Substitution of tetracyanoethene by ethynyl-metal complexes gives tricyanovinylethynyl (tricyanobutenynyl) derivatives: syntheses, protonation, and addition of metal-ligand fragments

Abstract

A series of complexes containing the new tricyanovinylethynyl (3,4,4-tricyanobut-3-en-1-ynyl) ligand have been obtained by substitution of a CN group in tetracyanoethene upon reaction with the ethynyl complexes M(C≡CH)(PP)Cp′ (M = Ru, Os, (PP)Cp′ = (PPh 3) 2Cp; M = Ru, PP = dppe, Cp′ = Cp, Cp*). The reactions proceed in higher yield as the metal environment becomes more sterically hindered, the normal [2 + 2]-cycloaddition/ring-opened product M{C[=C(CN) 2]CH=C(CN) 2}(PP)Cp′ also being formed in some cases. The diynyl complex Ru(C≡CC≡CH)(dppe)Cp* reacts with tcne to give only the ring-opened adduct Ru{C≡CC[=C(CN) 2]CH=C(CN) 2}(dppe)Cp*. Protonation (HBF 4 or HPF 6) of Ru{C≡CC(CN)=C(CN) 2}(dppe)Cp* afforded the vinylidene cation [Ru{=C=CHC(CN)=C(CN) 2}(dppe)Cp*] +. A second transition-metal fragment ML n (ML n = Ru(PPh 3) 2Cp, M′(dppe)Cp* (M′ = Ru, Os), RuCl(dppe) 2) can be added to the CN group trans to the metal center; electrochemical, spectroscopic, and computational studies indicate that there is little ground-state delocalization between the metal centers. In the case of the tricyanovinylethynyl derivatives, an intense MLCT (or ML-LCT) transition can be identified in the visible region, which is responsible for the intense blue to purple color of these species; the analogous transition in the vinylidene-based complexes is significantly blue-shifted. The X-ray crystallographically determined structures of several of these complexes are reported. The cations [{Cp*(dppe)Ru}{μ-(C/N)≡CC(CN)=C(CN) (≡C/N)}{M(dppe)Cp*}] + (M = Ru, Os) show some C≡C/C≡N disorder (and associated Ru/Os disorder in the case of the heterometallic example) in the crystals. © 2011 American Chemical Society.