S. Selvaratnam

NMR assignment of absolute configuration of a P-chiral diphosphine and mechanics of its stereoselective formation

Abstract Two-dimensional rotating-frame nuclear Overhauser enhancement (ROESY) NMR spectra are used to determine the absolute configuration of (+)-diphenyl-phosphine-2,3-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]hept-2-ene. This diphosphine ligand is obtained from the palladium complex-promoted Diels-Alder reaction between diphenylvinylphosphine and 1-phenyl-3,3-dimethylphosphole in the presence of ( R )-dimethyl(1-(α-naphthyl)ethylamine as the chiral auxiliary. The origin of the stereoselectivity in this asymmetric reaction is also revealed by solution NMR studies.

SYNTHESIS AND ABSOLUTE STEREOCHEMISTRY OF AN ORGANO-PALLADIUM COMPLEX CONTAINING A P-CHIRAL DIPHOSPHINE LIGAND

Abstract The cationic palladium(II) complex containing ortho-metallated (R)-1-[1-(dimethylamino)ethyl]benzene and (1α, 4α, 5α(S), 7R)-[5-(diphenylphosphino)-2,3-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]]-hept-2-ene was prepared by both the coordination of the diphosphine to the organopalladium unit and by the asymmetric Diels-Alder reaction between 1-phenyl-3,4-dimethylphosphole and diphenylvinylphosphine using the organopalladium unit as the reaction promoter. Compound C36H40ClNO4P2Pd (−)-2, with [α]D − 39.0 (c = 1.0, CHCl3), crystallizes in the monoclinic space group P21, with a = 10.538(4), b = 16.031(5), c = 10.709(4)A. β = 100.20(3)°, V = 1781(1) A 3 , Z = 2, D c = 1.41 gcm −3 , μ( Cu K a = 60.5 cm −1 , F(000) = 776 . The structure refinement converged to R1 = 0.033, wR2 = 0.081 for 2905 independent observed reflections [|F0| > 4σ(|F0|), 2θ ≤ 126 °] and 387 parameters. The absolute stereochemistry of the phosphorus and the three carbon stereogenic centres in the diphosphine ligand were assigned unambiguously by both an R-factor test [R+ = 0.033, R− = 0.054] and the Flack parameter [x+ = −0.02(2), x− = +1.02(2)].

Palladium(II) ion promoted hydroamination of di(phenylethynyl)phenylphosphine and aniline: a facile synthesis of a six-membered P–N heterocycle

Abstract The six-membered aromatic heterocycle 1,4-2H-1,2,4,6-tetraphenyl-1,4-azaphosphabenzene was generated efficiently via a [PdCl 2 (NCMe) 2 ] promoted hydroamination between PhP(CCPh) 2 and aniline. The heterocyclization reaction adopts a stepwise mechanism during which the unstable intermediate imino complex cis -dichloro{1,2-diphenyl-3-phenyl(phenylethynyl)phosphino-1-aza-1-propene}palladium(II) is formed. The end product of the cyclization reaction is a palladium complex in which the six-membered aromatic P–N heterocyclic ring is coordinated to the metal center as a typical monodentate ligand via phosphorus. The azaphospha heterocycle can subsequently be liberated from the palladium reaction activator as an air-stable yellow solid by treating the palladium complex with KCN. In contrast to the intermediate imino-complex, where the CN is readily hydrolyzed by HCl, the aromatic heterocycle is stable in strongly acidic environments.

Asymmetric synthesis and the novel retro Diels–Alder reaction of a P-chiral sulfonyl-substituted phosphanorbornene

Abstract An asymmetric Diels–Alder reaction between phenylvinylsulfone and 1-phenyl-3,4-dimethylphosphole in the presence of a chiral organometallic reaction promoter generates the corresponding P -chiral sulfonyl-substituted phosphanorbornene which is found to undergo the facile cycloreversion reaction under mild conditions.

Asymmetric synthesis and the coordination chemistry of a P-chiral diphosphine monoxide

The organopalladium complex containing ortho-metalated (R)-(1-(dimethylamino)ethyl)-naphthalene as the chiral auxiliary has been used successfully to promote the asymmetric [4+2] exo-cycloaddition reaction between 1-phenyl-3,4-dimethylphosphole and vinyldiphenylphosphine oxide. The resulting P-chiral phosphanorbornene was obtained as a P–O bidenate chelate on the palladium template. The phosphanorbornene (−)-(L) could be liberated from the palladium template as a highly air-sensitive oil by the treatment of the template complex with aqueous potassium cyanide. Upon recoordination to the Au(I) ion, the diphosphine monoxide coordinated to Au(I) as a monodentate ligand via its tertiary phosphorus donor atom to form the linear complex (+)-[(L–P)AuCl]. The chloro ligand and the pendant PO group in the gold complex showed significant hydrophilicity as they both formed hydrogen bondings to a water molecule. However, the neutral gold complex is not soluble in water.

Asymmetric synthesis of a rigid diphosphine ligand containing two phosphorus and four carbon stereogenic centres by means of a chiral palladium complex promoted Diels–Alder reaction

An optically pure diphosphine ligand containing two phosphorus and four carbon stereogenic centres is prepared efficiently by a chiral organopalladium complex promoted asymmetric Diels–Alder reaction between phenyldi[(Z)-prop-1-enyl]phosphine and 1-phenyl-3,4-dimethylphosphole.