Preparation, Structural Characterization, and Photochemical Reactions of Silyl- and Germylborates

Silylborates (Li[Ph_nMe_3-nSiBPh₃], n = 1−3) and germylborates (Li[Ph_nMe_3-nGeBPh₃], n = 1−3; M[Et₃GeBPh₃], M = 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, ¹³C, ¹¹B, and ⁷Li NMR spectroscopic methods. The solid-state structure of germylborates Li[Ph₃GeBPh₃] and M[Et₃GeBPh₃] (M = Li and Na) were determined by X-ray diffraction analyses. The polymeric structure of M[Et₃GeBPh₃] was observed in the solid state and in hydrocarbon solution. The alkali metal atoms were located near the center of the benzene ring of triphenylborane and interacted with the neighboring borate molecules by Li⁺−π interaction. The polymeric structure was broken by the addition of MeOH. However, M[Et₃GeBPh₃] was coordinated by three MeOH molecules to form a dimeric structure without methanolysis reaction. The primary processes in photochemical reactions of silyl- and germylborates were investigated by chemical trapping experiments and the CIDEP (chemical-induced dynamic electron polarization) method. The cleavage of the Ge−B (or Si−B) bonds of germylborates (or silylborates) was considered most probably to occur from their triplet states.