Polymethylhydrosiloxane hydrosilylation

Beller and coworkers reported hydrosilylation reactions of organic carbonyl compounds such as ketones and aldehydes catalyzed by Fe(OAc)2 with phosphorus ligands (Scheme 21). In case of aldehydes as starting materials, the Fe(OAc)2/PCy3 with polymethylhydrosiloxane (PMHS) as an H-Si compound produced the corresponding primary alcohols in good to excellent yields under mild conditions [67]. Use of other phosphorus ligands, for instance, PPhs, bis(diphenylphosphino) methane (dppm), and bis(diphenylphosphino)ethane (dppe) decreased the catalytic activity. It should be noted that frans-cinnamaldehyde was converted into the desired alcohol exclusively and 1,4-reduction products were not observed. 

In 2005, Riant et al. reported the synthesis of a new air-stable S/N-chelating zinc catalyst, depicted in Scheme 10.50, which was fully characterised by all spectroscopic methods. This complex, prepared from the corresponding ferrocene oxazoline, was applied to the enantioselective hydrosilylation of ketones in the presence of polymethylhydrosiloxane, PMHS, providing modest enan-tioselectivities (<55% ee). ... 

The situation for the hydrosilylation of C = N functions with regard to ecology and economy is somewhat similar as for the hydride reduction, except that fewer effective catalytic systems have been developed [91]. Despite some recent progress with highly selective Ti-based [92] and Cu-based [93] catalysts using cheap polymethylhydrosiloxane as reducing agent, hydrosilylation will see its major applications in small-scale laboratory synthesis. 

PMHS corresponding polymeric reagent (PMHS, polymethylhydrosiloxane), a substantial rate increase was observed over the monomeric model (complete reduction of acetophenone in less than 1 min with PMHS vs. only 60% conversion in 1 h with (EtO)2SiHMe) [55]. The related hydrosilylation of 86 by chiral PTC uses an interesting ep/iedra-derivedhalometallated catalyst 25 (Scheme 10.12) [56],... 

The combination of polymethylhydrosiloxane (PMHS) and catalytic amounts of TBAF (1 mol%) and Cp2Ti(OC6H4Cl-4)2 (2 mol%) provides an efficient and convenient method for the partial reduction of lactones 187 to lactols 189 via hydrosilylation and subsequent hydrolysis of the resulting O-silyllactols 188 (equation 76)184. 

Polysiloxane-fluoro copolymers with low dielectric constants are prepared through hydrosilylation of 1,3,5-[CH2=CHCH20C(CF3)2]3C6H3 with polymethylhydrosiloxane catalyzed by Cp2PtCl2280. 

The hydrosilylation of carbonyl compounds with polymethylhydrosiloxane (PMHS) or other alkoxysilanes can be catalyzed by TBAF with high efficiency [20]. The asymmetric version of this process has been developed by Lawrence and... 

Hydrosilylation of ketones, and also of a- and /i-kclo esters and amides, has been achieved using polymethylhydrosiloxane in methanol, with various zinc(II) catalysts.277 The reactions are faster than in aprotic solvents, and show some enantios-electivity with chiral diaminozincs. 

The hydrosilylation of carbonyl compounds with polymethylhydrosiloxane (PMHS) or other alkoxysilanes can be catalyzed by TBAF, at high efficiency [9]. The asymmetric version of this process has been developed by Lawrence and coworkers using chiral ammonium fluoride 7c prepared via the method of Shioiri [10]. The reduction of acetophenone was performed with trimethoxysilane (1.5 equiv.) and 7c (10 mol%) in THF at room temperature, yielding phenethyl alcohol quantitatively with 51% ee (R) (Scheme 4.6). A slightly higher enantioselectivity was observed in the reduction of propiophenone. When tris(trimethylsiloxy)silane was used as a hydride source, the enantioselectivity was increased, though a pro-... 

It is well known that hydrosilylation processes usually catalyzed by Pt and Rh complexes can be efficiently applied in polymer chemistry. Ru3(CO)12 was effectively used for the functionalization of polysiloxanes via hydrosilylation of allyl derivatives with polymethylhydrosiloxanes [175]. On the other hand, polymerization via coupling of activated aromatics with dienes occurs mostly in the presence of ruthenium complexes as catalysts (Eq. 111). For representative references see Ref. [176] and papers cited therein. 

Reductive TVansformations. The utility of 1 was first demonstrated in the enantioselective hydrosilylation of ketones. Uniformly high enantioselectivity, yield, and turnover were observed for aromatic (and some aliphatic) ketones when using the complex derived from RhCls (eq 1). Lower enantioselection is observed with t-Bu-pybox or i-Pr-pybox cobalt(I). The derived l Sn(OTf)2 complex gives alcohol products with up to 58% ee using methano-lic polymethylhydrosiloxane. A cationic ruthenium(III) catalyst diverts the usual reduction pathway to enolsilane formation, particularly when the nature of the silane is modified (eq 2). ... 

There are several short reviews of the synthetic chemistry [15, 16] and physical properties for siloxane-alkylene oxide copolymers 3. The synthesis generally proceeds through two steps, the production of polymethylhydrosiloxane-dimethylsiloxane copolymers and the subsequent platinum catalyzed hydrosilylation of an allyl terminated polyether (Eq. 3). 

Zhang X-C, Wu F-F, Li S, Zhou J-N, Wu J, Li N, Fang W, Lam KH, Chan ASC (2011) Copper-dipyridylphosphine-polymethylhydrosiloxane a practical and effective system for the asymmetric catalytic hydrosilylation of ketones. Adv Synth Catal 353 1457-1462. doi 10. 1002/adsc.201100105... 

Hydrosilylation has been used to attach Choi or menthol moieties to polysiloxanes [162-168]. In most cases, double bonds are introduced to the terpenes at the OH position with a spacer (Fig. 7), and then the modified monomers are grafted onto polysiloxanes with Si-H moieties, i.e., polymethylhydrosiloxane. Hexachloroplatinate hydrate has been used as catalyst with usually a little excess of the olefin. The degree of hydrosilylation varies from ca. 50 to 100%, depending on monomers and their combinations. Thermal, optical, and mechanical properties, with emphasis on the LC phase transition, of the terpene-modified polysiloxanes have been studied and modulated with different alkyl spacers, comonomers... 

Other procedures for carbonyl hydrosilylation of aldehydes and ketones are using [bis(imino)pyridine]iron dinitrogen and dialkyl complexes as precatalysts. Only 0.1-1.0 mol% catalyst are required to achieve this transformation. The reductants are either phenylsilane or diphenylsilane in this case. A number of enantioselective versions of the hydrosilylation reaction is described. This includes the application of 1,2-bis[(25, 55)-2,5-dimethylphospholano]benzene [(S,5)-Me-DuPhos] (Scheme 4-328) as chiral ligand, iron(II) acetate as a precatalyst and polymethylhydrosiloxane as hydride source. A large variety of ketones can be transformed into the corresponding alcohols in excellent yield and up to 99% enantiomeric excess. Catalytic ketone hydrosilylation is also achieved with the dialkyliron complexes (S,S)-... 

Synthesis of the precursor necessary for the preparation of the siloxanic proton-conducting materials [I] and [II]. (a) Preparation of allylsulphonylchloride (b) hydrosilylation of allylsulphonylchloride and allyidimethylchlorosilane using polymethylhydrosiloxane reproduced from Di Noto and Vittadello (2005) by permission of Elsevier. 

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