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DOI: 10.1055/s-0029-1217957
A Highly Efficient Chiral-Bridged Diphosphine Ligand Modified Cationic Palladium(II) Catalyst System for Asymmetric Alternating Copolymerization of Propene and Carbon Monoxide
Publikationsverlauf
Publikationsdatum:
04. September 2009 (online)

Abstract
A highly efficient chiral-bridged biphenyl diphosphine ligand [(R ax)-BuP] modified cationic palladium(II) catalyst system for the synthesis of optically active polyketone by stereoselective alternating copolymerization of propene and carbon monoxide is reported for the first time. The results show that [Pd(MeCN)4][OTf]2 is an excellent catalyst precursor in a mixed solvent of MeNO2-MeOH. The highest catalytic activity was found to be 221 g polymer/(g Pd˙h). A chiral polyketone with molecular weight Mn = 2.9 × 104, polydispersity = 1.4, and molar optical rotation = +37˚ was afforded under optimized reaction conditions.
Key words
palladium - chiral-bridged biphenyl diphosphine - propene and CO - asymmetric alternating copolymerization - chiral polyketone
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References and Notes
General Procedure for the Copolymerization of Propene and Carbon Monoxide: A mixture of Pd(MeCN)4][OTf]2 (0.01 mmol), chiral-bridged ligand (R ax)-BuP (0.012 mmol), and BF3×OEt2 (0.04 mmol) in MeNO2-MeOH (12.5 mL/1 mL) was stirred magnetically under nitrogen for 1 h at r.t. A 100-mL stainless steel reactor was dried, purged with N2, the above catalyst solution was introduced into it, and then propylene (15 g) was introduced first at 0 ˚C followed by carbon monoxide (3.5 MPa). The reaction mixture was heated to 55 ˚C in an oil bath and stirred for 17 h. At the end of a copolymerization the unreacted monomers were vented off after cooling to r.t., and the copolymer was purified by flash column chromatography eluting with CH2Cl2 and acetone consecutively and dried under vacuum at 40 ˚C overnight, resulting in a light yellow solid (3.24 g). ¹³C NMR (125 MHz, CDCl3): δ = 215.6, 212.4, 209.1 (C=O), 44.8 (CH2), 40.1 (CH), 16.5 (Me). ¹H NMR (400 MHz, CDCl3): δ = 2.95-3.06 (CH2), 2.50 (CH), 1.06 (Me). IR (KBr): 1707 (C=O, carbonyl), 825, 1041-1084 (C-O-C, spiroketal). Molar optical rotation: [Φ]D ²0 = +37˚ (c = 5 mg/mL, CHCl3). Number average molecular weight: 2.9 ↔104 versus polystyrene standards, Mw/Mn = 1.4.