高橋 慎太郎

We designed and synthesized a series of three‐coordinated stannylenes featuring an amino‐linked NHC ligand, specifically tailored for the hydroboration of carbonyl compounds and imines. To fine‐tune the catalytic performance both sterically and electronically, various substituents (chloro, triflate, and bis(trimethylsilyl)amino groups) were introduced at the tin center, generating structurally diverse stannylenes. The hydroboration of carbonyl compounds catalyzed by these stannylenes proceeded under mild reaction conditions, affording the corresponding boryl esters in excellent yields with high chemoselectivity. Notably, bis(trimethylsilyl)aminostannylene exhibited outstanding catalytic efficiency, enabling hydroboration with a minimal catalyst loading of 0.01 mol% for aldehydes and 0.1 mol% for ketones, and was tolerant of a wide range of substrates, including sterically hindered and electronically diverse carbonyl compounds. Furthermore, in the hydroboration of imines, the reaction proceeded efficiently with just 5 mol% catalyst, furnishing the corresponding borylamines in high yields. Based on stoichiometric experiments, we propose a plausible catalytic cycle for stannylene‐mediated hydroboration.

An isolable monomeric alumylene stabilized by two donating ligands (phosphine and NHC) has been synthesized. Experimental and theoretical analysis confirms that the NHC ligand in the Al(I)‐complex is labile and reversibly dissociates from the AlI center above ‐20 °C. Of particular interest, despite being thermodynamically stabilized by the two ligands, alumylene complex exhibits a high reactivity with a considerably higher nucleophilicity compared to the mono‐ligated complex. It is interesting to note that the Al(I)‐complex reacts immediately with N2O at ‐90 °C, allowing the synthesis of bisligated aluminum oxide, which is stable up to ‐70 °C.

We report an original reactivity of base‐stabilized C‐phosphonio‐silyne with N2O allowing the synthesis of a base‐stabilized diazosilenyl cation. This silicon analogue of diazoalkenes exhibits a remarkable stability thanks to ligand coordination. In addition, a particular stabilizing effect of the silicon atom of diazoalkene moiety was predicted by DFT calculations.

The hydrosilylation reactions of dihydrosilylium ion, stabilized by coordination of a σ‐donating Ni(0) fragment, has been investigated. This complex with two reactive sites, dihydrosilylium and Ni(0) centers, readily reacts with diphenylacetylene via a selective mono‐hydrosilylation reaction to afford the corresponding Ni(0)‐stabilized (hydro)(vinyl)silylium ion. In the case of ethylene, three equivalents of olefin are consumed to give a cationic Ni(II)‐complex featuring a Bu‐Si+‐NiII‐Et moiety with a NHC‐supported Si atom. DFT calculations indicate that the hydrosilylation proceeds by a classical (Chalk‐Harrod type) mechanism with the assistance of NHC ligand moving between Si and Ni centers according to their stabilization requirements.

Abstract A silyliumylidene ion 2 stabilized by two σ‐donating Ni(0)‐ and Pd(0)‐fragments was successfully synthesized. Due to the σ‐donation of M→Si interactions, 2 presents a pyramidalized cationic silicon center with a localized lone pair. The additional coordination of basic Pd(0) fragment to the mono‐Ni(0)‐stabilized silyliumylidene 1 results in a higher HOMO level and an unchanged HOMO‐LUMO gap and thus, 2 remains highly reactive. Interestingly, the coordination mode at the Si center is closely related to the nature of M‐ligands. Indeed, the donor/donor‐stabilized silyliumylidene ion 2 has been transformed into a donor/acceptor‐stabilized ion 13, featuring a trigonal planar Si center with a vacant orbital, just via a ligand exchange reaction from PCy₃/NHC toward PMe₃.