高橋 慎太郎

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.

Three‐coordinated chlorogermylenes of the type [Ph2P(RN)2]GeCl (3: R = tBu; 4: R = Dip = 2,6‐iPr2C6H3), which bear an N,N‐substituted iminophosphonamide ligand, were synthesized. The coordination behavior of 3 and 4 toward rhodium(I) complex was investigated. When 3 was treated with 1/2 of an equivalent of [RhCl(cod)]2 (cod = 1,5‐cyclooctadiene), the corresponding chlorogermylene‐Rh(I) complex 5 was obtained as orange crystals. In contrast, the reaction of 4 with a half equivalent of [RhCl(cod)]2 under a CO atmosphere resulted in the formation of a five‐membered germarhodacycle 7. Compounds 3, 4, 5, and 7 were characterized using NMR spectroscopies and single‐crystal X‐ray diffraction. Complex 5 can be employed as a catalyst for the hydrosilylation and hydroboration reactions of diphenylacetylene, thus demonstrating the utility of germylene ligands comparable to those of NHCs in the major transition metal catalytic processes.