Direct observation of a borane–silane complex involved in frustrated Lewis-pair-mediated hydrosilylations

Houghton, Adrian Y.; Hurmalainen, Juha; Mansikkamäki, Akseli; Piers, Warren E.; Tuononen, Heikki M.

doi:10.1038/nchem.2063

Cited by 350 publications

(225 citation statements)

References 53 publications

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“…Notably however, two examples of adducts of main group Lewis acids (boranes and alanes) with silanes were recently isolated and structurally characterized. [27,28] These structures mark an exciting advance in the study of main group-catalyzed hydrosilations by providing the first direct evidence for η 1 -silane intermediates in main group chemistry. These advances, described below, offer the opportunity for direct structural comparison of these electrophilic silicon species with those involving transition metals.…”

Section: Main Group Lewis Acid Catalystsmentioning

confidence: 98%

“…Mechanistic comparisons of electrophilic silane activations are enabled by major recent advances that elucidate the structures of key silicon intermediates. For example, borane-silane [27] and alane-silane [28] adducts have only recently been isolated and characterized, and these studies provide definitive support for intermediates that had long been inferred based on indirect experimental evidence. Similarly, structural data was recently obtained for a cationic ruthenium silylene complex that catalyzes olefin hydrosilation reactions.…”

Section: Reviewmentioning

confidence: 99%

“…Thus, it is notable that an adduct between triethylsilane and 1,2,3-tris(pentafluorophenyl)-4,5,6,7-tetrafluoro-1-boraindene (2) was recently characterized in solution and in the solid state (Scheme 6). [27] [36] and B-H distances of perfluorohydridoborate anions are 1.14 Å [37] Although hydrosilation studies were not reported for 2, initial indications are that the coordinated silane is electrophilic. Adduct 2•HSiEt3 reacted with bis(triphenylphosphine)iminium chloride, [PPN][Cl], to form a hydridoborate compound by Si-H cleavage and formation of Et3Si-Cl (Scheme 7).…”

Section: Reviewmentioning

confidence: 99%

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Electrophilic Activation of Silicon–Hydrogen Bonds in Catalytic Hydrosilations

2017

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Hydrosilation reactions represent an important class of chemical transformations and there has been considerable recent interest in expanding the scope of these reactions by developing new catalysts. A major theme to emerge from these investigations is the development of catalysts with electrophilic character that transfer electrophilicity to silicon via Si-H activation. This type of mechanism has been proposed for catalysts ranging from Group 4 transition metals to Group 15 main group species. Additionally, other electrophilic silicon species, such as silylene complexes and η 3 -H2SiRR' complexes, have been identified as intermediates in hydrosilation reactions. In this Review, different types of catalysts are compared to highlight the range of hydrosilation mechanisms that feature electrophilic silicon centers, and the importance of these catalysts to the development of new hydrosilation reactions is discussed.

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Section: Main Group Lewis Acid Catalystsmentioning

confidence: 98%

Section: Reviewmentioning

confidence: 99%

Section: Reviewmentioning

confidence: 99%

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Electrophilic Activation of Silicon–Hydrogen Bonds in Catalytic Hydrosilations

2017

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“…In the absence of an appropriate nucleophile no silylium ions are formed from combining B(C 6 F 5 ) 3 and R 3 SiH, although silane H/D scrambling still proceeds via a four‐membered transition state (inset Scheme 1). 7 …”

Section: Introductionmentioning

confidence: 99%

N‐Methyl‐Benzothiazolium Salts as Carbon Lewis Acids for Si−H σ‐Bond Activation and Catalytic (De)hydrosilylation

Fasano

Radcliffe

Curless

et al. 2016

Chemistry A European J

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N−Me‐Benzothiazolium salts are introduced as a new family of Lewis acids able to activate Si−H σ bonds. These carbon‐centred Lewis acids were demonstrated to have comparable Lewis acidity towards hydride as found for the triarylboranes widely used in Si−H σ‐bond activation. However, they display low Lewis acidity towards hard Lewis bases such as Et3PO and H2O in contrast to triarylboranes. The N−Me‐benzothiazolium salts are effective catalysts for a range of hydrosilylation and dehydrosilylation reactions. Judicious selection of the C2 aryl substituent in these cations enables tuning of the steric and electronic environment around the electrophilic centre to generate more active catalysts. Finally, related benzoxazolium and benzimidazolium salts were found also to be active for Si−H bond activation and as catalysts for the hydrosilylation of imines.

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“…Inspired by these recent advances and realizing (i) the ability of triphenylboron hydrides to activate CO 2 and carbonyl groups owing to the reactive B−H bond,16 and (ii) the well‐known ability of mixtures of silanes and B(C 6 F 5 ) 3 to promote hydrosilylation reactions of unsaturated substrates via formation of silyl cations,17, 18 we sought to develop a reactive Si−B system that would be capable of CO activation (Scheme 1, bottom). Although the chemistry and catalysis with electrophilic silylium species is rapidly gaining attention,19 examples of frustrated Lewis pair‐type chemistry involving silicon are relatively rare 20…”

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confidence: 99%

Transition‐Metal‐Free Cleavage of CO

Devillard

Bruin

Siegler

et al. 2017

Chemistry A European J

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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.

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Direct observation of a borane–silane complex involved in frustrated Lewis-pair-mediated hydrosilylations

Cited by 350 publications

References 53 publications

Electrophilic Activation of Silicon–Hydrogen Bonds in Catalytic Hydrosilations

Electrophilic Activation of Silicon–Hydrogen Bonds in Catalytic Hydrosilations

N‐Methyl‐Benzothiazolium Salts as Carbon Lewis Acids for Si−H σ‐Bond Activation and Catalytic (De)hydrosilylation

Transition‐Metal‐Free Cleavage of CO

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