Dichotomous Si–H Bond Activation by Alkoxide and Alcohol in Base-Catalyzed Dehydrocoupling of Silanes

Abstract

The activation of silanes in dehydrogenative coupling with alcohols under general base catalysis was studied experimentally (using multinuclear NMR, IR, and UV−visible spectroscopies) and computationally (at DFT M06/6-311++G(d,p) theory level) on the example of Ph 4-n SiH n (n = 1−3) interaction with (CF 3 ) 2 CHOH in the presence of Et 3 N. The effect of the phenyl groups' number and H − substitution by the electron-withdrawing (CF 3 ) 2 CHO − group on Si−H bond hydricity (quantified as hydride-donating ability, HDA) and Lewis acidity of silicon atom (characterized by maxima of molecular electrostatic potential) was accessed. Our results show the coordination of Lewis base (Y = Me 3 N, ROH, OR − ) leads to the increased hydricity of pentacoordinate hypervalent Ph 4-n Si(Y)H n complexes and a decrease of the reaction barrier for H 2 release. The formation of tertiary complexes [Ph 4-n Si(Y)H n ]•••HOR is a critical prerequisite for the dehydrocoupling with alkoxides being ideal activators. The latter can be external or internal, generated by in situ HOR deprotonation. The mutual effect of tetrel interaction and dihydrogen bonding in tertiary complexes (RO − )Ph 4-n SiH n •••HOR leads to dichotomous activation of Si−H bond promoting the proton−hydride transfer and H 2 release.

Selectivity of dehydrogenative silicone–oxygen bond formation in diphenylsilane by base and base‐activated catalysts

“…Amines have been shown to be reasonable for the dehydrogenation catalysts for phenyl silanes, with the general belief that a protonated amine-deprotonated hydroxyl form an ionic pair that acts as the active catalyst. 20,24 The employment of amines as catalysts provides higher selection of solubility and lower basicity compared to hydroxide and alkoxide salts. To understand if cation effects impact amines, six amines were chosen as dehydrogenation catalysts with increasing alkyl substitution and steric conges-tion.…”

“…As an attractive alternative to chlorosilanes, the Si-H bond in silanes can be readily activated at facile conditions in the presence of many catalysts for silyl ether formation but with the strong advantage of hydrogen gas as the only byproduct. [20][21][22][23][24][25][26][27][28] Employment of dihydrosilanes, which have two reactive hydrogens, expand utility by minimizing raw material usage, protection of diols, coupling of diols to form copolymers and rapid, facile synthesis of the cyclic siloxanes. 20,26 A frequently overlooked method for employing silyl ether formation by silane dehydrogenation is the use of alkaline conditions.…”

Unraveling a Biomass-Derived Multiphase Catalyst for the Dehydrogenative Coupling of Silanes with Alcohols under Aerobic Conditions

“…Subsequently, the nucleophilic attack of the alkoxy species derived from the alcohol to the electrophilic Si atom of the silyl–metal hydride intermediate would generate the corresponding silyl ether and molecular H 2 as well as the recovering of the oxygen activated Ag surface species. It should be noted that, according to the work of Belkova, Shubina, and coworkers, the silane activation could also be accounted by coordination of the previously formed alkoxide ionic species yielding hypervalent pentacoordinate silicon complexes, − which enable the formation of dihydrogen-bonded (MeO)­R 3 SiH···HOMe species, making the proton–hydride transfer and H 2 formation straightforward.…”

The Reaction of Hydrogen Halides with Tetrahydroborate Anion and Hexahydro-closo-hexaborate Dianion

“…In the present manuscript, the calculations were performed at the DFT/M06/6-311++G(d,p) level for comparison to the hydride donor ability (HDA) values of boron hydrides and other main group hydrides, as previously calculated by the same method [ 28 , 30 , 73 ]. Additionally, the values obtained can be used as a reference for assessing the effectiveness of the B–H bond activation by transition metals.…”