Synthesis and Photochemistry of Tris(trimethoxysilyl)acyl-silanes and 1,4-Tetrakis(silyl)-1,4-bisacylsilanes.

In this contribution, we present the synthesis of two groups of novel acylsilanes -. Compounds and represent tris(trimethoxysilyl)acylsilanes, and compounds - are 1,4-tetrakis(silyl)-1,4-bisacylsilanes. All isolated compounds were characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy and X-ray crystallography. Additionally, these compounds were further analyzed by ultraviolet/visible (UV/vis) spectroscopy and their longest wavelength absorption bands were assigned by density functional theory (DFT) calculations. On the basis of the well-known Brook rearrangement of acylsilanes, we irradiated - in benzene solutions at 405 nm (λ) for several hours. Photolysis of compounds and afforded the same silene rearrangement products as found in previous investigations of structurally related acylsilanes. In addition, trapping experiments with MeOH further support our proposed mechanism for silene formation. The photolysis of tetrakis(trimethylsilyl)bisacylsilane gave rise to the formation of a monosilene intermediate ; upon prolonged irradiation, the subsequently formed bissilene undergoes a fast dimerization to bicyclic product . Interestingly, unlike the expected head-to-head dimerization of Brook-type silenes, this bissilene undergoes a selective head-to-tail dimerization. In contrast, tetrakis(trimethylsilyl)bisacylsilane undergoes a selective and completely stereoselective double CH activation to air stable bicyclic system . The mechanism of this rearrangement is fully described by DTF calculations. Unfortunately, tetrakis(trimethoxysilyl)bisacylsilanes and underwent unselective photochemical rearrangements.