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Reactions of Diazo Compounds at μ-Vinyliminium Ligands:  Synthesis of Novel Dinuclear Azine−Bis(alkylidene) Complexes

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posted on 03.04.2020, 15:30 by Luigi Busetto, Fabio Marchetti, Stefano Zacchini, Valerio Zanotti
The vinyliminium complexes [M2{μ-η13-Cγ(R‘)CβHCαN(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (1af) react with ethyl diazoacetate in the presence of NaH, affording the azine−bis(alkylidene) [M2{μ-η12-Cγ(R‘)Cβ{NNCδ(COOMe)H}CαN(Me)(R)}(μ-CO)(CO)(Cp)2] (M = Fe, R = 2,6-Me2C6H3 (Xyl), R‘ = Me (2a), p-C6H4Me (Tol) (2b), CO2Me (2c), Bun (2d); M = Fe, R = R‘ = Me (2e); M = Ru, R = Xyl, R‘ = Me (2f)) in 70÷77% yields. Analogous reactions with N2CPh2 lead to the formation of [Fe2{μ-η12-Cγ(R‘)Cβ(NNCδPh2)CαN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (R‘ = Me (3a), COOMe (3b)). The azine−bis(alkylidene) ligand easily undergoes electrophilic addition, affording the cationic hydrazone−vinyliminium complexes [Fe2{μ-η13-Cγ(R‘)Cβ{N(E)NCδ(R‘ ‘)(R‘ ‘‘)}CαN(Me)(Xyl)}(μ-CO)(CO)(Cp)2]+ (R‘ = Me, R‘ ‘ = CO2Et, R‘ ‘‘ = E = H, 4a; R‘ = Me, R‘ ‘ = COOEt, R‘ ‘‘ = H, E = Me, 4b; R‘ = Bun, R‘ ‘ = COOEt, R‘ ‘‘ = H, E = Me, 4c; R‘ = Me, R‘ ‘ = R‘ ‘‘ = Ph, E = Me, 4d). Reactions of 4b,d with NaBH4 result in the addition of hydride at the Cα of the vinyliminium moiety, generating the bridging allylidene complexes [Fe2{μ-η13-Cγ(Me)Cβ{N(Me)NCδ(R‘ ‘)(R‘ ‘‘)}Cα(H)N(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (R‘ ‘ = CO2Et, R‘ ‘‘ = H, 5a; R‘ ‘ = R‘ ‘‘ = Ph, 5b), respectively. The X-ray molecular structures of 2a and 4c[CF3SO3]·CH2Cl2 have been determined.