[220224-86-2] · C38H12F20O2P2 · (MW 942.43)
(chiral C2-symmetric bidentate phosphorus ligand with p-acceptor properties; used in the synthesis of transition metal based Lewis acids)
Physical Data: mp 118 °C; [a]D +85 (c 2.26, CH2Cl2); 1H NMR (CDCl3, 400 MHz): 6.98-7.20 (10 H), 5.18 (2 H); 31P NMR (CDCl3, 162 MHz) : 87.6 (quint, 40 Hz).
Solubility: high solubility in Et2O, CH2Cl2, EtOAc, THF, acetone, CHCl3; low solubility in pentane, hexane, cyclohexane and toluene; insoluble in methanol.
Form Supplied in: white solid.
Preparative Methods:1 to a white suspension of (+)-(R,R)-hydrobenzoin2 (901 mg, 4.21 mmol) and triethylamine (1.17 mL, 8.41 mmol) in diethyl ether (20 mL), a solution of bis(pentafluorophenyl)bromophosphine3 (3.74 g, 8.41 mmol) in diethyl ether (20 mL) was added dropwise at -78 °C. A white precipitate formed immediately. The reaction mixture was allowed to warm to ambient temperature overnight. After filtration over Celite, the solvent was removed in vacuo to give (R,R)-BIPHOP-F (3.90 g, 98%). Further purification can be achieved by recrystallization. Both enantiomers are available.
Purification: recrystallization from pentane.
Handling, Storage, and Precautions: air stable for months at room temperature (no oxidation observed).
Ligands with the electron-poor pentafluorophenyl groups have good p-acceptor properties and electronically bridge the gap between phosphites and carbon monoxide. Other diols, with4 or without5 C2-symmetry, have been used as ligand backbones. Pentafluorophenyl can also be replaced by other aromatic electron-withdrawing groups.6
BIPHOP-F is used in the synthesis of chiral transition metal Lewis acids. Because of its electronic properties, it enhances the acidity of the metal. Coordination of the bidentate ligand to the metal is accomplished by CO substitution (
The complexes are isolated, characterized and used as chiral Lewis acids. Dissociation of the labile ligand liberates a single coordination site at the metal center. These Lewis acids catalyze enantioselective Diels-Alder reactions.1,7,8 For instance, reaction of methacrolein with cyclopentadiene in the presence of the cationic iron complex (L = acrolein) occurs with exo selectivity and an enantiomeric excess of the same order of magnitude as those obtained with the successful boron and copper catalysts (
The chiral environment around the coordination site of the catalyst is created by the perfluoroaryldiphosphinite ligand (crystallographic data).