Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
Faraday Discuss. 2019 Jul 4;215(0):123-140. doi: 10.1039/c8fd00164b.
To explore the influence of a biologically inspired second and outer coordination sphere on Rh-bis(diphosphine) CO2 hydrogenation catalysts, a series of five complexes were prepared by varying the substituents on the pendant amine in the P(Et)2CH2NRCH2P(Et)2 ligands (PEtNRPEt), where R consists of methyl ester modified amino acids, including three neutral (glycine methyl ester (GlyOMe), leucine methyl ester (LeuOMe), and phenylalanine methyl ester (PheOMe)), one acidic (aspartic acid dimethyl ester (AspOMe)) and one basic (histidine methyl ester (MeHisOMe)) amino acid esters. The turnover frequencies (TOFs) for CO2 hydrogenation for each of these complexes were compared to those of the non-amino acid containing [Rh(depp)2]+ (depp) and [Rh(PEtNMePEt)2]+ (NMe) complexes. Each complex is catalytically active for CO2 hydrogenation to formate under mild conditions in THF. Catalytic activity spanned a factor of four, with the most active species being the NMe catalyst, while the slowest were the GlyOMe and the AspOMe complexes. When compared to a similar set of catalysts with phenyl-substituted phosphorous groups, a clear contribution of the outer coordination sphere is seen for this family of CO2 hydrogenation catalysts.
为了探究受生物启发的第二配体和外部配位层对 Rh-双二膦 CO2 氢化催化剂的影响，我们通过改变 P(Et)2CH2NRCH2P(Et)2 配体（PEtNRPEt）中侧链伯胺上取代基的方式，制备了一系列 5 种配合物。其中，R 由甲酯修饰的氨基酸组成，包括三种中性（甘氨酸甲酯（GlyOMe）、亮氨酸甲酯（LeuOMe）和苯丙氨酸甲酯（PheOMe））、一种酸性（天冬氨酸二甲酯（AspOMe））和一种碱性（组氨酸甲酯（MeHisOMe））氨基酸酯。我们比较了这些配合物中每一种在 CO2 氢化反应中的转化频率（TOF），并与不含氨基酸的 [Rh(depp)2]+（depp）和 [Rh(PEtNMePEt)2]+（NMe）配合物进行了比较。每个配合物都能在温和条件下在四氢呋喃中催化 CO2 氢化生成甲酸盐。催化活性跨度为四倍，最活跃的物种是 NMe 催化剂，而最慢的是 GlyOMe 和 AspOMe 配合物。与一组具有苯基取代膦基团的类似催化剂相比，这种 CO2 氢化催化剂家族明显受到外部配位层的影响。
