Synthesis, properties, and reactions of enantiomerically pure, chiral fluorous phosphines of the formula (menthyl)P(CH 2CH 2(CF 2) n−1 CF 3) 2 ( n=6, 8)

Abstract

Reactions of (menthyl)PH 2 and H 2CCHR f6 (menthyl=1 R,3 R,4 S; R f n =(CF 2) n−1 CF 3) or H 2CCHR f8 (AIBN, refluxing THF) give (menthyl)PH(CH 2CH 2R f n ) and then (menthyl)P(CH 2CH 2R f n ) 2 ( n=6, 7; n=8, 8), but with purification or other difficulties at each stage. Reactions of (menthyl)PCl 2 with IMgCH 2CH 2R f n give, under careful conditions, analytically pure 7 or 8 in 28–32% yields after distillation. Some R f n (CH 2) 4R f n also form. These represent the first chiral (and non-racemic) fluorous phosphines. Reactions of 7 or 8 with [Ir(COD)Cl] 2 and CO give trans-[(menthyl)P(CH 2CH 2R f n ) 2] 2Ir(Cl)(CO) ( n=6, 71%; 8, 51%) as analytically pure yellow oils. Their IR ν CO values show the donor/acceptor properties of 7 and 8 to be intermediate between those of P((CH 2) 3R f8) 3 and P((CH 2) 4R f8) 3. The CF 3C 6F 11:toluene partition coefficients of 7 and 8 (27°C, 78.4:21.6 and 93.7:6.3) are distinctly lower than those of P((CH 2) 2R f n ) 3 ( n=6, 98.8:1.2; n=8, >99.7:<0.3), reflecting the replacement of a linear C 8–C 10 group that is ca. 75–80% fluorinated by a cyclic C 10 terpenyl group. Reactions of 7 or 8 with [Rh(COD)Cl] 2 give [(menthyl)P(CH 2CH 2R f n ) 2]Rh(Cl)(COD) ( n=6, 69%; 8, 70%) as orange crystallizable oils.