Reactions of Ru(Ctriple barCPh)(PPh(3))(2)Cp* with tetracyanoethene: cycloaddition, formation of unusual n(2)-CNR complexes and oligomerisation via bridging cyanocarbon ligands

Thermolysis of Ru{η³-C(CN)₂CPhC=C(CN)₂}(PPh₃)Cp* (2), obtained from Ru(C≡CPh)(PPh₃)₂Cp* and tetracyanoethene, has given the three complexes Ru{η¹,η²(C,N)-C(CN)=C(CN)CPh=C(CN)(C=N)}(PPh₃)Cp* (3), {Ru(PPh₃)Cp*}{μ-N:η³-NCC(CN)=CPhC=C(CN)₂}{μ-η¹:N-C(CN)=C(CN)CPh=C(CN)₂}{RuCp*} (4) and {Ru[η³-C(CN)₂=CPhC=C(CN)₂]Cp*}₃ (5). All four complexes have been characterised by single-crystal X-ray structure determinations and contain isomeric forms of the C₄(CN)₄Ph ligand. Unusual features of the molecular structures are (i) the presence of a side-on (η²) CN group in 3; (ii) formation of a second isomer of the polycyanocarbon ligand by CN migration to an adjacent carbon, in 3 and 4; (iii) the use of one or more CN groups to bridge ruthenium centres in 4 and 5; and (iv) the complete loss of PPh₃ ligands during the formation of the trimer 5. Although there are three crystallographically distinct RuCp* groups in 5, only one Cp* resonance is found in solution NMR spectra, suggesting that oligomer formation by facile CN–Ru bond breaking and making is occurring.Michael I. Bruce, Brian W. Skelton, Allan H. White and Natasha N. Zaitsev