Electronic effects in the nickel-catalysed hydrocyanation of styrene applying chelating phosphorus ligands with large bite angles ‡
作者:Wolfgang Goertz、Wilhelm Keim、Dieter Vogt、Ulli Englert、Maarten D. K. Boele、Lars A. van der Veen、Paul C. J. Kamer、Piet W. N. M. van Leeuwen
DOI:10.1039/a802269k
日期:——
Chelating phosphorus ligands with a rigid backbone and a large natural bite angle were applied in the nickel-catalysed hydrocyanation of styrene. The para substituents in the diphenylphosphanyl moiety of the 4,6-bis(diphenylphosphanyl)-2,8-dimethylphenoxathiine (Thixantphos) ligands were varied and their electronic effects on the activity and selectivity of the catalytic experiments were investigated. The activity of the nickel complexes decreased when electron-donating substituents lead to a more basic phosphorus while electron-withdrawing substituents led to a higher activity. The results of variable temperature 31P-1H} NMR experiments on the in situ catalysts are discussed in relationship to the catalytic performance. 4,6-Bis(diphenylphosphanyl)-2,8-dimethylphenoxathiine (Thixantphos) L1d and the complexes [NiCl2L1d] 1 and [Ni(CN)2L1a] 2 (p-Me2N on phenyl) have been characterised by single-crystal X-ray diffraction. Complex 2 represents the first crystal structure of a monomeric dicyanonickel(II) complex with a PâP chelating ligand. The geometries of ligand L1d and complex 1 were predicted by molecular mechanics calculations.
采用刚性主链和大自然咬合角的螯合磷配体,在镍催化的苯乙烯氢氰化反应中应用。研究了4,6-双(二苯基膦)-2,8-二甲基苯氧噻啉(Thixantphos)配体中二苯基膦基团的对位取代基的变化及其对催化实验活性和选择性的电子效应。当电子给体取代基使磷的碱性增强时,镍配合物的活性下降;而电子吸收取代基则导致活性提高。讨论了在原位催化剂上进行的可变温度31P-1H} NMR实验的结果与催化性能之间的关系。4,6-双(二苯基膦)-2,8-二甲基苯氧噻啉(Thixantphos)L1d及其配合物[NiCl2L1d] 1和[Ni(CN)2L1a] 2(苯基上的p-Me2N)通过单晶X射线衍射进行了表征。配合物2代表了第一个具有P–P螯合配体的单体二氰镍(II)配合物的晶体结构。通过分子力学计算预测了配体L1d和配合物1的几何构型。