperature is raised to 60°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 1-hexene and CO.