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

The novel cationic diiron m-allenyl complexes [Fe(2)Cp(2)(CO)(2)(mu-CO){mu-eta(1):eta(2)(alpha,beta)-C(alpha)(H)=C(bet a)=C(gamma)(R)(2)}](+) (R = Me, 4a; R = Ph, 4b) have been obtained in good yields by a two-step reaction starting from [Fe(2)Cp(2)(CO)(4)]. The solid state structures of [4a][CF(3)SO(3)] and of the diruthenium analogues [Ru(2)Cp(2)(CO)(2)(mu-CO){mu-eta(1):eta(2)(alpha,beta)-C(alpha)(H)=C(bet a)=C(gamma)(R)(2)}][BPh(4)] (R= Me, [2a][BPh(4)]; R = Ph, [2c][BPh(4)]) have been ascertained by X-ray diffraction studies. The reactions of 2c and 4a with Bronsted bases result in formation of the mu-allenylidene compound [Ru(2)Cp(2)(CO)(2)(mu-CO){mu-eta(1):eta(1)-C(alpha)=C(beta)=C(gamma)(Ph) (2)}] (5) and of the dimetallacyclopentenone [Fe(2)Cp(2)(CO)(mu-CO){mu-eta(1):eta(3)-C(alpha)(H)=C(beta)(C(gamma)(Me) CH(2))C(=O)}] (6), respectively. The nitrile adducts [Ru(2)Cp(2)(CO)(NCMe)(mu-CO){mu-eta(1):eta(2)-C(alpha)(H)=C(beta)=C(gamm a)(R)(2)}](+) (R = Me, 7a; R = Ph, 7b), prepared by treatment of 2a, c with MeCN/Me(3)NO, react with N(2)CHCO(2)Et/ NEt(3) at room temperature, affording the butenolide-substituted carbene complexes [Ru(2)Cp(2)(CO)(mu-CO){mu-eta(1):eta(3)-C(alpha)(H)C(beta)C(gamma)(R)(2) OC(=O)C(H)] (R = Me, 10a; R = Ph, 10b). The intermediate cationic compound [Ru(2)Cp(2)(CO)(mu-CO){mu-eta(1):eta(3)-C(alpha)(H)C(beta)C(gamma)(Me)(2 )OC(OEt)C(H)](+) (9) has been detected in the course of the reaction leading to 10a. The addition of N(2)CHCO(2)Et/NHEt(2) to 7a gives the 2-furaniminium-carbene [Ru(2)Cp(2)(CO)(mu-CO){mu-eta(1):eta(3)-C(alpha)(H)C(beta)C(gamma)(Me)(2 )OC(OEt)C(H)](+) (11). The X-ray structures of 10a, 10b and [11][BF(4)] have been determined. The reactions of 4a, b with MeCN/Me(3)NO result in prevalent decomposition to mononuclear iron species.