Hydrosilylations intermolecular

These transformations take advantage of the knowledge obtained from well-established intermolecular reactions (metal-catalyzed hydrosilylation, borostannylation, etc.) and operate in a way that functionalizes both ends of the two unsaturated partners (enyne in this section) in the same manner as in the parent intermolecular reaction.264,265... 

Recently, the dissimilar complex [RuCl2(p-cymene)]2 has also demonstrated excellent selectivity for the (Z)-vinylsilane products for a variety of substrates (see Table 5). Whether or not this complex also acts as a monohydride-type hydrosilylation catalyst—as do the vast majority of well understood systems—is an open question. The selectivities for (Z)-/3-vinylsilane products are some of the best yet reported, especially for a-branched substrates (entry 4). From a synthetic point of view, the catalyst is exciting, but at present is limited to trialkyl- and triphenylsilanes in intermolecular applications (see Scheme 21), presenting problems for some applications. 

Intermolecular Hydrosilylation of Internal Alkynes 10.17.3.5.1 Yttrium catalysts for regiocontrol based on sterics... 

In the above-menhoned report [26], it was also shown that complex 20 catalyzed the intermolecular tandem alkyne hydroaminahon/hydrosilylation... 

In sharp contrast to simple alkenes that undergo silylcarbonylation, genuine silylformylation of an olefinic moiety is attained only by an intramolecular technique (Equation (33)). Since the most serious competitive reaetion is an intermolecular hydrosilylation reaction to form 192, the key for the successful transformation depends on an appropriate combination of substituents R and R. ... 

Internal acetylenes, Ni-mediated reactions, 10, 546 Internal alkenes, ethylene co-polymers, 4, 1145 Internal alkynes in alder-ene reaction, 10, 567 intermolecular hydrosilylation with ruthenium, 10, 802 with yttrium, 10, 801 silylboration, 9, 163 silylformylation, 11, 483... 

In 1994, Rubinsztajn reported the hyperbranched hydrosilylation polymerization of the AB3 carbosiloxane monomers 9 and 10181. Since intramolecular cyclization of these monomers would lead to more highly strained five-membered rings, it was expected that intermolecular reaction would be preferred. This was indeed the case, and molecular weights were highest when polymerizations were performed in bulk. Furthermore, slow addition of monomer resulted in polymers of much higher molecular weight. Functionalization of the polymers could be performed via hydrosilylation reactions, although these... 

The cationic [Cp Ru(MeCN)3]+(PF6) complex, reported as a stereoselective catalyst for trans hydrosilylation of internal alkynes, has been successfully used in intermolecular endo-dig hydrosilylation of propargyloxyhydrosilanes synthesized in situ via silylation of propargylic alcohols by tetramethyldisilazane [116]. 

Seyferth and Wiseman reacted as-obtained silazanes with catalytic amounts of potassium hydride, KH. They observed dehydrocoupUng of Si-H with N-H units and proposed a mechanism involving silylene-imine Si=N motifs as key species which rapidly add Si-H intermolecularly in hydrosilylation-type reactions. There has been, until now, no experimental proof for the proposed mechanism. Alternatively, a mechanism excluding silylene-imine formation was suggested... 

Compounds 1-4, 7-13, and 16 should be appropriate as monomeric precursors for modified PA-MPs, whereas the derivatives 17, 20, and 23 must be polymerized previously. The polymerization can be carried out either dehydrogenative (compounds 20 and 23) by the use of transition metal complex catalysts or by intermolecular hydrosilylation of Si-H to the -C=C- unit (compound 17) to yield crosslinked polymeric precursors for Si-alloyed PA-MPs. 

Hydrosilylation of unsaturated organosilicon compounds has also found several applications in molecular and polymer organosilicon chemistry. In particular, the addition of polyfunctional silicon hydrides to poly(vinyl)organosiloxane, catalyzed exclusively by Pt compounds and providing an activated cure for silicon rubber [10], has been of great practical importance. Hydrosilylation of the vinyl group at silicon seems to be effective synthetic method for preparation of oligomers and polymers with a linear or cyclolinear stmcture (polyhydrosilylation), and can occur either via the addition of dihydro-carbosilanes and -siloxanes to divinyl-silanes and -siloxanes [25, 26] or by intermolecular hydrosilylation [4] (eq. (1)). 

Generally, alkenylsilanes with an internal >C=C< bond are inert toward intermolecular hydrosilylation under mild conditions. No ring closure occurs when a short alkenyl substituent is present on the silicon atom of the substrate (eq. (3)) (e. g., [29]). 

Intermolecular hydrosilylation of diethynylsilanes with dihydro-substituted silicon compounds gives high molecular weight polymers -SiR2CH=CH- (e. g., [30]). The polymeric products obtained in the above-mentioned reactions are suitable substrates for ceramic and optoelectronic materials. 

Noteworthy, the stereochemistry of the vinyl moiety in both products was found to be that resulting from a trans addition to the triple bond, in contrast to the cis addition products expected from a concerted single-metal insertion.[67] This suggests that insertion reactions leading to trans addition products are entirely feasible in dinuclear species, probably as a consequence of the concerted action of both metal centers. This observation may be relevant in the context of some catalytic processes, such as alkyne hydrosilylations, which rather frequently afford trans addition products.[68] This unusual selectivity might result from intermolecular hydride transfer steps, similar to those recognized during catalytic hydroformylations,[69] or from the formation of dinuclear active species under catalytic conditions.[70]... 

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