The Effect of Weakly Coordinating Solvent and Counter Anion on Diphosphine‐Palladium(II) Catalytic Reactivity for Copolymerization of 1‐Butene with Carbon Monoxide in Aqueous Media

Abstract

AbstractWater soluble bis(acetonitrile) diphospalladium (II) complexes cis‐[Pd(L1–L5)(NCCH3)2][BF4]2 (C1–C5) were obtained by the reaction [Pd(NCCH3)4][BF4]2 with diphosphines ligands L1–L5 (CH2(CH2PR2)2: where R=(CH2)nP(O)(OEt)2, n=2–4, n=6 and n=8)) in dichloromethane–acetonitrile. The isolated complexes were characterized by elemental analysis, FTIR, 1H‐ and 31P‐NMR spectroscopy. The complexes were applied as catalysts for the copolymerization of 1‐butene with carbon monoxide in aqueous media. The present work emphasized on the effect of weakly coordinated solvent and counterion on the catalytic behavior of cis‐[Pd(L1–L5)(NCCH3)2][BF4]2 complexes compared to previously prepared cis‐[ Pd(L1–L5)(OAc)2] (A1–A5). The exchange of π‐bonding NCCH3 ligand with π‐bonding CO and alkene was more favored than the exchange of σ‐bonding OAc− as reflected by the much higher catalytic activity (TON) of the former compared to the latter. In order to compare the catalytic efficiency of water soluble complexes with the performance of a standard, the water insoluble complex, cis‐[Pd(CH2(CH2P(CH2CH3)2)2(NCCH3)2][BF4]2, C6, was prepared and incorporated in the investigations. The isolated alternating 1‐butene/CO copolymer exhibits glass transition temperature of Tg=−3–−15 °C, which is in the range desirable for latex emulsion application. The solid content is up to 21 % with high molecular weight (Mw=4×104 g mol−1) and narrow polydispersities (Mw/Mn=2–3). The C5 complex was found to be fourteen times more active in aqueous polymerization medium (6369 mol substr. mol Pd−1 h−1) than C6 complex in nonaqueous medium (441 mol substr. mol Pd−1 h−1).