Reactions of Ru(CCPh)(L2)Cp* (L2=dppm, dppe) with tetracyanoethene: cycloaddition, formation of monodentate dppm and dppmO complexes and migration of CN to ruthenium

The reaction of C2(CN)4 with Ru(CCPh)(dppm)Cp* in THF has given the anticipated tetracyanobuta-1,3-dien-2-yl complex Ru{C[C(CN)2]CPhC(CN)2}(dppm)Cp* (3). In benzene, η3-cyano-enyl complexes Ru{η3-C[C(CN)2]CPhCC(CN)2}(L)Cp* (L=dppm-P (4) or dppmO (5)) are formed, the latter by adventitious oxidation. On warming, complex 3 rearranges to the cyanoruthenium–ylid complex Ru(CN){C(CN)C[CPhC(CN)2]PPh2CH2PPh2}Cp* (6). A possible reaction sequence, involving a zwitterionic intermediate such as Ru(δ-)(CN){C(CN)C(δ+)CPhC(CN)2}(dppm-P)Cp* D, is discussed. Only the η1-dienyl complex 7 is obtained from Ru(CCPh)(dppe)Cp* and TCNE.