Preparation of Multinuclear Ruthenium Vinylideneomplexes and The Diels-Alder Reaction of Rutheniuminylidene Complexes

Treatment of [Ru]-Cl ([Ru] = Cp(PEt3)2Ru) with propyne in the presence of KPF6 in methanol affords {[Ru]=C=C(H)Me}[PF6] (2). Deprotonation of 2 with NaOMe yields complex [Ru]-C≡C-Me (3) isolated as yellow solid in high yield. Alkylation of 3 with HC≡CCH2Br in the presence of KPF6 yields the air-stable cationic vinylidene complex {[Ru]=C=C(Me)CH2C≡CH}[PF6] (4a) in high yield. Complexes {[Ru]=C=C(Me)CH2R}[PF6] (4b, R = CH=CH2; 4c, R = CO2Et) are similarly prepared from the corresponding halides in high yield. Reaction of the terminal alkynyl group of 4a with [Ru]-Cl affords the bisvinylidene complex {[Ru]=C=C(Me)CH2C(H)=C=[Ru]}[2PF6] (5) which deprotonates to give the ruthenium vinylidene acetylide complex {[Ru]=C=C(Me)CH2C≡C-[Ru]}[PF6] (6) in the presence of base. Alkylations of complex 6 with various primary alkyl halides RCH2X afford the corresponding cationic ruthenium bis-vinylidene complexes {[Ru]=C=C(Me)CH2C(CH2R)=C=[Ru]}[2PF6], (7a, R = C≡CH; 7b, R = CH=CH2, 7c, R = CO2Et, 7d, R = CO2Me). The trinuclear tris-vinylidene complex {[Ru]=C=C(Me)CH2C(CH2CH=C=[Ru])=C=[Ru]}[3PF6] (8) was prepared by treatment of a methanol solution of 7a with [Ru]-Cl containing KPF6. number of 1,5-enynes have been synthesized. The reaction of [Ru]-Cl with these enynes generates the corresponding vinylidene complexes {[Ru]=C=CHCH(R)CH2CH=CH2}[PF6] (9a, R = 9-chloro-10-anthracenyl; 9b, R = p-C6H4F; 9c, R = p-C6H4OMe). Treatment of complexes 9a-9c with NaOMe in MeOH causes the formation of ruthenium acetylide complexes [Ru]-C≡CCH(R)CH2CH=CH2 (10a, R = 9-chloro-10-anthracenyl; 10b, R = p-C6H4F; 10c, R = p-C6H4OMe). Alkylation of 10c with propargyl bromide affords the cationic ruthenium vinylidene complex {[Ru]=C=C(CH2C≡CH)CH(p-C6H4OMe)CH2CH=CH2}[PF6] (11c). Conversion to the alkylation products {[Ru]=C=C(CH2R)CH(C14H8Cl)CH2CH=CH2}[PF6] (11aa, R = CH=CH2; 11ab, R = CO2Et; 11ac, R = C(CH3)=CH2) were also achieved by the reaction of 10a with the corresponding primary halides. Surprisingly complex 11aa containing two allylic groups undergoes the Diels-Alder reaction between the anthracene and the terminal vinyl group of the allylic at Cβ. In dichloromethane, the cationic complex 11aa completely transforms into complex 12aa at 40°C for three days. Complex 11ac, dissolved in CH2Cl2 at 40 oC under nitrogen for one day, was not converted to the Diels-Alder reaction product 12ac yet. Only under more forcing condition, e.g. at 60 oC for 2 days, complex 11ac will transform to complex 12ac completely. The methyl group of dienophile encumbers the approach to the diene, so it must raise the temperature for the Diels-Alder reaction.he light yellow acetylide complex [Ru]-C≡CC(p-C6H5OMe)2CH2C≡CH (14a) was obtained from the reaction of ruthenium allenylidene complex {[Ru]=C=C=C(p-C6H5OMe)2}[PF6] (13a) with Grignard reagent HC≡CCH2MgBr in THF. Under similar reaction conditions, vinylidene complexes {[Ru]=C=CHC(C4H3O)2CH2R’}[PF6] (15be, R = C≡CH; 15bf, R = CH=CH2) were also obtained by reaction of {[Ru]=C=C=C(C4H3O)2}[PF6] (13b) with the corresponding Grignard reagents. Protonation of 14a gave the vinylidene complex [Ru]=C=C(H)CH(p-C6H5OMe)2CH2C≡CH}[PF6] (15ab) and methylation of 14a with methyliodide afforded the vinylidene complex {[Ru]=C=C(Me)CH(p-C6H5OMe)2CH2C≡CH}[PF6] (15a) in essentially quantitative yield. Another type of bis-vinylidene complex {[Ru]=C=C(Me)C(p-C6H5OMe)2CH2CH=C=[Ru]}[2PF6] (16a) has been synthesized from complex 15a, [Ru]-Cl and KPF6 in MeOH. Deprotonation of 16a with NaOMe afforded only decomposition to unidentified complexes.reatment of [Ru]-Cl with 1-(1-allylcyclohexyl)prop-2-yn-1-ol (17) in the presence of AgPF6 in CH2Cl2 leads to the cationic ruthenium allenylidene complex {[Ru]=C=C=CHC(C5H10)CH2CH=CH2}[PF6] (18a). Reaction of complex [Os]-Br ([Os] = Cp(PPh3)2Os) with 17 in the presence of KPF6 in methanol generates the vinylidene complex {[Os]=C=CHCH(OMe)C(C5H10)CH2CH=CH2}[PF6] (19b) possibly via the formation of allenylidene intermediate followed by methoxy group addition at Cγ. Deprotonation of the complex 19b in the presence of NaOMe leads to the acetylide complex 20b, [Os]-C≡CCH(p-PhOMe)CH2CH=CH2, isolated as yellow solid in high yield.