New coupling reactions for the construction of carbon-rich C7 bridged di-ruthenium complexes

This microreview summarizes our work on new reactions to obtain ruthenium(II) binuclear species with seven conjugated carbon atoms between the remote metals in very mild conditions via CC bond formation. (i) The treatment of trans-[Cl(dppe)2RuCCCCSiMe3] with [Fe(C5H5)2]PF6 leads to an unprecedented metal-assisted [2+2] coupling reaction between CγCδ bonds to produce trans-[Cl(dppe)2RuCCH2)CCRu(dppe)2Cl]PF6 including a cyclobutenyl bridge. (ii) Addition of a cationic allenylidene trans-[ClRu(dppe)2(CCC(CH2R1)R2)]BF4 (R1=H, CH3; R2=CH3, Ph) on the CγCδ bond of the diyne trans-[Cl(dppe)2RuCCCCH] leads to ruthenium bimetallic complexes trans-[Cl(dppe)2RuCCC(CH3)C(R1)C(R2)CCRu(dppe)2Cl]BF4 containing a planar delocalized “W”-shaped C7 bridge with tunable pendant groups. These complexes display attractive redox and optical properties with a highly delocalized charge over the conjugated carbon atoms. The crystal structures of trans-[Cl(dppe)2RuCCC(CH3)C(H)C(CH3)CCRu(dppe)2Cl]BF4 and of the annealated complex were solved.