Ligand MOPS,

The MOP range of ligands designed by Hayashi has proved remarkably useful for asymmetric hydrosilylation reactions.59 MOP ligands are a series of enantiomerically pure monophosphine ligands whose chirality is due to 1,1 -binaphthyl axial chirality. 

However, in the palladium-catalyzed addition of HSiCl3 to -substituted styrenes, the size of the substituent on the MOP ligand is crucial. While (R)-MeO-MOP/[Pd(//3-C3H5)Cl]2 yielded (R)-phenylethanol with poor enantioselectivity (14% ee),110 replacement of the methoxy group with hydrogen (H-MOP, (36d)) affords the same product with 93% ee (Equation (ll)) 111... 

The palladium-catalyzed asymmetric hydrosilylation of styrenes has been applied to the catalytic asymmetric synthesis of l-aryl-l,2-diols from arylacetylenes (Scheme 6).46 Thus, ( )-l-aryl-2-(trichlorosilyl)ethenes, which are readily generated by platinum-catalyzed hydrosilylation of arylacetylenes, were treated with trichlorosilane and the palladium catalyst coordinated with MOP ligand 12f to give 1 -aryl-1,2-bis(silyl)ethanes, oxidation of which produced the enantiomerically enriched (95-98% ee) 1,2-diols. 

Linear 1,3-dienes have also been subjected to the palladium-catalyzed asymmetric hydrosilylation (Scheme 12, Table 5). Reaction of 1-phenyl-l,3-butadiene 46a with HSiClj catalyzed by palladium-(/ )-(A)-PPFA 5a gave a mixture of regioisomeric allysilanes 47, and 48 and 49, in a ratio of 94 to 6, the major isomer 47 and the minor isomer 48 being 64% ee (S) and 30% ee (R), respectively (entry l).60 7r-Allylpalladium intermediate 50 was proposed for this hydrosilylation. Use of phenyldifluorosilane in place of trichlorosilane slightly improved the enantioselectivity (entry 8).58,61 Similar level of enantioselectivity (71-72% ee) was reported for the reaction using Ar-MOP ligand 37f (entry 11) and its dioctylated derivative 37g (entry 12).57a... 

Also norbomene and related systems, as well as dihydrofuranes, have been hydrosilated with good enantioselectivities with similar MOP ligands. Intramolecular rhodium catalyzed asymmetric hydrosUations have been achieved with good enantioselectivities, for example with meso- or other allylsilylethers. ... 

In contrast to the formation of linear achiral allylation product on usage of the catalytic system with dppe ligand, employment of the (P)-MeO-MOP ligand gave the branched product in a high regiochemistry and high enantioselectivity. 

In the last decade there have been remarkable advances in the syntheses and applications of optically active a-chiral allylsilanes. Asymmetric hydrosilylation of 1,3-dienes provides convenient access to these allylsilanes [387]. Hayashi et al. have demonstrated tliat axially chiral monophosphines (MOP) are efficient chiral ligands in the Pd-catalyzed asymmetric hydrosilylation [388]. In particular, the MOP ligand 124 can realize high catalytic activity and enantioselectivity in the reaction of cyclic 1,3-dienes with HSiCL (Scheme 10.137) [388a,b]. The allyltrichlorosilanes obtained are quite valuable for highly diastereo- and enantioselective allylation of aldehydes by Kobayashi s procedure [371]. 

An amphiphilic polystyrene-poly(ethylene glycol) (PS-PEG) resin-support has been used successfully as a suitable support for asymmetric catalysts in aqueous media. A polymeric (R]-2-(diphenylphosphino) binaphthyl (MOP) ligand 205 anchored onto the PS-PEG resin was shown to be an effective chiral ligand for the enantioselective p-allyhc substitution under aqueous condihons (Scheme 3.67) [130]. 

The axially chiral, monophosphine ligand, MeO-MOP (7a), was not as effective for styrene derivatives as for simple terminal olefins [31]. The palladium-catalyzed hydrosilylation of styrene (13) with trichlorosilane in the presence of the (H)-MeO-MOP ligand (7a) under standard conditions (without solvent) followed by oxidation gave (H)-l-phenylethanol (16) with only 14% ee (Scheme 8). Use of benzene as solvent for the hydrosilylation reaction improved the enanti-... 

The asymmetric hydrosilylation of 1-alkenes giving highly optically active 2-tri-chlorosilylalkanes is catalyzed by palladium complexes with chiral monodentate binaphthyl phosphine (MOP) ligands. ... 

Subsequent to this, the 6- and 6 -anchored PS-PEG MOP ligands 140 and 141 have been prepared and the catalytic activity in asymmetric tr-allylic reduction of their corresponding allylpalladium complexes compared and contrasted. The 6-anchored ligand was found to be the best and the 6 -analog the worst. This has been attributed to the fact that the 6 -position on a MOP ligand is in close proximity with the substrate moiety and thus the effect of attaching a sterically demanding tether at this position may well be to reduce catalytic activity. 

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