Palladium catalysts, hydrosilylation using

The most active palladium catalyst system developed for the asymmetric hydrosilylation of cyclopentadiene (Scheme 23) involves the use of the (/ )-MOP-phen ligand (38), which shows significant enhancement of enantioselectivity compared to (R)-MeO-MOP (80% ee from (38), 39% ee from (36a)).114 Other phosphine ligands that afford active palladium catalysts for the same transformation include the /3-7V-sulfonylaminoalkylphosphine (39) and phosphetane ligand (40) (Equation (13)).115-117 A comparison of the enantioselectivities of these ligands for the palladium-catalyzed hydrosilylation of cyclopentadiene is given in Table 8. 

Widenhoefer has also disclosed an interesting extension consisting of hydrosilylative cyclization of a diene catalyzed by palladium. High enantioselectivity (up to 95% ee) was achieved by using palladium catalysts with Ci-symmetric pyridine-oxazoline ligands351,364 and recent mechanistic studies have confirmed the involvement of an intramolecular carbometallation step.365... 

In the asymmetric hydrosilylation of 1,3-cyclohexadiene 38 (Scheme 10, Table 4), catalyzed by chiral ferrocenylphosphines 5 and 40, the enantioselectivity is higher with phenyldifluorosilane than that with trichlorosilane or methyldichlorosilane (entries 1—4). The reaction of 38 with phenyldifluorosilane in the presence of a palladium catalyst coordinated with ferrocenylphosphine 40b gave allylsilane (A)-39c with 77% ee.58,59 The use of (j3-N-sulfonylaminoalkyl (phosphine 35a for the reaction of 38 with methyldichlorosilane exhibited the same level of asymmetric induction (entries 5-6).53 In this asymmetric hydrosilylation, combination of trichlorosilane and... 

Hydrosilylation of alkyl-substituted 1,3-dienes 46g-46j in the presence of a ferrocenylmonophosphine-palladium catalyst also proceeded with high regioselectivity to give the corresponding 1,4-addition products with moderate enantioselectivity (entries 13-16).52 62 Enantioselectivity was improved by using ligands 37f and 37g (entries 17 and 18).57a... 

A new type of asymmetric hydrosilylation which produces axially chiral allenylsilanes has been reported by use of a palladium catalyst coordinated with the bisPPFOMe ligand 51b.64 The hydrosilylation of l-buten-3-ynes substituted with bulky groups such as tert-butyl at the acetylene terminus took place in a 1,4-fashion to give allenyl(trichloro)-silanes with high selectivity. The highest enantioselectivity (90% ee) was observed in the reaction of 5,5-dimethyl-T hexen-3-yne with trichlorosilane catalyzed by the bisPPFOMe-palladium complex (Scheme 13). 

Recently, much better results have been obtained using the palladium catalyst D [with ( + )-(/ )-MOP], Hydrosilylation of norbomene with trichlorosilane in the presence of this catalyst gives a quantitative yield of e.vo-2-trichlorosilylbornane which upon oxidation produces (l.S .2.S.4f )- .w-2-norbornanol (25) with 96% ee30. 

Asymmetric allylation using optically active allylic siliconates has been reported [96]. The allylic siliconates were prepared by asymmetric hydrosilylation of 1,3-dienes and HSiCla catalyzed by a chiral palladium catalyst followed by ethanolysis. Complete asymmetric induction of allylic siliconates to homoallylalcohols was accomplished (Sch. 55). 

Hydrosilylation of monosubstituted alkenes with palladium catalysts and trichlorosilane follows a course which favors branched products. By using a chiral phosphine ligand, asymmetric reaction is feasible. Initially, menthyldiphenylphosphine (MDPP, 93) and neomenthyldiphenylphosphine (NMDPP, 94) were employed with little success. Later, (/ )-/VA -dimethyl-l-[(S)-2-diphenylphosphinoferroce-nyl]ethylamine [(R)-(S)-PPFA] (95) and its enantiomer were prepared, and these have proved to be the... 

Optically active alcohols, amines, and alkanes can be prepared by the metal catalyzed asymmetric hydrosilylation of ketones, imines, and olefins [77,94,95]. Several catalytic systems have been successfully demonstrated, such as the asymmetric silylation of aryl ketones with rhodium and Pybox ligands however, there are no industrial processes that use asymmetric hydrosilylation. The asymmetric hydrosilyation of olefins to alkylsilanes (and the corresponding alcohol) can be accomplished with palladium catalysts that contain chiral monophosphines with high enantioselectivities (up to 96% ee) and reasonably good turnovers (S/C = 1000) [96]. Unfortunately, high enantioselectivities are only limited to the asymmetric hydrosilylation of styrene derivatives [97]. Hydrosilylation of simple terminal olefins with palladium catalysts that contain the monophosphine, MeO-MOP (67), can be obtained with enantioselectivities in the range of 94-97% ee and regioselectivities of the branched to normal of the products of 66/43 to 94/ 6 (Scheme 26) [98.99]. 

