Palladacyclo-promoted asymmetric hydrophosphination reaction between diphenylphosphine and 2-ethynylpyridine

• Asymmetric hydrophosphination reaction of 2-ethynylpyridine was reported.
• A new chiral diphosphine ligand was synthesized.
• The organopalladium complex has been successfully used as the chiral template.

The organopalladium complex containing ortho-metalated (R)-[1-(dimethylamino) ethyl]naphthalene as the chiral auxiliary has been used as the chiral template to promote the asymmetric hydrophosphination reaction between diphenylphosphine and 2-ethynylpyridine in high selectivity under mild conditions. The double hydrophosphination reaction produces four stereoisomeric products in the ratio of 1:19.4:2.4:1.3. The naphthylamine auxiliary could be removed chemoselectively from the template products by treatment with concentrated hydrochloric acid to form the corresponding chiral dichloro complexes [(P–P)PdCl2]. The molecular structure and absolute configuration of the dichloro complex have been resolved by single-crystal X-ray crystallography. It confirms that the asymmetric diphosphines as P–P bidentate chelate on the chiral naphthylamine palladium templates. Finally, the enantiomerically pure diphosphine ligand with chirality on the carbon backbone can be readily liberated from the dichloro palladium complex as an air-sensitive solid by treatment of the complex with aqueous potassium cyanide in high yield.

Asymmetric hydrophosphination reaction between diphenylphosphine and 2-ethynylpyridine was promoted by the palladium complex containing ortho-metalated (R)-[1-(dimethylamino)ethyl]naphthalene as the chiral auxiliary.Figure optionsDownload as PowerPoint slide