Bidentate phosphine ligands have been prepared on polystyrene beads modified with polyether dendron spacers. When complexed to Pd0, these systems exhibited a negative dendritic effect on Heck catalysis (contrary to the analogous monodentate phosphine systems), but mostly a positive influence on carbonylation. This opposite influence of the dendronization falls into line with other differences in the optimal ligand structure for the two reactions. The negative effect on the Heck catalysis with bidentate phosphines may indicate that dendrimer-induced reduction in the cross-linking upon Pd complexation is responsible for the positive effect in the corresponding monodentate phosphine systems.
在聚
苯乙烯珠上制备了双齿
膦配体,并用聚醚树枝状间隔物进行了修饰。当与 Pd0 复配时,这些系统对 Heck 催化(与类似的单齿膦系统相反)表现出负面的树枝状效应,但对羰基化却大多表现出正面的影响。树枝化的这种相反影响与这两种反应的最佳
配体结构的其他差异是一致的。双齿膦对 Heck 催化作用的负面影响可能表明,在相应的单齿膦体系中,
钯络合时树枝状聚合物引起的交联减少是产生正面影响的原因。