(R)-(+)-(Diphenylphosphino)-2'-isopropoxy-1,1'-binaphthyl - CAS 189274-36-0

Chiral binap/pica-Ru(II) complexes (binap=(S)- or (R)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl; pica=alpha-picolylamine) catalyze both asymmetric hydrogenation (AH) of ketones using H(2) and asymmetric transfer hydrogenation (ATH) using non-tertiary alcohols under basic conditions. The AH and ATH catalytic cycles are linked by the metal-ligand bifunctional mechanism. Asymmetric reduction of pinacolone is best achieved in ethanol containing the Ru catalyst and base under an H(2) atmosphere at ambient temperature, giving the chiral alcohol in 97-98 % ee. The reaction utilizes only H(2) as a hydride source with alcohol acting as a proton source. On the other hand, asymmetric reduction of acetophenone is attained with both H(2) (ambient temperature) and 2-propanol (>60 degrees C) with relatively low enantioselectivity. The degree of contribution of the AH and ATH cycles is highly dependent on the ketone substrates, solvent, and reaction parameters (H(2) pressure, temperature, basicity, substrate concentration, H/D difference, etc.

A series of tunable G0-G3 dendritic 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP) ligands was prepared by attaching polyaryl ether dendrons onto the four phenyl rings on the P atoms. Their ruthenium complexes were employed in the asymmetric hydrogenation of β-ketoesters, α-ketoesters, and α-ketoamides to reveal the effects of dendron size on the catalytic properties. The second- and third-generation catalysts exhibited excellent enantioselectivities, which are remarkably higher than those obtained from the small molecular catalysts and the first-generation catalyst. Molecular modeling indicates that the incorporation of bulky dendritic wedges can influence the steric environments around the metal center. In addition, the ruthenium catalyst bearing a second-generation dendritic ligand could be recycled and reused seven times without any obvious decrease in enantioselectivity.

The first series of chiral phosphine-imidazole carbene ligands based on a 1,1'-binaphthyl framework were synthesized from (R)-2-amine-2'-(diphenylphosphino)-1,1'-binaphthyl (1) in a four-step pathway. After deprotonation of these phosphine-imidazolium salts with LiO(t)Bu, and subsequent complexation with [Ir(COD)Cl]2 and anion exchange with NaBArF, phosphine-carbene chelated iridium complexes (R)-6a and (R)-6b were obtained. Their structures have been characterized by NMR and X-ray diffraction analysis. The NHC-phosphine rhodium complex (R)-6c has been also obtained by a similar synthetic method. These iridium complexes have been applied to catalyze the asymmetric hydrogenation of alkenes to give the corresponding products in moderate to excellent conversion (up to 99%) and moderate enantioselectivities under mild conditions (up to 61% ee).

The oxidative addition of MeI to the Ir(I) square-planar complex IrI(CO)((R)-(+)-BINAP) where (R)-(+)-BINAP = (R)-(+)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl)) results in the formation of two diastereomers in a 2:1 ratio of the Ir(III) oxidative addition product IrI(2)(CO)(Me)((R)-(+)-BINAP) (4a and 4b) in a 85% overall yield. Upon iodide abstraction from the diastereomeric mixture with 2 equiv of AgSbF(6) in the presence of diethyl isopropylidene malonate (DIM), two diastereomers of the dicationic complex [Ir(CO)(Me)(DIM)((R)-(+)-BINAP)][SbF(6)](2) (5) are formed in a 90% yield with a ratio of 9:1. One diastereomer of the diiodide complex 4 and one diastereomer of the dicationic complex 5 have been characterized by X-ray diffraction. An anion exchange reaction of 5 with NaBAr(4)(f-) (BAr(4)(f-) = B(3,5-(CF(3))(2)C(6)H(3))(4)) affords [Ir(CO)(Me)(DIM)((R)-(+)-BINAP)][BAr(4)(f)](2) (6) in quantitative yield. Both 5 and 6 are active Lewis acid catalysts for the polarized Nazarov cyclization and the Diels-Alder reaction.