Selective Enzymatic Oxidation of Silanes to Silanols

Compared to the biological world's rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wild‐type cytochrome P450 monooxygenase (P450_(BM3) from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to give silanols. Directed evolution was applied to enhance this non‐native activity and create a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as the terminal oxidant. The evolved enzyme leaves C−H bonds present in the silane substrates untouched, and this biotransformation does not lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the native C−H hydroxylation mechanism of the P450 enzyme. This enzymatic silane oxidation extends nature's impressive catalytic repertoire

Hydrosilylation of 1-alkenes with dichlorosilane

Symmetrically and unsymmetrically substituted diorganodichlorosilanes have been prepared by hydrosilylation with dichlorosilane using two different platinum catalysts, i.e., hexachloroplatinic acid (Speier's catalyst) and a platinum cyclovinylmethylsiloxane complex. Hydrosilylation of unsubstituted 1-alkenes proved to be very efficient, yielding anti-Markonikov substituted di-n-alkyldichlorosilanes. However, no reaction was observed when electron-deficient 1-alkenes were used. Octacarbonyldicobalt enabled formation of the monoadduct of 1H,1H,2H-perfluoro-1-hexene with dichlorosilane, which was employed in a second hydrosilylation of the olefin. Thus, the anti-Markovnikov diadduct was obtained in 40% overall yield. The two-step synthesis has also been applied successfully to obtain unsymmetrically substituted diorganodichlorosilanes containing nitrile and ether groups

A unified survey of Si-H and H-H bond activation catalysed by electron-deficient boranes

The bond activation chemistry of B(C6F5)(3) and related electron-deficient boranes is currently experiencing a renaissance due to the fascinating development of frustrated Lewis pairs (FLPs). B(C6F5)(3)'s ability to catalytically activate Si-H bonds through eta(1) coordination opened the door to several unique reduction processes. The ground-breaking finding that the same family of fully or partially fluorinated boron Lewis acids allows for the related H-H bond activation, either alone or as a component of an FLP, brought considerable momentum into the area of transition-metal-free hydrogenation and, likewise, hydrosilylation. This review comprehensively summarises synthetic methods involving borane-catalysed Si-H and H-H bond activation. Systems corresponding to an FLP-type situation are not covered. Aside from the broad manifold of C=X bond reductions and C=X/C-X defunctionalisations, dehydrogenative (oxidative) Si-H couplings are also included.DFG, EXC 314, Unifying Concepts in Catalysi

Seeking for ultrashort "non-bonded" hydrogen-hydrogen contacts in some rigid hydrocarbons and their chlorinated derivatives

In this communication a systematic computational survey on some rigid hydrocarbon skeletons, e.g. half-cage pentacyclododecanes and tetracyclododecanes, and their chlorinated derivatives in order to seek for the so-called ultrashort "non-bonded" hydrogen-hydrogen contacts is done. It is demonstrated that upon a proper choice and modifications of the main hydrocarbon backbones, and addition of some chlorine atoms instead of the original hydrogen atoms in parts of the employed hydrocarbons, the resulting strain triggers structural changes yielding ultrashort hydrogen-hydrogen contacts with inter-nuclear distances as small as 1.38 Angstrom. Such ultrashort contacts are clearly less than the world record of an ultrashort non-bonded hydrogen-hydrogen contact, 1.56 Angstrom, very recently realized experimentally by Pascal and coworkers in in,in-bis(hydrosilane) [J. Am. Chem. Soc. 135, 13235 (2013)]. The resulting computed structures as well as the developed methodology for structure design open the door for constructing a proper set of molecules for future studies on the nature of the so-called non-bonded hydrogen-hydrogen interactions that is now an active and controversial area of research.Comment: 17 pages, 2 figures, 3 Tables, Supporting informatio

Catalytic Dehydrogenative Coupling of Hydrosilanes with Alcohols for the Production of Hydrogen On-demand: Application of a Silane/Alcohol Pair as a Liquid Organic Hydrogen Carrier

The compound [Ru(p-cym)(Cl)2(NHC)] is an effective catalyst for the room-temperature coupling of silanes and alcohols with the concomitant formation of molecular hydrogen. High catalyst activity is observed for a variety of substrates affording quantitative yields in minutes at room temperature and with a catalyst loading as low as 0.1 mol %. The coupling reaction is thermodynamically and, in the presence of a Ru complex, kinetically favourable and allows rapid molecular hydrogen generation on-demand at room temperature, under air, and without any additive. The pair silane/alcohol is a potential liquid organic hydrogen carrier (LOHC) for energy storage over long periods in a safe and secure way. Silanes and alcohols are non-toxic compounds and do not require special handling precautions such as high pressure or an inert atmosphere. These properties enhance the practical applications of the pair silane/alcohol as a good LOHC in the automotive industry. The variety and availability of silanes and alcohols permits a pair combination that fulfils the requirements for developing an efficient LOHC

Transfer hydrosilylation

Transfer hydrogenation is without question a common technology in industry and academia. Unlike its countless varieties, conceptually related transfer hydrosilylations had essentially been unreported until the recent development of a radical and an ionic variant. The new methods are both based on a silicon-substituted cyclohexa-1,4-diene and hinge on the aromatization of the corresponding cyclohexadienyl radical and cation intermediates, respectively, concomitant with homo-or heterolytic fission of the Si-C bond. Both the radical and ionic transfer hydrosilylation are brought into context with one other in this Minireview, and early insight into the possibility of transfer hydrosilylation is included. Although the current state-of-the-art is certainly still limited, the recent advances have already revealed the promising potential of transfer hydrosilylation

Cyclopentadienyliron dicarbonyl dimer: A simple tool for the hydrosilylation of aldehydes and ketones under air

International audienceThe readily available iron complex [CpFe(CO)2]2 (1) exhibits good catalytic activity in the hydrosilylation of aldehydes and ketones in the presence of diethoxymethylsilane. The procedure described is air-tolerant and applicable to a wide range of substrate

Transferhydrosilylierung

Es steht außer Frage, dass Transferhydrierung ein gängiges Verfahren in der Industrie und der akademischen Welt ist. Trotz ihrer Vielfältigkeit war die konzeptionell verwandte Transferhydrosilylierung bis zur jüngsten Entwicklung einer radikalischen und einer ionischen Variante im Grunde unbekannt gewesen. Die neuen Methoden basieren beide auf dem Motiv eines siliciumsubstituierten Cyclohexa-1,4-diens und hängen von der Aromatisierung der entsprechenden radikalischen bzw. kationischen Cyclohexadienylzwischenstufen begleitet von homo- oder heterolytischer Spaltung der Si-C-Bindung ab. Die radikalische und ionische Transferhydrosilylierung werden in diesem Kurzaufsatz miteinander in Bezug gesetzt, und frühe Hinweise auf die Möglichkeit einer Transferhydrosilylierung werden auch berücksichtigt. Der derzeitige Stand der Forschung befindet sich zweifellos noch in den Anfängen, aber die jüngsten Fortschritte lassen das vielversprechende Potenzial von Transferhydrosilylierungen bereits erkennen