Cationic Diiron and Dirutheniumμ-Allenyl Complexes: Synthesis, X-Ray Structures and Cyclization Reactions with Ethyldiazoacetate/Amine Affording Unprecedented Butenolide- and Furaniminium-Substituted Bridging Carbene Ligands

Abstract

The novel cationic diiron μ-allenyl complexes [Fe₂Cp₂(CO)₂(μ-CO){μ-η¹:η²_α,β-C_α(H)C_βC_γ(R)₂}]⁺ (R = Me, 4a; R = Ph, 4b) have been obtained in good yields by a two-step reaction starting from [Fe₂Cp₂(CO)₄]. The solid state structures of [4a][CF₃SO₃] and of the diruthenium analogues [Ru₂Cp₂(CO)₂(μ-CO){μ-η¹:η²_α,β-C_α(H)C_βC_γ(R)₂}][BPh₄] (R = Me, [2a][BPh₄]; R = Ph, [2c][BPh₄]) have been ascertained by X-ray diffraction studies. The reactions of 2c and 4a with Brønsted bases result in formation of the μ-allenylidene compound [Ru₂Cp₂(CO)₂(μ-CO){μ-η¹:η¹-C_αC_βC_γ(Ph)₂}] (5) and of the dimetallacyclopentenone [Fe₂Cp₂(CO)(μ-CO){μ-η¹:η³-C_α(H)C_β(C_γ(Me)CH₂)C(O)}] (6), respectively. The nitrile adducts [Ru₂Cp₂(CO)(NCMe)(μ-CO){μ-η¹:η²-C_α(H)C_βC_γ(R)₂}]⁺ (R = Me, 7a; R = Ph, 7b), prepared by treatment of 2a,c with MeCN/Me₃NO, react with N₂CHCO₂Et/NEt₃ at room temperature, affording the butenolide-substituted carbene complexes [Ru₂Cp₂(CO)(μ-CO){μ-η¹:η³-C_α(H)C_βC_γ(R)₂OC(O)C(H)] (R = Me, 10a; R = Ph, 10b). The intermediate cationic compound [Ru₂Cp₂(CO)(μ-CO){μ-η¹:η³-C_α(H)C_βC_γ(Me)₂OC(OEt)C(H)]⁺ (9) has been detected in the course of the reaction leading to 10a. The addition of N₂CHCO₂Et/NHEt₂ to 7a gives the 2-furaniminium-carbene [Ru₂Cp₂(CO)(μ-CO){μ-η¹:η³-C_α(H)C_βC_γ(Me)₂OC(OEt)C(H)]⁺ (11). The X-ray structures of 10a, 10b and [11][BF₄] have been determined. The reactions of 4a,b with MeCN/Me₃NO result in prevalent decomposition to mononuclear iron species.