First Resolution of a Free Fluorophosphine Chiral at Phosphorus. Resolution and Reactions of Free and Coordinated (±)-Fluorophenylisopropylphosphine

The trivalent fluorophosphine (±)-PFPh(i-Pr),
(±)-1, has been prepared by halogen exchange of the
corresponding
chlorophosphine with sodium fluoride in hot sulfolane. The neat
fluorophosphine rapidly decomposes by
equilibrium redox disproportionation into
PF3Ph(i-Pr) and
(R*,R*)/(R*,S*)-Ph(i-Pr)PPPh(i-Pr),
but in benzene,
(±)-1 has considerable thermodynamic stability. The
resolution of (±)-1 was achieved by a fractional
crystallization
of the diastereomers (R,RP)- and
(R,SP)-chloro[1-[1-(dimethylamino)ethyl]-2-naphthalenyl-C,N](fluorophenylisopropylphosphine)palladium(II),
(R,RP)- and
(R,SP)-5, whereby the less
soluble (R,RP) diastereomer
selectively
crystallized in 64% yield in a typical second-order asymmetric
transformation. Optically pure (S)-(−)-1,

−210 (c 0.59, C6H6), was liberated
from (R,RP)-5 with
(R*,S*)-1,2-phenylenebis(methylphenylphosphine).
The
optically active phosphine in benzene racemizes over 6 h without
significant redox disproportionation. The
methoxyphosphine (±)-P(OMe)Ph(i-Pr),
(±)-9, was also resolved by the method of metal
complexation. Thus,
fractional crystallization of (R,RP)-
and
(R,SP)-chloro[1-[1-(dimethylamino)ethyl]-2-naphthalenyl-C,N](methoxyphenylisopropylphosphine)palladium(II),
(R,RP)- and
(R,SP)-8, followed by
liberation of the respective optically
active methoxyphosphines from the separated diastereomers with
1,2-bis(diphenylphosphino)ethane, gave
(R)-(+)- and (S)-(−)-9 of 92% and 96% ee,
respectively. The barrier to unimolecular inversion for
(±)-9 was
determined to be >82.9 ± 0.5 kJ mol-1 by
variable temperature 1H NMR spectroscopy. The
substitution of
fluoride in (R,RP)-5 by
methoxide proceeds with predominant inversion of the configuration at
phosphorus to
give (R,RP)- and
(R,SP)-8 with
(R,SP)/(R,RP)
= 1/5. The crystal structures of
(R,RP)-5 and
(R,RP)-8 have
been
determined:  (R,RP)-5
(C23H28ClFNPPd) crystallizes in the
orthorhombic space group
P212121 with
a = 9.967(2)
Å, b = 10.998(4) Å, c = 21.324(3)
Å, Z = 4, and R = 0.031;
(R,RP)-8
(C24H31ClNOPPd) crystallizes in the
space
group P212121 with
a = 10.444(3) Å, b = 12.146(3) Å,
c = 19.047(2) Å, Z = 4, and
R = 0.026.