Synthesis of Silyl- and Germyl-substituted Borates and their Application to Catalytic Reactions

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Silylborats, (Li[Ph_nMe_<3-n>SiBPh_3], n = 1-3), and germylborates, (Li[Ph_nMe_<3-n>GeBPh_3], n = 1-3) and (E[Et_3GeBPh_3], E = Li, Na, K), were prepared by the reaction of the corresponding silyl- and germylalkali metals with triphenylborane in a hexane/benzene mixed solvent The silyl- and germylborates were fully identified by ^1H, ^<13>C, ^<11>B, and ^7Li NMR spectroscopic methods. Germylborates, Li[Ph_3GeBPh_3] and E[Et_3GeBPh_3] (E = Li and Na), were also determined by X-ray diffraction analyses. The polymeric structure of E[Et_3GeBPh_3] was observed in the solid state and in a hydrocarbon solvent. The alkali metal atoms were located near the center of the benzene ring of triphenylborane and interacted with the neighboring borate molecules by the Li^+-π interaction. The polymeric structure was destroyed by the addition of MeOH, however, E[Et_3GeBPh_3] was coordinated by three MeOH molecules to form the dimeric structure without methanolysis reaction. The primary processes in photochemical reactions of silyl- and germylborates were investigated by chemical trapping experiments and CIDEP method. The cleavage of Ge-B (or Si-B) bonds of germylborates (or silylborates) was most probably considered to occur from their triplet states.