Late-Stage Generation of Bidentate η3-Benzophosphorine–Phosphino Ligands from a Rhodium PCcarbeneP Pincer Complex and Their Use in the Catalytic Hydrosilylation of Alkynes

Dirhodium(II)/XantPhos Catalyzed Synthesis of β-(E)-Vinylsilanes via Hydrosilylation and Isomerization from Alkynes

A concise hydrosilylation of alkynes for synthesizing β-(E)-vinylsilanes catalyzed by dirhodium(II)/XantPhos has been developed. In this reaction, β-(E)-vinylsilanes were generated from the isomerization of β-(Z)-vinylsilanes catalyzed by dirhodium(II) hydride species rather than the direct insertion of triple bond into M-H or M-Si bond (traditional Chalk-Harrod mechanism or modified Chalk-Harrod mechanism). The hydrosilylation displayed a broad substrate scope for alkynes and tertiary silanes, tolerating diverse functional groups including halides, nitriles, amines, esters, and heterocycles.

Synthesis of α-Vinyltrialkoxysilanes via Nickel-Mediated Cross-Electrophile Coupling Reactions

Vinyltrialkoxysilanes are indispensable for organic synthesis, particularly cross-coupling reactions. Hydrosilylation of alkynes inevitably yields α- and β-isomers of vinyltrialkoxysilanes even with complex ligands and catalysts, limiting its usage in organic synthesis. We report the synthesis of α-vinyltrialkoxysilanes via cross-electrophile C(sp2)-C(sp2) coupling of bromoalkenes. The method is quite compatible with functional groups under milder reaction conditions. The gram-scale synthesis of most substrates is impressive. The intermediacy of vinyl iodide and radical escape rebound path are supported by mechanistic studies.

Tuning Ruthenium Carbene Complexes for Selective P-H Activation through Metal-Ligand Cooperation

The use of iminophosphoryl-tethered ruthenium carbene complexes to activate secondary phosphine P-H bonds is reported. Complexes of type [(p-cymene)-RuC(SO2 Ph)(PPh2 NR)] (with R = SiMe3 or 4-C6 H4 -NO2 ) were found to exhibit different reactivities depending on the electronics of the applied phosphine and the substituent at the iminophosphoryl moiety. Hence, the electron-rich silyl-substituted complex undergoes cyclometallation or shift of the imine moiety after cooperative activation of the P-H bond across the M=C linkage, depending on the electronics of the applied phosphine. Deuteration experiments and computational studies proved that cyclometallation is initiated by the activation process at the M=C bond and triggered by the high electron density at the metal in the phosphido intermediates. Consistently, replacement of the trimethylsilyl (TMS) group by the electron-withdrawing 4-nitrophenyl substituent allowed the selective cooperative P-H activation to form stable activation products.

Access to and Reactivity of Fe0 , Fe-I , FeI , and FeII PCcarbene P Pincer Complexes

Despite their promising metal-ligand cooperative reactivity, PC_carbene P pincer ligands are rarely reported for first-row transition-metal centres. Using a dehydration methodology, we report access to an Fe⁰ PC_carbene P pincer complex (1) that proceeds via an isolated α-hydroxylalkyl hydrido complex (3). Reversible carbonyl migration to the carbene position in 1 is found to allow coordination chemistry and E-H bond addition (E=H, B, Cl) across the iron-carbene linkage, representing a unique mechanism for metal-ligand cooperativity. The PC_carbene P pincer ligand is also found to stabilize formal Fe^II , Fe^I , and Fe^-I oxidation states, as demonstrated with synthesis and characterization of the complexes [11-X][BAr^F ₂₀ ] (X=Br, I), 12, and K[13]. Compound K[13] is found to be highly reactive, and abstracts hydrogen from a range of aliphatic C-H sources. Computational analysis by DFT suggests that the formal Fe^I and Fe^-I complexes contain significant carbene radical character. The ability of the PC_carbene P ligand scaffold to partake in metal-ligand cooperativity and to support a range of iron oxidation states renders it as potentially useful in many catalytic applications.