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Synlett 2009(16): 2696-2700  
DOI: 10.1055/s-0029-1217957
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

A Highly Efficient Chiral-Bridged Diphosphine Ligand Modified Cationic Palladium(II) Catalyst System for Asymmetric Alternating Copolymerization of Propene and Carbon Monoxide

Yuming Cuia,b, Lailai Wang*a, Fuk Yee Kwong*c, Man Kin Tsed, Albert S. C. Chanc
a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. of China
e-Mail: wll@lzb.ac.cn;
b Graduate University of Chinese Academy of Sciences, Beijing 100039, P. R. of China
c Open Laboratory of Chirotechnology of the Institute of Molecular Technology for Drug Discovery and Synthesis and Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hong Kong, P. R. of China
e-Mail: bcfyk@inet.polyu.edu.hk;
d Leibniz Institute for Catalysis e.V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
Further Information

Publication History

Received 8 May 2009
Publication Date:
04 September 2009 (online)

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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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8

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.