Electronic Differences between Coordinating Functionalities of Chiral Phosphine−Phosphites and Effects in Catalytic Enantioselective Hydrogenation

Abstract

A convenient synthesis of new chiral phosphine-phosphites (P-OP) has been described. The versatility of the synthetic protocol developed has allowed the preparation of ligands with different phosphine fragments and the choice of the stereogenic element location. Analyses of the values of 1 J PSe of the corresponding diselenides are in accord with the expected lower σ-donor ability of the phosphite fragment, with respect to the phosphine group, and with an increase of phosphine basicity after substitution of phenyl substituents by methyl groups. Inspection of υ(CO) values on a series of complexes RhCl(CO)(P-OP) demonstrated a variable π-aceptor ability of the phosphite group, compensating for the change of basicity of the phosphine functionality, as well as having a rather reduced electron density at the metal center compared with diphosphine analogues. The distinct nature of the phosphorus functionalities has also been evidenced in rhodium-catalyzed enantioselective hydrogenation of methyl Z-R-acetamido-cinnamate (MAC). Thus, the coordination mode of the substrate is governed by the chiral ligand, directing the olefinic bond to a cis position with respect to the phosphite group, as demonstrated by NMR studies performed with [Rh(P-OP)(MAC)] + complexes. In consequence, the phosphite group has a greater impact on the enantioselectivity of the product. However, the optical purity of the process also depends on the nature of the phosphine group, and hence, an appropriate election of both phosphorus functionalities is required for the attainment of excellent enantioselectivities (99% ee).

Selective Staudinger Modification of Proteins Containing p‐Azidophenylalanine

“…[14,15,18] Synthesis: Compound 1 was synthesized according to published procedures. [11,20] Compound 2 was prepared by the coupling reaction of 2-(diphenylphosphino)phenol (74 mg, 0.27 mmol) [21] and 5(6)-carboxyfluorescein (100 mg, 0.27 mmol) in the presence of dicyclohexylcarbodiimide (62 mg, 0.3 mmol) in anhydrous DMF (1 mL) at ambient temperature for 12 h, and purified by using preparative TLC to give a red powder (3 mg, 2 %); HRMS (ESI-TOF) for C 39 Enrichment experiment: Anti-fluorescein antibody (20 mg mL À1 , 250 mL per well) was coated in aqueous Na 2 CO 3 (0.1 M, pH 9.6) in eight wells of an immunoplate (Fisher) at 37 8C for 4 h. Wells were washed (3 , 0.9 % NaCl, 0.05 % Tween 20), blocked with BSA (0.5 %) overnight at 4 8C again, and then incubated at room temperature for 5 h with phage (100 mL) either from a ligation reaction or a control solution. After being washed, the phage was eluted from the plate with BSA-FITC conjugate (0.05 %).…”

Theoretical Studies of Asymmetric Hydroformylation Using the Rh(R,S)‐BINAPHOS Catalyst—Origin of Coordination Preferences and Stereoinduction

“…[15] In phosphane-phosphite (P À OP) ligands, the phosphane is a good s donor and the phosphite is a poorer s donor and a better p acceptor. [16] The preferred ea coordination with the phosphinite moiety in the equatorial position has been proposed by several au-A C H T U N G T R E N N U N G thors.…”

Tuning of the Structures of Chiral Phosphane‐Phosphites: Application to the Highly Enantioselective Synthesis of α‐Acyloxy Phosphonates by Catalytic Hydrogenation

“…[4] In this regard, phosphane-phosphites are appealing compounds, due to the differences in the donor abilities of their phosphorus functions, arising from the strong p-acceptor character of the phosphite group. [5] The first applications of chiral phosphane-phosphites in asymmetric catalysis, studied by Takaya and Nozaki, provided very high enantioselectivities in the hydroformylation of olefins, [6] while more recently the scope of this class of ligands has been considerably expanded and they have provided efficient catalysts for several enantioselective transformations such as hydrogenation, hydroboration or allylic substitution, among others. [7] Moreover, the production of new chiral catalysts containing phosphane and phosphite functionalities by the use of mixtures of monodentate [8] or selfassembled ligands [9] has also been studied.…”

“…We have recently synthesized a family of modularly designed phosphane-phosphites 1 and have employed them in the highly enantioselective hydrogenation of dimethyl itaconate and methyl (Z)-a-acetamidocinnamate (MAC). [5,10] Alternatively, ligands of type 2 have provided enantioselectiviAbstract: A family of new chiral phosphane-phosphites 5 has been prepared and employed in the synthesis of rhodium complexes of formulation [Rh-A C H T U N G T R E N N U N G (cod) (5)]BF 4 (7). The use of bulky phosphane or phosphite groups in the preparation of 7 avoids the formation of undesired disubstituted complexes, one of which (9 a) has been isolated and characterized.…”