Reactions of Ru(CCPh)(PPh3)2Cp* with tetracyanoethene: cycloaddition, formation of unusual η2-CNR complexes and oligomerisation via bridging cyanocarbon ligands

Thermolysis of Ru{η3-C(CN)2CPhCC(CN)2}(PPh3)Cp* (2), obtained from Ru(CCPh)(PPh3)2Cp* and tetracyanoethene, has given the three complexes Ru{η1,η2(C,N)-C(CN)C(CN)CPhC(CN)(CN)}(PPh3)Cp* (3), {Ru(PPh3)Cp*}{μ-N:η3-NCC(CN)CPhCC(CN)2}{μ-η1:N-C(CN)C(CN)CPhC(CN)2}{RuCp*} (4) and {Ru[η3-C(CN)2CPhCC(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.