Selective Reactions of Functionalized Ruthenium(II) σ-Alkynyl Complexes with Dicobalt Octacarbonyl and Tetracobalt Dodecacarbonyl: Synthesis of Cyclopentenone Derivatives via Intermolecular Pauson−Khand Reactions

Abstract

Treatment of [Ru{C⋮CCPh2(C⋮CH)}(η5-C9H7)(PPh3)2] (1) with [Co2(CO)8] leads to the formation of the adduct [Ru{C⋮CCPh2(μ2-η2-C⋮CH)Co2(CO)6}(η5-C9H7)(PPh3)2] (3) through the selective coordination of the Co2(CO)6 fragment at the terminal alkyne group on 1. Similarly, the enynyl complex [Ru{C⋮CCHCH(C⋮CPh)}(η5-C9H7)(PPh3)2] ((E,Z)-2), prepared via a Wittig reaction from [Ru{C⋮CCH2(PPh3)}(η5-C9H7)(PPh3)2][PF6] (5) and phenylpropargyl aldehyde, also reacts with [Co2(CO)8] to yield selectively the adduct [Ru{C⋮CCHCH(μ2-η2-C⋮CPh)Co2(CO)6}(η5-C9H7)(PPh3)2] ((E,Z)-6). Protonation of complexes 3 and (E,Z)-6 with HBF4·Et2O affords the cationic vinylidene derivatives [Ru{CC(H)CPh2(μ2-η2-C⋮CH)Co2(CO)6}(η5-C9H7)(PPh3)2][BF4] (4) and [Ru{CC(H)CHCH(μ2-η2-C⋮CPh)Co2(CO)6}(η5-C9H7)(PPh3)2][BF4] ((E,Z)-7), respectively. Dicobalt adduct complexes 3 and (E,Z)-6 undergo Pauson−Khand cyclization processes with strained cyclic alkenes (norbornadiene and norbornene) to afford regioselectively the tricyclic cyclopentenone derivatives 8a,b, 9a,b, (E,Z)-10, and 11. (E,Z)-6 reacts with [Co4(CO)12] to give an unprecedented ruthenium(II) vinylidene complex containing a tetranuclear “butterfly” type cobalt cluster (12), which has been characterized by X-ray diffraction.