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

Abstract

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 PF(3)Ph(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,R(P))- and (R,S(P))-chloro[1-[1-(dimethylamino)ethyl]-2-naphthalenyl-C,N](fluorophenylisopropylphosphine)palladium(II), (R,R(P))- and (R,S(P))-5, whereby the less soluble (R,R(P)) diastereomer selectively crystallized in 64% yield in a typical second-order asymmetric transformation. Optically pure (S)-(-)-1, -210 (c 0.59, C(6)H(6)), was liberated from (R,R(P))-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,R(P))- and (R,S(P))-chloro[1-[1-(dimethylamino)ethyl]-2-naphthalenyl-C,N](methoxyphenylisopropylphosphine)palladium(II), (R,R(P))- and (R,S(P))-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 (1)H NMR spectroscopy. The substitution of fluoride in (R,R(P))-5 by methoxide proceeds with predominant inversion of the configuration at phosphorus to give (R,R(P))- and (R,S(P))-8 with (R,S(P))/(R,R(P)) = (1)/(5). The crystal structures of (R,R(P))-5 and (R,R(P))-8 have been determined: (R,R(P))-5 (C(23)H(28)ClFNPPd) crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 9.967(2) Å, b = 10.998(4) Å, c = 21.324(3) Å, Z = 4, and R = 0.031; (R,R(P))-8 (C(24)H(31)ClNOPPd) crystallizes in the space group P2(1)2(1)2(1) with a = 10.444(3) Å, b = 12.146(3) Å, c = 19.047(2) Å, Z = 4, and R = 0.026.

Resolution of β-aminophosphines with chiral cyclopalladated complexes

“…The bond lengths within the ortho-metallated benzylamine chelate (see Table 2) are quite similar to those found in similar palladium complexes containing other tertiary phosphines [19,26].…”

“…1) shows the j 1 -P-coordination by the aminophosphine ligand L 1 . The geometry around the palladium metal center is slightly distorted square planar, with a trans arrangement of the nitrogen atom from the benzylamine moiety and the phosphorus atom, similar to what was already observed in [PdCl{PPh-( i Pr)(OMe)}(C,N)] with C,N = (R)-{(1-(dimethylamino)ethyl}-2-naphtalenyl) [26].…”

“…According to the literature [23,26], the enantiomerically enriched phosphine ligand can be released from the cyclopalladated complex by addition of one equivalent of chelating bis(diphenylphosphino)ethane (dppe) ligand and easily isolated by extraction with flash chromatography. Although the ligand can then be coordinated to any transition metal, the ortho-palladium complex can not be recovered.…”

Our Odyssey with Functionalized Chiral Phosphines: From Optical Resolution to Asymmetric Synthesis to Catalysis

“…Since the 1980s, Wild and co‐workers have researched intensively on the resolution of dissymmetric organic compounds bearing phosphorus and/or arsenic atom(s) . Through their studies, it was found that the μ‐bischloro‐(1‐naphthyl)dimethylamine palladacycle 1 performed exceedingly well as a resolving agent, surpassing its benzylamine predecessor 2 .…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 19, 2008) and the discipline

“…Centrosymmetric statistics were obtained for the X-ray data for all of the crystals. A chiral fluorophosphine, C 6 H 5 P(i-C 3 H 7 )F, has been shown to readily decompose into the related fluorophosphorane, C 6 H 5 P(i-C 3 H 7 )F 3 , and diphosphine [C 6 H 5 P(i-C 3 H 7 )] 2 , the latter with loss of stereointegrity at one phosphorus [281]. Does it follow that the two diasteromeric diphosphines products have very nearly the same Gibbs free energy and presumably comparable enthalpies of formation?…”