Novel P,Si-hybrid ligands and their stereoelectronic effect on Rh-catalyzed hydroaminomethylation of olefins

Synthesis of silyl-containing phosphines. • Hydrosilyl-containing phosphines as hydrido-source for formation of rhodium-hydride intermediate. • Hydroaminomethylation with hydrosilyl-containing phosphine ( L2 ) modified Rh-catalyst. Herein a series of silyl-containing P,Si-hybrid ligands ( L2-L6 ) were synthesized, in which L2 was first obtained via the combination of a bulky hydrosilyl-group (Ph 2 HSi-) and a bulky ( t -Bu) 2 P-fragment. The as-synthesized L2-L6 were fully characterized by 31 P/ 1 H/ 13 C NMR and the single-crystal X-ray diffraction to verify the presence of the expected Si-H moiety and their influence on the adjacent phosphine fragment. It was indicated that the incorporated hydrosilyl-group in L2 not only effectively adjusts the electronic and steric effects on the adjacent phosphino-groups but also could directly serve as a hydrido-source to promote the formation of the Rh-H (rhodium-hydride) active intermediate, thereby allowing an efficient Rh-catalyzed hydroaminomethylation of olefins. The 1 H NMR characterization proved that the presence of Si-H moieties in L2 enables the formation of stable Rh-H active species even at room temperature. This efficient generation of metal hydride greatly facilitates the first-step hydroformylation and the second-step condensation, thereby promoting the overall hydroaminomethylation sequence. Download: Download high-res image (208KB) Download: Download full-size image