Nucleophilic additions of anionic Group 6 carbene complexes on cationic indenyl–ruthenium(II) allenylidene derivatives: an easy entry to bimetallic complexes containing σ-alkynyl–carbene and vinylidene–carbene bridges

Abstract

The novel indenyl–ruthenium(II) allenylidene complexes [Ru{CCC(R)Ph}(η⁵-C₉H₇)(PPh₃)L][PF₆] (L = PMePh₂, R = Ph 4a, H 4b; L = PMe₂Ph, R = Ph 5) have been prepared by reaction of [RuCl(η⁵-C₉H₇)(PPh₃)L] (L = PMePh₂2, PMe₂Ph 3) with HCCC(OH)(R)Ph and NaPF₆ in methanol. These allenylidene derivatives as well as [Ru{CCC(R)Ph}(η⁵-C₉H₇)(PPh₃)₂][PF₆] (R = Ph 1a, H 1b) undergo regioselective nucleophilic additions of anionic Fischer type carbene complexes [Li][(CO)₅M{C(OMe)CH₂}] (M = Cr, W, Mo) at the C_γ atom of the unsaturated chain to afford the neutral bimetallic σ-alkynyl derivatives [Ru(CCC(R)Ph{CH₂C(OMe)M(CO)₅})(η⁵-C₉H₇)(PPh₃)L] (L = PPh₃, R = Ph, M = Cr 6a, W 6b, Mo 6c; L = PPh₃, R = H, M = Cr 7a, W 7b; L = PMePh₂, R = Ph, M = Cr 8a, W 8b; L = PMePh₂, R = H, M = Cr 9a, W 9b; L = PMe₂Ph, R = Ph, M = Cr 10a, W 10b). Protonation of these derivatives with HBF₄·Et₂O yields cationic vinylidene complexes [Ru(CC(H)C(R)Ph{CH₂C(OMe)M(CO)₅})(η⁵-C₉H₇)(PPh₃)L][BF₄] 11a–c, 12–15a,b which represent the first examples of bimetallic species containing a vinylidene–carbene bridge. Heating under reflux solutions of vinylidene complexes 11b and 12b in acetonitrile affords the carbene derivatives [(CO)₅W{C(OMe)CH₂C(R)Ph(CCH)}] (R = Ph 16a, H 16b) and the nitrile complex [Ru(NCMe)(η⁵-C₉H₇)(PPh₃)₂][BF₄] 17. The diphenylallenylidene complex 1a regioselectively reacts with NaCN to yield the σ-alkynyl derivative [Ru{CCCPh₂(CN)}(η⁵-C₉H₇)(PPh₃)₂] 18. Treatment of 18 with one equivalent of [M(CO)₅(THF)] leads to the formation of the bimetallic σ-alkynyl complexes [Ru(CCCPh₂{CN–M(CO)₅})(η⁵-C₉H₇)(PPh₃)₂] (M = Cr 20a, W 20b, Mo 20c).