Selective reactions of functionalized ruthenium(II) σ-alkynyl complexes with dicobalt octacarbonyl and tetracobalt dodecacarbonyl:: Synthesis of cyclopentenone derivatives via intermolecular Pauson-Khand reactions

Treatment of [Ru{C=CCPh2(C=CH)}(eta(5)-C9H7)(PPh3)(2)] (1) With [Co-2(CO)(8)] leads to the formation of the adduct [Ru{C=CCPh2(mu(2)-eta(2)-C=CH)Co-2(CO)(6)}(eta(5)-C9H7)(PPh3)(2)] (3) through the selective coordination of the Co-2(CO)(6) fragment at the terminal alkyne group on 1. Similarly, the enynyl complex [Ru{C=CCH=CH(C=CPh)}(eta(5)-C9H7)(PPh3)(2)] ((E,Z)-2), prepared via a Wittig reaction from [Ru{C=CCH2(PPh3)}(eta(5)-C9H7)(PPh3)(2)][PF6] (5) and phenylpropargyl aldehyde, also reacts with [Co-2(CO)(8)] to yield selectively the adduct [Ru-{C=CCH=CH(mu(2)-eta(2)-C=CPh)Co-2(CO)(6)}(eta(5)-C9H7(PPh3)(2)] ((E,Z)-6). Protonation of complexes 3 and (E,Z)-6 with HBF4 . Et2O affords the cationic vinylidene derivatives [Ru{=C=C(H)-CPh2(mu(2)-eta(2)-C=CH)Co-2(CO)(6)}(eta(5)-C9H7)(PP3)(2)][BF4] (4) and [Ru{=C=C(H)CH=CH(mu(2)-eta(2)-C=CPh)Co-2(CO)(6)}(eta(5)-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 [Co-4(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.