Palladium‐catalyzed Asymmetric Hydrosilylation of Styrene and Its Derivatives with Chiral Phosphoramidite Ligands Containing Chiral Ferrocenyl Amine

Abstract

Asymmetric hydrosilylation was one of the most effective methods, which provided optically active organosilanes as a synthetically useful intermediate in organic synthesis. 1 One useful transformation is the Tamao-Fleming oxidation, which is an oxidation reaction of carbon silicone bond to afford optically active alcohols with retention of configuration. 2 Palladium-monophosphorus ligand complex is the wellknown catalysts in asymmetric hydrosilylation of olefins. Among various types of monophosphines, the monodentate phosphine (MOP)-type ligands were known as a highly reactive and enantioselective ligands. 3 Ferrocene-based monophosphine ligands such as L1 were also highly effective ligands in asymmetric hydrosilylation of olefins ( Figure 1). 4 Recently, chiral phosphoramidite ligands which were easily prepared from readily available compounds with a good stability 5 were applied to asymmetric hydrosilylation of styrene and its derivatives. 6 As well as the Feringa ligand (L2), 6a phosphoramidites which had 1,1 0spirobiindane backbone 6b or BINOL backbone with unsymmetric secondary amines 6c demonstrated that these ligands were highly efficient for the Pd-catalyzed asymmetric hydrosilylation of styrenes. Chiral phosphoramidite ligands (L3a) derived from bis((R)-1-ferrocenylethyl)amine, introduced by Zheng and co-workers, were used in the Cucatalyzed asymmetric 1,4-conjugate addition. 7 Thus, we attempted to prepare whole diastereomers of the ferrocenyl amines and to prepare all the phosphoramidite ligands from (S)-BINOL and these diastereomeric ferrocenyl amines in order to evaluate their utility in asymmetric hydrosilylation of styrenes as a chiral ligand, focusing on the effect of the diastereomeric ferrocenyl amino group on the ligands in their enantioselectivity. In this context, we synthesized all the diastereomeric phosphoramidites from (S)-BINOL and diastereomeric bis(1-ferrocenylethyl)amines. Two racemic (R,R)and (S,S)-4 and one meso (R,S)-4 were obtained by the substitution reaction between the appropriate ammonium salt 2 and the primary amine 3, respectively, starting from each of enantiomerically pure N,N-dimethylaminoethylferrocene (1). 7,8 Diastereomeric phosphoramidite ligands L3 were easily prepared from (S)-BINOL, bis(1-ferrocenylethyl)amines 4, and PCl 3 in the presence of trimethylamine (Scheme 1).With these phosphoramidite ligands in hands, we examined the reactivity and enantioselectivity of the hydrosilylation of styrene (5a) using these diastereomeric ferrocenyl phosphoramidite ligands ( Table 1). The catalytic reactions were performed without solvent with 1.0 mol % of palladium catalysts generated in situ by mixing [PdCl(π-C 3 H 5 )] 2 and L3 (Pd/P = 1/2). The reactions proceeded smoothly at 20 C in 20 h to give optically active 1-phenyl-1-(trichlorosilyl)ethane (6a). After Tamao-Fleming oxidation, enantioselectivities of the hydrosilylation were deduced from enantiomeric excess of 1-phenylethan-1-ol (7a). It was found that (S a ,R c ,R c ,)-L3a, which had the same absolute configuration...

Palladium‐Catalyzed Enantioselective Hydrofunctionalization of Alkenes: Recent Advances

“…In 2012, Lemaire and coworkers synthesized P-chirogenic monodentate binaphthyl phosphines (L7) from enantiopure BINOL in five steps, which was successfully applied to palladium-catalyzed asymmetric hydrosilylation of styrene with trichlorosilane. [42] Subsequently, Higham et al [43] Han et al [44] and Panossian et al [45] designed and synthesized chiral MOPphosphonite ligand (L8), phosphoramidite ligand (L9), atropoenantiopure monodentate biphenylphosphine ligand (L10), respectively, for the enantioselective hydrosilylation of styrenes with trichlorosilane (Scheme 9).…”

Thermal and thermo-oxidative stability of a series of palladium and platinum ferrocenylamine sulfides and selenides

“…Ferrocenylamines possess rich chemistry and a wide range of applications because of their electron-rich aromatic nature, the nucleophilicity of the amino group, their high electrochemical potential, and their unique stereostructure as sandwich-like compounds. 1,2 Many ferrocenylamine derivatives have been synthesized and frequently incorporate metals, for example, palladium, 3–5 platinum, 6 copper, 7 bismuth, 8 silver, 9 gold, 9,10 and rhodium. 11 Their complexes are widely used as catalysts in various organic reactions for example, selective hydrogenation, 12–15 cross–coupling reactions, 12,16,17 and for the synthesis of ferrocene-fused heterocycles.…”

“…11 Their complexes are widely used as catalysts in various organic reactions for example, selective hydrogenation, 12–15 cross–coupling reactions, 12,16,17 and for the synthesis of ferrocene-fused heterocycles. 18 The special structure of chiral ferrocenylamines is useful in stereoselectivity, for example, asymmetric hydrogenation, 19 hydrosilylation, 3,5 aldol reactions, 20 cycloaddition, 10 allylic alkylation, 7 C–H arylation, 4 and double C–H functionalization, 21 as well as for electrochemical enantiodifferentiation. 22 Industrial applications involve production of redox–active anion sensors, 23 supercapacitor electrodes, 24 corrosion inhibitors, 25 and electro- and photo-responsive materials.…”