Palladium(II) complexes with hemilabile etherdiphos ligands in the alternating copolymerization of carbon monoxide with olefins

Abstract

The potentially hexadentate diphos ligands (ROCH 2CH 2) 2P(CH 2) 3P(CH 2CH 2OR) 2 ( 1a-d) (R=Et ( a), n-Bu ( b), t-Bu ( c), Cy ( d)) are accessible by photochemically induced hydrophosphination of the vinyl ethers CH 2CHOR with the diprimary phosphine H 2P(CH 2) 3PH 2. Treatment of 1a–d with (PhCN) 2PdCl 2 in CH 2Cl 2 leads to the dichlorodiphospalladium(II) complexes 2a–d, from which the dicationic palladium(II) complexes 3a–d were obtained by abstraction of the chlorides with AgBF 4 in CH 2Cl 2. In 3a–d the etherdiphos ligands are coordinated in a η 4(O,P;O′,P′) fashion. A rapid chemical exchange between the η 2-P ∩O chelated and the η 1-P coordinated part of the ligands in 3a–d was demonstrated by means of temperature-dependent 13C{ 1H} NMR spectroscopy. Both PdO bonds in 3a–d are easily cleaved by polar solvents such as acetonitrile and water resulting in the formation of the adducts 3b · 2CH 3CN, 3c · H 2O, and 3c · 2H 2O. The molecular structures of 2a and 3c · H 2O were determined by single crystal X-ray diffraction methods. Under a total pressure of 60 bar ethene/CO and propene/CO, respectively, 3a-d are highly active catalysts in the copolymerization of olefins with carbon monoxide. GPC measurements revealed high molecular weights of these polyketones.