Hydrides silyl

THP ethers can be converted directly to TBDMS and TES ethers using the silyl hydride and Sn(OTf)2 or the silyl triflate (70-95% yield). The use of TMSOTf gives the free alcohols upon isolation. ... 

The reaction of CpFe(CO)2Me with R3SiH gives the bis(silyl)hydride complex 21. Photoreaction of 21 in DMF afforded the corresponding disiloxane (Scheme 52). We believe that the oxygen in the disiloxane is derived from DMF, because NMes is concomitantly formed in this reaction. It is considered that the silyl species a, which is prepared via reductive elimination of RsSiH from 21 in situ, is the active species within the catalytic cycle. Therefore, the generation of a bis(silyl)hydride species is the dormant step. We are currently studying the details of the reaction mechanism. 

Further reactions of 5/6 with the sterically less bulky silanes HSiCl3, Ph2SiHCl and Ph2SiH2 give the thermo-labile /x-biscarbyne complex 14, which has been spectroscopically characterized (Table 1). In these cases, formation of the silyl hydrides 11, 13, 15 and 16 as products of an oxidative addition at the 16e -complex generated from 6 (attack at Mn) becomes important. 

The variation of the substituent pattern of the introduced silane provides further insight into the reaction mechanism of the CO activation process of scheme 2 (Table 1) The yield of ju-carbyne-complex (O-attack of the silane) compared to silyl hydride formation (Mn-attack of the silane) is a function of the Lewis-acidity of the silane. However, even with the strongly acidic HSiCl3 as reagent, the product ratio 12/13 is still 1 9. 

Previous investigations of the photolysis reactions of 5 in the presence of various silanes only showed the products of Si-H activation [20], Metal silyl hydride formation, however, becomes the main reaction path with sterically less hindered silanes [21]. 

Reduction to Alcohols. The organosilane-mediated reduction of ketones to secondary alcohols has been shown to occur under a wide variety of conditions. Only those reactions that are of high yield and of a more practical nature are mentioned here. As with aldehydes, ketones do not normally react spontaneously with organosilicon hydrides to form alcohols. The exceptional behavior of some organocobalt cluster complex carbonyl compounds was noted previously. Introduction of acids or other electrophilic species that are capable of coordination with the carbonyl oxygen enables reduction to occur by transfer of silyl hydride to the polarized carbonyl carbon (Eq. 2). This permits facile, chemoselective reduction of many ketones to alcohols. 

This insertion is so efficient that silyl hydrides are used for silylene detection. 

Shortened M-Si bonds Long Si-X bonds Si-H contacts of 1.8-2.1A Small Si-M-Si angles in bis(silyl)hydride systems X and H substituents in the apical positions in respect to silicon atom Elongated M-H bonds Elongated M-Si bonds Normal Si-X bonds Si-H contacts of 1.7-1.8 A No regulations No regulations Normal M-H bonds... 

Tamao and Ito proposed a mechanism for the nickel-catalyzed cyclization/hydrosilylation of 1,7-diynes initiated by oxidative addition of the silane to an Ni(0) species to form an Ni(ii) silyl hydride complex. Gomplexation of the diyne could then form the nickel(ii) diyne complex la (Scheme 1). Silylmetallation of the less-substituted G=C bond of la, followed by intramolecular / -migratory insertion of the coordinated G=G bond into the Ni-G bond of alkenyl alkyne intermediate Ila, could form dienylnickel hydride intermediate Ilia. Sequential G-H reductive elimination and Si-H oxidative addition would release the silylated dialkylidene cyclohexane and regenerate the silylnickel hydride catalyst (Scheme 1). 

Ojima has proposed a mechanism for the rhodium-catalyzed cyclization/hydrosilylation of enynes initiated by oxidative addition of the H-Si bond of the hydrosilane to form the Rh(iii) silyl hydride complex If (Scheme 7). Silylmetallation of the G=G bond of the enyne coupled with coordination of the pendant G=G bond could form... 

METHOXYCARBONYL-1,1,6-TRIMETHYL-1,4,4a,5,6,7,8,8a-OCTAHYDRO-2,3-BENZOPYRONE, an intramolecular Diels-Alder reaction is responsible for the diastereoselectivity. The stereoselective 1,4-functionalization of 1,3-dienes is exemplified by a two-step process leading to cis- and trans-1-ACETOXY-4-(DICARBOMETHOXYMETHYL)-2-CYCLOHEXENE. The effectiveness of a silyl hydride in providing a means for erythro-directed reduction of a p-keto amide is applied in a route to ERYTHRO-1 -(3-HYDROXY-2-METHYL-3-PHENYL-PROPANOYLJPIPERIDINE. This is followed by an asymmetric synthesis based on a chiral bicyclic lactam leading to (R)-4-ETHYL-4-ALLYL-2-CYCLOHEXEN-1-ONE. The stereoselectivity with which acetoxy migration can operate to an adjacent radical center is reflected in the one-step reaction that gives rise to 1,3,4,6-TETRA-O-ACETYL-2-DEOXY-a-D-GLUCOPYRANOSE. 

High-valent rhenium silyl hydrides ReH5(PPh(Pr-i)2)2(SiHPh2)2 (27) and ReHsO CysL (SiH2Ph)2 have been characterized by neutron and X-ray diffraction, respectively. The complexes were prepared from the corresponding hydrides ReH7(PPh(Pr-/)2)2 and... 

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