Palladium Complexes with Bulky Diphosphine Ligands as Highly Selective Catalysts for the Synthesis of (Bio-) Adipic Acid from Pentenoic Acid Mixtures.

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• 作者：Choon Heng Low ; James D. Nobbs ; Martin van Meurs ; Ludger P. Stubbs ; Eite Drent ; Srinivasulu Aitipamula ; Michelle H. L. Pung
• 刊名：Organometallics
• 出版年：2015
• 出版时间：September 14, 2015
• 年：2015
• 卷：34
• 期：17
• 页码：4281-4292
• 全文大小：458K
• ISSN：1520-6041

文摘

A series of sterically bulky diphosphines have been prepared, including P₂ = trans-1,2-bis[(di-tert-butylphosphino)methyl]cyclohexane (4), (2-methylenepropane-1,3-diyl)bis(di-tert-butylphosphine) (5), bis[(di-tert-butylphosphino)methyl]dimethylsilane (6), and cis- and trans-11,12-bis[(di-tert-butylphosphino)methyl]-9,10-dihydro-9,10-ethanoanthracene (10 and 11). The corresponding palladium complexes of these ligands, P₂Pd(CF₃CO₂)₂, have been synthesized and characterized. The solid-state structures of [Pd(4)(CF₃CO₂)₂], [Pd(5)(CF₃CO₂)₂], [Pd(6)(CF₃CO₂)₂], and [Pd(11)(CF₃CO₂)₂] were obtained by single-crystal X-ray diffraction and confirm the bidentate binding mode of the ligand and a square-planar coordination geometry with a minor distortion from the ideal. The diphosphines in combination with Pd(OAc)₂ have been applied in the hydroxycarbonylation of a mixture of pentenoic acid isomers to produce adipic acid with high selectivity (in several cases >95%). The (regio)selectivity of the hydroxycarbonylation reaction is highly dependent on the P₂ diphosphine ligand structure, particularly the steric bulk of the substituents on the diphosphine donor and the P鈥揚d鈥揚 bite angle in the complexes, with respectively tertiary alkyl phosphine substituents (tert-butyl, adamantyl) and a C4 backbone P鈥揚d鈥揚 bite angle >100掳 being the common features of highly adipic acid selective systems. It is suggested that the regioselectivity of hydroxycarbonylation becomes largely driven by the chelation of the carboxylic acid functionality of pentenoic acid substrates, when smaller size P substituents and/or when P₂ ligands with smaller bite angles (<100掳) are applied.