Transition‐Metal‐Free Cleavage of CO

Abstract

Tertiary silane 1H, 2‐[(diphenylsilyl)methyl]‐6‐methylpyridine, reacts with tris(pentafluorophenyl)borane (BCF) to form the intramolecular pyridine‐stabilized silylium 1+‐HBCF. The corresponding 2‐[(diphenylsilyl)methyl]pyridine, lacking the methyl‐group on the pyridine ring, forms classic N(py)→B adduct 2H‐BCF featuring an intact silane Si−H fragment. Complex 1+‐HBCF promotes cleavage of the C≡O triple bond in carbon monoxide with double C−Csp2 bond formation, leading to complex 3 featuring a B‐(diarylmethyl)‐B‐aryl‐boryloxysilane fragment. Reaction with pinacol generates bis(pentafluorophenyl)methane 4 as isolable product, proving the transition‐metal‐free deoxygenation of carbon monoxide by this main‐group system. Experimental data and DFT calculations support the existence of an equilibrium between the silylium–hydroborate ion pair and the silane–borane mixture that is responsible for the observed reactivity.

B(C6F5)3‐Catalyzed sp3 C—Si Bond Forming Consecutive Reactions

“…Significantly, 19 F{ 1 H} NMR of the crude reaction mixture exhibited one set of major signals assignable to an N ‐silylpiperidinium borohydride, suggesting that the piperidinium ion species with (C 6 F 5 ) 3 BH – counteranion is in a resting state (Scheme a). In consistent with this observation, a stoichiometric reaction of the piperidine (1 equiv), B(C 6 F 5 ) 3 (1 equiv), and MePhSiH 2 (5 equiv) generated the corresponding N ‐silyl piperidinium borohydride in quantitative yield within 10 min at 25 °C,[27a, 45] corroborating facile formation of the predominant resting species during the borane catalysis (Scheme b).…”

An Experimental Acidity Scale for Intramolecularly Stabilized Silyl Lewis Acids

“…In many cases, this was achieved by intramolecular coordination of weak Lewis bases (LB) to the cationic silicon center that results in tetra‐coordination for the silicon center (Figure ). In saying that, the parallels to intramolecular Frustrated Lewis Pairs (FLPs) popularized by Erker and Stephan become obvious . The strength of the LA/LB interaction determines structure, spectroscopic properties and, in the context of this report most important, the Lewis acidity of these species.…”

Electrophilic Formylation of Arenes by Silylium Ion Mediated Activation of Carbon Monoxide

“…[12] Considering the strong Lewis acidity of silylium ions [R 3 Si] + [WCA] À (WCA = weakly coordinating anion), [13] we have been interested in investigating the electrophilic activation of CO by these highly reactive intermediates (Scheme 1, bottom). [14,15] Ther eaction of silylium ions and CO had already been studied by quantum-chemical and mass-spectrometric analyses in the gas phase. [16] [Me 3 Si(CO)] + was found to be 11.3 kcal mol À1 more stable than [Me 3 Si(OC)] + but an equilibrium of the two cations in the condensed phase cannot be ruled out.…”