Chiral Palladium Template Promoted Asymmetric Hydrophosphination Reaction between Diphenylphosphine and Vinylphosphines

Abstract

An organopalladium complex containing ortho-metalated (S)-(1-(dimethylamino)ethyl)naphthalene as the chiral auxiliary has been used to promote the asymmetric hydrophosphination reactions between diphenylphosphine and (E)- or (Z)-diphenyl-1-propenylphosphine in high regio- and stereoselectivities under mild conditions. Hydrophosphination of (Z)-diphenyl-1-propenylphosphine with diphenylphosphine gave (S)-(-)-prophos as the major product. Using the same chiral metal template, the corresponding hydrophosphination reaction with (E)-diphenyl-1-propenylphosphine gave (R)-(+)-prophos predominantly. The hydrophosphination reactions generated the asymmetric diphosphines as bidentate chelates on the chiral naphthylamine palladium templates. The template products obtained undergo cis-trans isomerization in solution to form an equilibrium mixture of regioisomers. X-ray analysis of the major template products obtained from the hydrophosphination of (Z)-diphenyl-1-propenylphosphine reveals that the two regioisomers are cocrystallized in a 1:1 ratio. The naphthylamine auxiliary could be removed chemoselectively from the template products by treatment with concentrated hydrochloric acid to form the corresponding optically pure neutral complexes [(R)- or (S)-(prophos)PdCl(2)]. Subsequently, the (R)- and (S)-dichloro complexes undergo ligand displacement with aqueous cyanide to generate the corresponding optically pure diphosphine ligands in high yields. Mechanistic pathways explaining the stereoselectivity of the chiral organopalladium template promoted hydrophosphination reactions are also proposed.

Asymmetric hydroarsination reactions toward synthesis of alcohol functionalised C-chiral As–P ligands promoted by chiral cyclometallated complexes

“…The monodentate 3-diphenylphosphanyl-but-3-en-1-ol was coordinated to the palladium complex (Rc)-1 via a regiospecific bridge splitting process (Scheme 1) [7]. It is known that the chloro ligand in the template complex (Rc)-2a is kinetically and thermodynamically stable and is not readily displaced by incoming monodentate arsine ligands [8].…”

“…The 31 P NMR spectrum showed a singlet at d 77.6 indicating that only one diastereomer was generated out of the two possible diastereomers. Unlike the addition of the analogous secondary phosphine which resulted in cis-trans regioisomers of the products [7,9], introduction of diphenylarsine in this reaction is regiospecific. The P atom occupies the coordination site trans to the N atom of the chiral auxiliary.…”

Novel Enantioselective Synthesis of Functionalized Pyridylarsanes by a Chiral Palladium Template Promoted Asymmetric Hydroarsanation Reaction

“…While the addition of the secondary phosphane to vinylic phosphanes resulted in cis/trans regioisomeric products, [12] the addition of diphenylarsane to vinylic pyridines is 100 % regioselective, wherein the As atom occupies the coordination site trans to the N atom. The high regioselectivity observed in the present case is in agreement with what has been observed for similar N-P heterobidentate ligands.…”

“…The recoordination process is also a means of verifying the op-tical purity of the released ligand to establish the identity of the minor isomers that were generated in the original hydroarsanation reaction. [16,12] The recoordination procedure was monitored by 1 H NMR spectroscopy. In CDCl 3 , the 1 H NMR spectrum of the recoordination product showed only one product, thus confirming that the liberated (R)-5 is optically pure.…”

Asymmetric [2+2] Cycloaddition of (E)‐2‐(Diphenylphosphanyl)styrene Promoted by a Chiral Metal Template

“…Recomplexation of the liberated diphosphane to the (R)-form of the platinum template, followed by fractional crystallization, allows separation of the optically pure platinum template complex containing the diphosphane ligand (1R,2R,3R,4R)-1,2-bis(diphenylphosphanyl)-3,4-diphenylcyclobutane, from which the free diphosphane can be subsequently liberated efficiently. rearrangements, [10] reaction promoters for the oxidative coupling between vinylphosphanes and imines, [11] chiral templates for asymmetric Diels-Alder reactions, [12] asymmetric hydroamination, [13] and hydrophosphanylation [14] reactions. In pursing our interest in the application of chiral cyclometalated-amine complexes in asymmetric transformations, we present here the organoplatinum-promoted asymmetric [2+2] dimerization of (E)-2-(diphenylphosphanyl)styrene.…”