Metal controlled enantioselectivity in the catalytic asymmetric hydrosilylation

Synthesis of Optically Active Organoantimony Compounds Having an (S)-.ALPHA.-Methylbenzyldimethylamine Group and Its Evaluation for Asymmetric Reaction.

“…Consequently, the best result was obtained when the reaction was carried out in the presence of [RhCl(COD)] 2 and the ligand 4 (1 : 1) in THF at 0°C, although the enantioselectivity was relatively low (18% ee) (Entry 3). The enantioselectivity of the reaction demonstrated here is comparable with those observed for the same reactions in the presence of phosphine ligand AMPhos (27-51% ee) [14][15][16][17] or its arsenic congener AMArs (0% ee). 17) In order to clarify the ability of the ligand 4 for enantioselective hydrosilylation, we attempted the reaction of the other ketones 5b-d.…”

“…1) A number of chiral ligands containing nitrogen, 2) phosphorus [3][4][5][6][7][8][9] and arsenic [10][11][12][13] have been widely studied and are well documented. With respect to enantiomerically pure phosphine ligands bearing a chiral benzylamine moiety, (R/S)-[a-methyl-2-(diphenylphosphino)-benzyl]dimethylamine (AMPhos) [14][15][16][17] and its (h 6 -arene)-chromium complex 18,19) have been reported to be effective chiral ligands for enantioselective reductions, cross-coupling reactions, and allylic alkylations. It is also known that a variety of optically active phosphine derivatives bearing a ferrocene skeleton can be used in a wide range of asymmetric reactions.…”

Asymmetric hydrosilylation, transfer hydrogenation and hydrogenation of ketones catalyzed by iridium complexes

“…Kreuzfeld and co-workers used another P,N ligand, named amphos 1 (Scheme 2), in the hydrosilylation of acetophenone by diphenylsilane [13]. Good conversions could be obtained, but with low e.e., lower than with the corresponding rhodium systems with the same ligand (up to 50% and with opposite absolute configuration).…”

“…One interesting aspect is the reversal of enantioselectivity on going from Rh to Ir, observed experimentally in several cases [13][14][15][16]. Moberg has observed an increase of enantioselectivity, the extent of which depends on the nature of the anion, upon the addition of silver salts to the [MCl(COD)] 2 /L* precatalyst (M = Rh, Ir) (Scheme 7).…”

Toggling enantioselective catalysis—a promising paradigm in the development of more efficient and versatile enantioselective synthetic methodologies

“…One of the first examples of "inverse strategy" adopted to tackle the refinement of an asymmetric catalytic synthetical methodology was reported by Kreuzfeld. 5 This author chose one chiral ligand, (S)-amphos 1, and tested it with several metals in the asymmetric hydrosilylation of acetophenone 2 (Scheme 1), instead of the common practice to screen a variety of ligands against a metal. Cyclooctadienerhodium(I) in combination with (S)-amphos gave the (S)-benzylic alcohol 3 in high conversion, whereas iridium, platinum and palladium induced prevalent formation of the (R) enantiomer.…”