SYNTHESIS AND CHARACTERIZATION OF CYCLOPENTADIENYL AND PENTAMETHYLCYCLOPENTADIENYL RUTHENIUM COMPLEXES OF OLIGOTHIOPHENES

We report the synthesis and characterization of 14 complexes of the ge neral form [CpRu(oligothiophene)]PF6 and [CpRu(oligothiophene)]PF6 (C p = eta(5)-cyclopentadienyl; Cp = eta(5)-pentamethylcyclopentadienyl) . The complexes were synthesized from [CpRu(CH3CN)(3)]PF6 or [CpRu(CH 3CN)(3)]PF6 and the appropriate oligothiophene via procedures previous ly reported for other [Cp/CpRu(eta(6)-arene)]PF6 sandwich complexes. For the oligothiophenes 2,2'-bithiophene (Bth), 2,2':5',2 ''-terthioph ene (Tth), 2,2':5',2 '':5 '',2'''-quaterthiophene (Qth), and 5,5 ''-di methyl-2,2':5',2 ''-terthiophene (Me(2)Tth), the Ru is bound eta(5) to the outermost thiophene ring while the complexes of the oligothiophen e 5,5 ''-diphenyl-2,2':5',2 ''-terthiophene (Ph(2)Tth) have Ru bound e ta(6) to a pendant phenyl group. The complexes with ruthenium bound to an arene are very stable with respect to decomplexation; complexes wi th ruthenium bound to a thiophene ring art stable in the solid state a nd in dichloromethane solutions; in acetone, rearrangement reactions o ccur to produce equilibrium mixtures of free oligothiophene and mono- and diruthenated species. Detailed analysis of H-1 and C-13 NMR spectr a, H-1-H-1 decoupling experiments. heteronuclear multiple-bond correla tion (HMBC), and heteronuclear multiple-quantum coherence (HMQC) exper iments enabled the assignment of all H-1 and C-13 resonances. These as signments show that binding ruthenium to a thiophene ring of an oligot hiophene shifts the bound ring resonances upfield and the unbound thio phene rings downfield. The coordination of ruthenium exerts a larger e lectronic effect in oligothiophene complexes than in polyaromatic comp lexes (quaterphenyl). Complexation of a thiophene ring by ruthenium wi ll affect the electronic structure of up to five thiophene rings: the bound ring and the next two unbound thiophene rings on either side.