Selective and efficient cycloisomerization of alkynols catalyzed by a new ruthenium complex with a tetradentate nitrogen-phosphorus mixed ligand.

The new ruthenium complex [Ru(N(3)P)(OAc)][BPh(4)] (4), in which N(3)P is the N,P mixed tetradentate ligand N,N-bis[(pyridin-2-yl)methyl]-[2-(diphenylphosphino)phenyl]methanamine was synthesized. The complex was found to be catalytically active for the endo cycloisomerization of alkynols. The catalytic reactions can be used to synthesize five-, six-, and seven-membered endo-cyclic enol ethers in good to excellent yields. A catalytic cycle involving a vinylidene intermediate was proposed for the catalytic reactions. Treatment of complex 4 with PhC[triple bond]CH and H(2)O gave the alkyl complex [Ru(CH(2)Ph)(CO)(N(3)P)][BPh(4)] (30), which supports the assumption that the catalytic reactions involve addition of a hydroxyl group to the C=C bond of vinylidene ligands.