Indenyl-ruthenium(II) allenylidene complexes containing terpenic substituents as precursors of optically active terminal alkynes: scope and limitations

The optically active allenylidene complex [Ru{C=C=C(C9H16)}((eta)5-C9H7)(PPh3)2][PF6](C(C9H16)=(1R,4S)-1,3,3-trimethyl-bicyclo [2.2.1]hept-2-ylidene)1 regio- and stereoselectively reacts with unhindered anionic nucleophiles to yield the neutral (sigma) -alkynyl derivatives [Ru{C(identical)CC(C9H16)R} ((eta)5-C9H7)(PPh3)2](R = H 2a, C(identical)N 2b, Me 2c, C(identical)CPh 2d). Protonation of 2a-d with HBF4·Et2O affords the cationic vinylidene complexes [Ru{=C=C(H)C(C9H16)R}((eta)^5-C9H7)(PPh3)2][BF4]3a-d, which can be easily demetalated, by treatment with acetonitrile, yielding the corresponding chiral acetylenic compounds HC(identical)C(C9H16)R 4a-d. The novel optically active indenyl-ruthenium(II) allenylidene complexes [Ru{C=C=C(C9H16)}((eta)^5-C9H7)(PPh3)2][PF6](C (C9H16)=(1R,4R)-1,7,7-trimethyl-bicyclo[2.2.1]hept-2-ylidene)9 and [Ru{C=C=C(C9H14)}((eta)^5-C9H7)(PPh3)2][PF6](C(C9H14)= (1S,5S)-4,6,6-trimethyl-bicyclo[3.1.1]hept-3-en-2-ylidene)10 have been prepared by activation of propargylic alcohols derived from the natural ketones (+)-camphor and (-)-verbenone, respectively, with [RuCl((eta)^5-C9H7)(PPh3)2]6. Treatment of 9 with anionic nucleophiles generates the neutral (sigma)-enynyl complex [Ru{C(identical)CC(C9H15)}((eta)^-C9H7)(PPh3)2]11(C(C9H15)=(1R,4R)1,7,7-trimethyl-bicyclo[2.2.1]hept-2-en-2-yl).