Hydrosilation catalyst

The most common oxidation states and corresponding electronic configurations of platiaum are +2 which is square planar, and +4 which is octahedral. Compounds in oxidation states between 0 and +6 [t) exist. Platiaum hydrosilation catalysts are used in the manufacture of siHcone polymers. Several platiaum coordination compounds are important chemotherapeutic agents used for the treatment of cancer. 

An important example in this context is the hydrosilation reaction [121]. Hydrosilation is the formal addition of a silane to an alkene in presence of a hydrosilation catalyst. This reaction has numerous applications e.g., with a suitable catalyst, an enantioselective hydrosilation is possible [122] and also hydrosilation and double hydrosilation of alkines [123] are known. 

Titanocene catalysts do not catalyze the hydrosilation of most internal olefins, although they can attach active olefins such as styrene, or norbornene to the growing polymer chain ends. The zirconocene-based catalysts, on the other hand, can be powerful hydrosilation catalysts and the remarkable copolymer synthesis shown in Equation 3 can be easily achieved under mild conditions (V7). 

Recently we found that freshly prepared nickel powder is an efficient hydrosilation catalyst when continuously irradiated(49). 

Previous work (48) with homogeneous analogues showed that Si-H oxidative additions yield cis products. A cis geometry of hydride and silyl may be allowed in catalytic hydrosilation. Because the industral homogeneous hydrosilation catalyst (62) is h PtClg we tested the activity of our surface generated reagent for the reaction of Equation 24. A suspension of the catalyst was irradiated in 1-... 

This method might suffer from lack in generality, because a reactive dye was used as a substrate. Control reactions proved that the relative order of reactivity of the identified hydrosilation catalysts is, however, identical when conventional unsaturated systems instead of the reactive dyes are employed. 

Cationic mthenium silylenoid complexes function as efficient hydrosilation catalysts. Tilley and Glaser reported that 1 mol% of 30 catalyzed the hydrosilation of... 

In addition to ruthenium, Tilley and coworkers also reported that cationic iridium silylenoid complexes were efficient olefin hydrosilation catalysts [reaction (7.6)].56 This silylene complex catalyzes the hydrosilation of unhindered mono- or disubsti-tuted olefins with primary silanes to produce secondary silanes with anti Markovni-kov selectivity. Iridium catalyst 32 exhibited reactivity patterns similar to those of ruthenium 30 only primary silanes were allowed as substrates. In contrast to 30, cationic iridium 32 catalyzed the redistribution of silanes. Exposing phenylsilane to 5 mol% of 32 in the absence of olefin produced diphenylsilane, phenylsilane, and silane. 

Rh(P2) 22+ dimers. The new [Rh(P2)(P)2]+ complexes can be isolated as their PFg- complexes. These Rh(I) complexes are air-stable in the solid state and serve as extremely active and selective (1,2- vs. 1,4-hydrosilation) asymmetric hydrosilation catalysts for the reduction of ketones with disubstituted silanes. 

Development of Tetraphosphine Rh(I) catalysts. The tetra(phosphine) rhodium(I) cations, prepared by adding stoichiometric amounts of a monophosphine to the ligand deficient dimers, were subsequently found to be very active hydrosilation catalysts. Although the addition of trisubstituted silanes was slow (1-2 days) and required elevated temperatures ( 55°C), high regioselectivity to the 1,2-hydrosilation products was obtained. Importantly, no products arising from catalyst deactivation in the form of trimeric rhodium(I) complexes were observed. More interestingly, these tetraphosphine rhodium complexes are extremely efficient catalysts for the 1,2-addition of disubstituted silanes to enolizable ketones. Turn-over numbers up to 105/hr at room temperature have been observed for a number of catalyst and ketone/silane combinations. 

Recently, a new class of platinum silyl complexes was reported (89-91). The complexes of type 49, formed from LPtfQH (L = bulky phosphine) and trialkylsilanes, are extremely efficient hydrosilation catalysts. Upon heating, 49 is converted into 50 via an ill-defined a-elimination process. In all examples of redistributions, the presence of at least one hydro-... 

The platinum catalyst is effective in very small amounts, and can be introduced as H2PtCl6 or as elemental platinum on an inert support. A particularly active catalyst is the soluble platinum complex of divinyltetramethyldisilox-ane, CH2=CHSiMe2-0-SiMe2CH=CH2. The hydrosilyla-tion reaction operates through the Chalk-Harrod mechanism or one of its variants. bz jn these mechanisms, the first step involves the conversion of a metal alkene complex to a metal alkene silyl hydride complex. In addition to platinum, recently ruthenium, rhodium, palladium, copper, and zinc complexes are being studied as hydrosilation catalysts. " ... 

Easy recycling of gold hydrosilation catalysts has also been achieved using a fluorous approach.Conversions varied from moderate to excellent for the reaction of dimethylphenylsilane with benzaldehyde. However, the mechanism is not clear at this stage. The catalyst could not be recycled in the absence of fluorous solvents under thermomorphic conditions and the formation of... 

Reactions of silanes are often best catalyzed by hydrosilation catalysts such as Pt or Pd. Similarly, C — H bonds are formed in the addition of phosphines or amines to C = C or C = C bonds. Reactions are catalyzed (acid, base, or metal) or free radical promoted, e.g. ... 

For this reason, the unsaturated hydride complex appears to behave as an efficient hydrosilation catalyst. ... 

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