作者:Claudio Bianchini、Hon Man Lee、Giuseppe Mantovani、Andrea Meli、Werner Oberhauser
DOI:10.1039/b108804c
日期:2002.4.2
Pyridinimine-modified Pd(II) complexes of general formulae (N-N′)Pd(Y)2 catalyze the methoxycarbonylation of styrene to give dimethyl phenylsuccinate as the largely major product [N-N′ = py-2-C(R)N(2,6-R′C6H3), R = H, Me; R′ = Me, i-Pr; 6-Mepy-2-C(H)N[2,6-(i-Pr)2C6H3]; py-2-C(H)N(C6H5); Y = acetate, trifluoroacetate]. The influence of various catalytic parameters on the overall conversion of styrene to carbonylated products and on the product selectivity has been studied by systematically varying the type of palladium initiator, the concentrations of organic oxidant (1,4-benzoquinone) and protic acid (p-toluenesulfonic
acid), and the CO pressure. By an appropriate choice of the structure of the pyridinimine ligand and of the reaction parameters, turn-over numbers as high as 96 and selectivities in dimethyl phenylsuccinate as high as 98% were obtained. In particular, the overall conversion of styrene is controlled by the steric properties of the alkyl substituents on the imine aryl group, while the nature of the substituent (H or Me) on the imine carbon influences the selectivity. The addition of 2 equivalents of TsOH to the catalytic mixtures generally increased the styrene conversion but lowered the selectivity in dimethyl phenylsuccinate due to greater production of methyl 3,6-diphenyl-4-oxohexanoate. Further additions of TsOH (up to 6 equivalents) resulted in better selectivities and lower conversions for all precursors.
一般公式为 (N-N′)Pd(Y)2 的吡啶亚胺修饰的 Pd(II)配合物催化苯乙烯甲氧羰基化生成二甲基苯基琥珀酸酯作为主要产物 [N-N′= 吡啶-2-C(R)N(2,6-R′C6H3), R= H, Me; R′= Me, i-Pr; 6-Mepy-2-C(H)N[2,6-(i-Pr)2C6H3]; 吡啶-2-C(H)N(C6H5); Y= 乙酸酯, 三氟乙酸酯]。通过系统改变钯引发剂类型、有机氧化剂(1,4-苯醌)和质子酸(对甲苯磺酸)的浓度以及 CO 压力,研究了各种催化参数对苯乙烯转化成羰基化产物及其产物选择性的影响。通过适当选择吡啶亚胺配体的结构和反应参数,获得了高达 96 的转换数和高达 98%的二甲基苯基琥珀酸酯选择性。特别是苯乙烯的总体转化受亚胺芳基上烷基取代基的立体性质控制,而亚胺碳上的取代基(H 或 Me)的性质影响选择性。向催化混合物中加入 2 当量的 TsOH 通常会增加苯乙烯的转化率,但由于甲基 3,6-二苯基-4-氧代己酸酯的产量增加,降低了二甲基苯基琥珀酸酯的选择性。进一步添加 TsOH(高达 6 当量)使所有前体的选择性更好,转化率更低。