Efficient synthesis of (R)- and (S)-(6,6'-difluorobiphenyl-2,2'-diyl) bis(diphenylphosphine); Electron-poor biphenyl-type ligands for transition metal catalysts

Article abstract of DOI:10.1016/0957-4166(94)80172-X

Racemic title compound (RS)-5 is synthesized (Scheme 1, 100g scale) in four simple steps (49% overall yield) from meta-fluorobromobenzene 1. (RS)-5 is efficiently resolved (Scheme 2) utilizing commercial (S)-(+)-dipalladium complex 9 to give homochiral (S)-(+)-5 and (R)-(-)-5 in 75 and 95% of theoretical yield, respectively. Enantiomerically pure diphosphines (S)-5 and (R)-5 do not racemize in organic solutions, even when heated to 207°C. Homochiral palladium(II) dichloride complexes (-)-11 and (+)-11 are prepared in quantitative yield. In situ rhodium(I)-complex of homochiral 5 is an efficient catalyst for alkene - hydroboration by catecholborane and requires high hydrogen pressure to catalyze hydrogenation. Interesting anomalies of the specific rotation are observed for homochiral diphosphines (S)-(+)-5 and (R)-(-)-5. The specific rotation [α](D)²⁵ of (S)-(+)-5 measured in similar aromatic hydrocarbons (toluene, o-xylene, mesitylene, tetralin) varies from +114.9 (c 0.99, toluene) to -73.9 (c 0.46, tetralin).