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

Abstract

The optically active allenylidene complex [Ru{CCC(C₉H₁₆)}(η⁵-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 σ-alkynyl derivatives [Ru{CCC(C₉H₁₆)R}(η⁵-C₉H₇)(PPh₃)₂] (R = H 2a, CN 2b, Me 2c, CCPh 2d). Protonation of 2a–d with HBF₄·Et₂O affords the cationic vinylidene complexes [Ru{CC(H)C(C₉H₁₆)R}(η⁵-C₉H₇)(PPh₃)₂][BF₄] 3a–d, which can be easily demetalated, by treatment with acetonitrile, yielding the corresponding chiral acetylenic compounds HCC(C₉H₁₆)R 4a–d. The novel optically active indenyl–ruthenium(II) allenylidene complexes [Ru{CCC(C₉H₁₆)}(η⁵-C₉H₇)(PPh₃)₂][PF₆] (C(C₉H₁₆) = (1R,4R)-1,7,7-trimethyl-bicyclo[2.2.1]hept-2-ylidene) 9 and [Ru{CCC(C₉H₁₄)}(η⁵-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(η⁵-C₉H₇)(PPh₃)₂] 6. Treatment of 9 with anionic nucleophiles generates the neutral σ-enynyl complex [Ru{CCC(C₉H₁₅)}(η⁵-C₉H₇)(PPh₃)₂] 11 (C(C₉H₁₅) = (1R,4R)-1,7,7-trimethyl-bicyclo[2.2.1]hept-2-en-2-yl).