Asymmetric synthesis through a selective monofunctionalization of enantiotop-ic positions is considered as being one of the most attractive strategies for the one-step construction of multiple chiral carbon centers [34,35]. Asymmetric hydrosilylation of norbornene (21) was first attempted by use of a palladium catalyst coordinated with ferrocenylmonophosphine, (1 )-(S)-PPFA (15a) [28]. The... 

Palladium-catalyzed hydrosilylation of 1,3-dienes is one of the important synthetic methods for allylic silanes, and considerable attention has been directed to the asymmetric synthesis of the latter by catalytic methods [9]. Optically active allyhc silanes have been used as chiral allylating reagents in S reactions with electrophiles, typically aldehydes [38,39]. In the presence of Pd catalysts the reaction with hydrosilanes containing electron-withdrawing atoms or substituents on sihcon usually proceeds in a 1,4-fashion giving allyHc silanes [40,41]. Asymmetric hydrosilylation of cyclopentadiene (29) forming optically active 3-silylcyclopentene (30) has been most extensively studied (Scheme 13). In the first report, hydrosilylation of cyclopentadiene (29) with methyldichlorosilane in the presence of 0.01 mol % of palladium-(l )-(S)-PPFA (15a) as a catalyst gave... 

Polymer-anchored catalysts are used for the hydrosilylation of butadiene, giving cis-but-2-enylsilanes in excellent yield . Palladium complexes on inorganic supports are comparable or even more effective than their soluble analogues such as Pd(PhCN)2Cl2 and Pd(PPh3)2Cl2. However, these catalysts are not stable to reuse. 

The hydrosilylation of isoprene with palladium catalysts using chlorohydrosilanes affords only 1 1 adducts. Trimethylsilane does not add to isoprene at all. In most cases, the reaction gives 2-methyl-2-butenylsilane exclusively in excellent yield (equation 38)90,91, but at a higher temperature the formation of a small amount of 3-methyl-2-butenylsilane is detected89. 

One of the most common methods for the preparation of enantiomerically enriched organosilanes is by palladium-catalysed asymmetric hydrosilylation of alkenes in the presence of trichlorosilane. This area has been dominated by the use of monodentate phosphorus-based ligands and, in particular, Hayashi s MOP ligand/palladium catalyst combination offers a high level of enantioselectivity. The MOP ligands include MeO-MOP (2.139), H-MOP ligands such as (2.140) ... 

In 1993 Uozumi et al. reported on the regio- and enantioselective hydrosilylation of styrene derivatives using an optically active palladium catalyst [1]. In the context of these examinations the authors also mentioned the reaction of indene with trichlorosilane in all cases the 1-substituted products only were got no further characterization was given, however. In accordance with these results, our investigations on the hydrosilylation of indene with trichlorosilane, chlorodimethyl-silane, and dichloromethylsilane in the presence of Speier s catalyst showed the same addition tendencies by distillation we isolated in high yields trichloro(l-indanyl)silane (la), dichloro(l-in-danyl)methylsilane (lb), and chloro(l-indanyl)dimethylsilane (Ic), respectively (Scheme 1). 

Palladium complexes also catalyze hydrosilylation, and particular emphasis has been placed on the use palladium catalysts for asymmetric hydrosilylation. The most selective of these catalysts contains a binaphthyl monophosphine ligand. - Finally, lanthanides have also been used for hydrosilylation. Lanthanide-metallocene catalysts can be highly active for the hydrosilylation of olefins, and lanthanides bearing chiral ligands catalyze asymmetric hydrosilylation with measurable enantiomeric excess. ... 

As noted earlier in this chapter, the enantioselective hydrosilylation of olefins could be a useful method to prepare chiral, non-racemic alcohols. A.lthough the scope of highly enantioselective hydrosilylations is limited, high enantioselectivities have been obtained for the asymmetric hydrosilylation of alkenes and vinylarenes. A majority of the most selective chemistry has been conducted using a palladium catalyst containing an axially chiral monophosphine ligand. 

Asymmetric hydrosilylation of alkenes, catalysed by ferrocenylphosphine-palladium complexes, can be utilized in a synthesis of optically active alcohols from alkenes (Scheme 1). The initial optically active silane adducts are converted to alkyl pentafluorosilicates (1) which are then cleaved oxidatively, with retention of configuration, using peracid (c/. 3,132). Complex (2) was the best of several hydrosilylation catalysts examined using this, alcohols with enantiomeric purities of approx. 50% were obtained from norbornene and styrene as the alkenes. 

The syntheses of axially chiral biarylphosphine oxides based on alkynylphosphine oxide 2.157 and acetylene was carried out using chiral cobalt catalyst 2.159 [100, 105, 106]. The [24-24-2] cycloaddition, however, resulted in axially chiral biarylphosphine oxides 2.160 with moderate yield and enantioselectivity (Scheme 2.55). It was accompanied by a recovery of some of the corresponding phosphines. The newly obtained phosphines were used in the reaction of palladium-catalyzed hydrosilylation of unsymmetrical alkenes [100]. 

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