Reactions of Ru(C≡CPh)(PPh₃)₂Cp* with tetracyanoethene: cycloaddition, formation of unusual ŋ²-CNR complexes and oligomerisation via bridging cyanocarbon ligands

Abstract

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.