Insertion of an overcrowded silylene into hydro- and haloboranes: A novel synthesis of silylborane derivatives and their properties

Article abstract of DOI:10.1021/om049558w

Reactions of stable silylene-isocyanide complexes Tbt(Mes)SiCNAr (3a, Ar = Mes*; 3b, Ar = Tbt; 3c, Ar = Tip; Tbt = 2,4,6-tris[bis(trimethylsilyl) methyl]phenyl, Mes = mesityl, Mes* = 2,4,6-tri-tert-butylphenyl, Tip = 2,4,6-triisopropylphenyl) with boron compounds were investigated. Reactions of 3a,b with BH₃·THF afforded the first stable silylborane-isocyanide complexes, Tbt(Mes)SiHBH₂·CNAr (4a,b). Silylene complex 3a reacted with BH₃·PPh₃ as well to give the corresponding silylborane-phosphine complex Tbt(Mes)SiHBH ₂·PPh₃ (12). In addition, silylene 2 thermally generated from the corresponding disilene, Tbt(Mes)Si= Si(Mes)Tbt (1), gave 12 when reacted with BH₃·PPh₃. These results strongly suggested that the reactions of 3 with BH₃·THF and BH ₃·PPh₃ proceeded via insertion of a silylene, Tbt-(Mes)Si: (2), into the B-H bond rather than the nucleophilic attack of the silicon atom of 3 toward the boron atom. Thermal dissociation of 4 and 12 into a base-free silylborane, Tbt(Mes)SiHBH₂ (9), was evidenced by the base-exchange reactions. Furthermore, silylene 2 was found to insert into boron-halogen bonds as well as boron-hydrogen bonds. The novel reactivity of silylene 2 was applied to the syntheses of a variety of silylborane derivatives such as base-free silylboranes, silylborane-isocyanide complexes, and silylborates.