Hydrosilylation-cross-coupling

Table 2 A tandem hydrosilylation cross-coupling approach to aryl olefins...

A comparison of the results obtained in hydroformylation with those of other not exhaustively investigated reactions4 , such as hydrosilylation, cross coupling, carbenoid reactions, shows that the necessity to achieve a steric control in the great number of catalytic steps under relatively severe temperature and pressure conditions considerably retards the progress in the field. 

The coupling products are obtained by one-pot hydrosilylation/cross-coupling of alkynes. Pt-catalyzed hydrosilylation of alkyne with tetramethyldisiloxane (52) generates the alkenylsilane 53, which is coupled with 4-iodoanisole (2) using ligandless Pd catalyst and TBAF at room temperature to afford 46 in 84 % yield [103]. 

Scheme 7.25 Intermolecular hydrosilylation/cross-coupling of terminal alkynes.

Scheme 7.28 Intramolecular hydrosilylation/cross-coupling of 3-pentyn-l-ol.

Scheme 7.29 Syn and anti intramolecular hydrosilylation/cross-coupling to generate substituted allylic alcohols.

One-Pot Sequential Hydrosilylation/Cross-Coupling Reaction. ( )-5-(4-Methoxy-phenyl]-4-penten-1-ol (96)... 

PLATINUM CATALYZED HYDROSILYLATION AND PALLADIUM CATALYZED CROSS-COUPLING ONE-POT HYDROARYLATION OF 1-HEPTYNE TO (E)-l-(l-HEPTENYL)-4-... 

Radical-mediated silyldesulfonylation of various vinyl and (a-fluoro)vinyl sulfones 21 with (TMSlsSiH (Reaction 25) provide access to vinyl and (a-fluoro)vinyl silanes 22. These reactions presumably occur via a radical addition of (TMSlsSi radical followed by /)-scission with the ejection of PhS02 radical. Hydrogen abstraction from (TMSlsSiH by PhS02 radical completes the cycle of these chain reactions. Such silyldesulfonylation provides a flexible alternative to the hydrosilylation of alkynes with (TMSlsSiH (see below). On oxidative treatment with hydrogen peroxide in basic aqueous solution, compound 22 undergoes Pd-catalyzed cross-couplings with aryl halides. 

Yamano T, Taya N, Kawada M, Huang T, Imamoto T (1999) Tetrahedron Lett 40 2577 Brunner H, Nishiyama H, Itoh K (1993) Asymmetric hydrosilylation. In Ojima I (ed) Catalytic asymmetric synthesis. Wiley-VCH, New York, chap 6 Sawamura M, Kuwano R, Ito Y (1994) Angew Chem, Int Ed Engl 33 111 Kuwano R, Uemura T, Saitoh M, Ito Y (1999) Tetrahedron Lett 40 1327 Hayashi T (1993) Asymmetric allylic substitution and grignard cross-coupling. In Ojima I (ed) Catalytic asymmetric synthesis. WUey-VCH, New York, chap 7-1 Trost BM, Vranken DLV (1996) Chem Rev 96 395 Consiglio G,Waymouth RM (1989) Chem Rev 89 257... 

The hydrosi(ly)lations of alkenes and alkynes are very important catalytic processes for the synthesis of alkyl- and alkenyl-silanes, respectively, which can be further transformed into aldehydes, ketones or alcohols by estabhshed stoichiometric organic transformations, or used as nucleophiles in cross-coupling reactions. Hydrosilylation is also used for the derivatisation of Si containing polymers. The drawbacks of the most widespread hydrosilylation catalysts [the Speier s system, H PtCl/PrOH, and Karstedt s complex [Pt2(divinyl-disiloxane)3] include the formation of side-products, in addition to the desired anh-Markovnikov Si-H addition product. In the hydrosilylation of alkynes, formation of di-silanes (by competing further reaction of the product alkenyl-silane) and of geometrical isomers (a-isomer from the Markovnikov addition and Z-p and -P from the anh-Markovnikov addition. Scheme 2.6) are also possible. 

Alkenylsiloxanes take part in cross-couplings as well. Hydrosilylation and cross-coupling can be combined in one pot to give an effective method of hydrocarbation of a triple bond (Equation (17)) 278... 

The formation of a cyclic siloxane obtained by intramolecular hydrosilylation has been used to control the stereochemistry of a cross-coupling reaction (Equation (18)) 79... 

A separate, quite thorough study of terminal alkyne hydrosilylation with platinum arrived at a similar set of conditions.39 This work utilized a one-pot hydrosilylation with the preformed platinum(O) complex (>Bu3P)Pt[(CH2=CH)Me2Si]20 ([(CH2=CH)Me2Si]20 = DVDS) and subsequent palladium-catalyzed coupling reaction to demonstrate that the platinum catalyst is compatible with cross-coupling conditions, providing a convenient hydrocarbation of terminal alkynes (Table 2). 

Denmark pursued intramolecular alkyne hydrosilylation in the context of generating stereodefined vinylsilanes for cross-coupling chemistry (Scheme 21). Cyclic siloxanes from platinum-catalyzed hydrosilylation were used in a coupling reaction, affording good yields with a variety of aryl iodides.84 The three steps are mutually compatible and can be carried out as a one-pot hydro-arylation of propargylic alcohols. The isomeric trans-exo-dig addition was also achieved. Despite the fact that many catalysts for terminal alkyne hydrosilylation react poorly with internal alkynes, the group found that ruthenium(n) chloride arene complexes—which provide complete selectivity for trans-... 

The Hiyama coupling offers a practical alternative when selectivity and/or availability of other reagents are problematic. Hiyama et al. coupled alkyltrifluorosilane 74 with 2-bromofuran 73 to give the corresponding cross-coupled product 75 in moderate yield in the presence of catalytic Pd(Ph3P)4 and 3 equivalents of TBAF [65]. In this case, more than one equivalent of fluoride ion was needed to form a pentacoordinated silicate. On the other hand, alkyltrifluorosilane 74 was prepared by hydrosilylation of the corresponding terminal olefin with trichlorosilane followed by fluorination with C11F2. This method provides a facile protocol for the synthesis of alkyl-substituted aromatic compounds. 

Ravlov, V. A Mechanism of Asymmetric Induction in Catalytic Hydrogenation, Hydrosilylation, and Cross-Coupling Reactions on Metal Complexes, Russ. Chem. Rev. 2002, 71, 39-56. 

As discussed above, the cross-coupling reaction of organosilicon compounds proceeds stereospecifically, depending on the reaction conditions. Thus, the transformation C—Si C —C is demonstrated to be accompanied by chirality transfer. Now, the question arises of how to prepare organosilicon compounds whose chiral allylic carbon is substituted by a silyl group. The most accessible solution is asymmetric hydrosilylation of olefins [35]. We studied asymmetric hydrosilylation of 1-substituted 1,3-butadienes using... 

Ferrocenyl-based ligands comprise a versatile class of auxiliaries because they can be easily modified at the benzylic position with retention of configuration and can incorporate both central and planar chiralities. The appropriate balance of steric and electronic factors has provided ferrocenyl derivatives featuring chelating P,N properties that proved beneficial in numerous enantioselective transformations [50]. Among more recent applications, they could be utilized very efficiently in Pd-catalyzed hydrosilylation (14 >99% ee) [51] and hydroboration (>94% ee) [52] of olefins, allylic amination (99 % ee) [53], Suzuki cross coupling reactions (Section 2.11) [54], and enamide hydrogenation (>99% ee) [55]. 

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