From Intramolecularly [4 + 1]- and [4 + 2]-Coordinated Tri- and Tetraorganosilanes to Hypercoordinated Benzoxasilaphospholes

摘要

The synthesis of the intramolecularly coordinated triorganosilane {4-t-Bu-2,6-[P(O)(OEt)_2]_2C_6H_2}Si(H)Ph_2 (3) is reported. The reaction of both 3 and the corresponding tetraorganosilane {4-t-Bu-2,6-[P(O)(OEt)_2]_2C_6H_2}SiPh_3 (2) with [Ph_3C]~+[PF_6]~- results in the in situ generation of the siliconium ion {4-t-Bu-2,6-[P(O)(OEt)_2]_2C_6H_2}SiPh_2~+PF_6~- (4). The siliconium ion of 4 reacts with water under intramolecular cyclization to give the novel hypercoordinated benzoxasilaphosphole [1(P),3(Si)-P(O)(OEt)OSiPh_2-6-t-Bu-4-P(O)(OEt)_2]C_6H_2 (5). Compound 5 and the related methyl/phenyl- and dimethyl-substituted derivatives [1(P),3(Si)-P(O)(OEt)OsiRR'-6-t-Bu-4-P(O)(OEt)_2]C_6H_2 (6, R = Me, R' = Ph; 7, R = R' = Me) are also prepared by reaction of {4-t-Bu-2,6-[P(O)(OEt)_2]_2C_6H_2}Li (1) with the corre-sponding dichlorodiorganosilanes. Compound 6 is a mixture of diastereomers from which the 1S, 3S diastereomer 6a was separated. In solution, the latter undergoes an acid-catalyzed epimerization which was monitored by ~(31)P NMR spectroscopy. The mechanism proposed to account for this process is supported by ab initio MO calculations. The molecular structures of 3, 5, and 6a were determined by single-crystal X-ray diffraction.