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⋮CCPh 2 (C⋮CH)}(η 5 -C 9 H 7 )(PPh 3 ) 2 ] ( 1 ) with [Co 2 (CO) 8 ] leads to the formation of the adduct [Ru{C⋮CCPh 2 (μ 2 -η 2 -C⋮CH)Co 2 (CO) 6 }(η 5 -C 9 H 7 )(PPh 3 ) 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)}(η 5 -C 9 H 7 )(PPh 3 ) 2 ] (( E,Z )- 2 ), prepared via a Wittig reaction from [Ru{C⋮CCH 2 (PPh 3 )}(η 5 -C 9 H 7 )(PPh 3 ) 2 ][PF 6 ] ( 5 ) and phenylpropargyl aldehyde, also reacts with [Co 2 (CO) 8 ] to yield selectively the adduct [Ru{C⋮CCH CH(μ 2 -η 2 -C⋮CPh)Co 2 (CO) 6 }(η 5 -C 9 H 7 )(PPh 3 ) 2 ] (( E,Z )- 6 ). Protonation of complexes 3 and ( E,Z )- 6 with HBF 4 ·Et 2 O affords the cationic vinylidene derivatives [Ru{ C C(H)CPh 2 (μ 2 -η 2 -C⋮CH)Co 2 (CO) 6 }(η 5 -C 9 H 7 )(PPh 3 ) 2 ][BF 4 ] ( 4 ) and [Ru{ C C(H)CH CH(μ 2 -η 2 -C⋮CPh)Co 2 (CO) 6 }(η 5 -C 9 H 7 )(PPh 3 ) 2 ][BF 4 ] (( 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.