β-(Z) Selectivity Control by Cyclometalated Rhodium(III)–Triazolylidene Homogeneous and Heterogeneous Terminal Alkyne Hydrosilylation Catalysts

Abstract

The cyclometalated Rh(III)-NHC compounds [Cp*RhI(C,C')-Triaz] (Triaz = 1,4-diphenyl-3methyl-1,2,3-triazol-5-ylidene) and [Cp*RhI(C,C')-Im] (Im = 1-phenyl-3-methyl-imidazol-2ylidene) are efficient catalysts for the hydrosilylation of terminal alkynes with complete regio-and stereoselectivity towards the thermodynamically less stable β-(Z)-vinylsilane isomer at room temperature in chloroform or acetone. Catalyst [Cp*RhI(C,C')-Triaz] shows a superior catalytic performance in terms of activity and has been applied to the hydrosilylation of a range of linear 1alkynes and phenylacetylene derivatives with diverse hydrosilanes, including HSiMePh2, HSiMe2Ph, HSiEt3 and the bulkier heptamethylhydrotrisiloxane (HMTS), to afford the corresponding β-(Z)-vinylsilanes in quantitative yields. The graphene-based hybrid material proposed mechanism entails the Rh-CAr assisted hydrosilane activation to afford a reactive Rhsilyl intermediate that leads to a (E)-silylvinylene intermediate after alkyne insertion and a metallacyclopropene-driven isomerization. The release of the -(Z)-vinylsilane product can occur by a reversible cyclometalation mechanism involving -CAM with the CAr-H bond or,alternatively, the Si-H bond of an external hydrosilane. The energy barrier for the latter is 1.2 kcal•mol -1 lower than that of the CAr-H bond, which results in a small energy span difference that makes both pathways competitive under catalytic conditions.

Recent Advances in the Syntheses and Catalytic Applications of Homonuclear Ru‐, Rh‐, and Ir‐Complexes of CNHC^C Cyclometalated Ligands

“…Chemistry-A European Journal plexes (A and B in scheme 39) can catalyse the hydrosilylation of terminal alkynes effectively with complete regio-and stereoselectivity toward the thermodynamically less stable isomer β-(Z)-vinylsilane at room temperature. [51] Catalyst A with a mesoionic carbene ligand displays better activity and successfully hydrosilylated a range of linear 1alkynes and phenylacetylene derivatives with diverse hydrosilanes (HSiMePh 2 , HSiMe 2 Ph, HSiEt 3 , and the bulkier heptamethylhydrotrisiloxane (HMTS)) to access various β-(Z)-vinylsilanes in near quantitative yields. They have also synthesized the graphene connected Rh III -triazolylidene hybrid material C by covalently immobilizing the cyclometalated complex A through the triazolylidene linker.…”

Rh(I)/(III)‐N‐Heterocyclic Carbene Complexes: Effect of Steric Confinement Upon Immobilization on Regio‐ and Stereoselectivity in the Hydrosilylation of Alkynes

“…In the solid state, the rhodium is coordinated both to the NHC's C 2 carbon and the pyridine nitrogen. It adopts a three‐legged piano‐stool‐type geometry as observed for other half‐sandwich complexes [18a] . Complex Rh9 (Figure 3) crystallizes in the triclinic space group P‐1 with distorted octahedral geometry at the metal centre.…”

Transition-Metal-Catalyzed Stereo- and Regioselective Hydrosilylation of Unsymmetrical Alkynes

“…The β-Z selective hydrosilylation of terminal alkynes were dominated by noble metal catalysts, especially Rh ( 3, entries 9 and 10). [78][79] Both Ir(I) and Ir(III) complexes were prove to be suitable catalysts for β-Z selective hydrosilylation of alkynes (Table 3, entries 11-16). [80][81][82][83][84][85][86] The hard-basic ligands with N, O, C as coordinative groups seems suitable for Ir catalysts.…”

“…The Rh catalysts gave mainly -Z-selectivity in hydrosilylation of terminal alkynes (Table 3, entries 1-10), 43,[45][46][47][48][49][75][76][77][78][79] which was greatly different from Pt catalysts (Table 1, entries 1-14). The Rh(I) and Rh(III) complexes were suitable catalysts for this purpose.…”