Synthesis, properties, and reactions of enantiomerically pure, chiral fluorous phosphines of the formula (menthyl)P(CH2CH2(CF2)(n-1)CF3)(2) (n=6, 8)
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Reactions of (menthyl)PH2 and H2C=CHR(f6) (menthyl=1R,3R,4S; R(fn)=(CF2)(n-1)CF3) or H2C=CHR(f8) (AIBN, refluxing THF) give (menthyl)PH(CH2CH2R(fn)) and then (menthyl)P(CH2CH2R(fn))2 (n=6, 7; n=8, 8), but with purification or other difficulties at each stage. Reactions of (menthyl)PCl2 with IMgCH2CH2R(fn) give, under careful conditions, analytically pure 7 or 8 in 28-32% yields after distillation. Some R(fn)(CH2)4R(fn) 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(CH2CH2R(fn))2]2Ir(Cl)(CO) (n=6, 71%; 8, 51%) as analytically pure yellow oils. Their IR (CO) values show the donor/acceptor properties of 7 and 8 to be intermediate between those of P((CH2)3R(f8))3 and P((CH2)4R(f8))3. The CF3C6F11:toluene partition coefficients of 7 and 8 (27C, 78.4:21.6 and 93.7:6.3) are distinctly lower than those of P((CH2)2R(fn))3 (n=6, 98.8:1.2; n=8, >99.7:<0.3), reflecting the replacement of a linear C8-C10 group that is ca. 75-80% fluorinated by a cyclic C10 terpenyl group. Reactions of 7 or 8 with [Rh(COD)Cl]2 give [(menthyl)P(CH2CH2R(fn))2]Rh(Cl)(COD) (n=6, 69%; 8, 70%) as orange crystallizable oils.