A "conjugal" consanguineous family of butadiynediyl-derived complexes: Synthesis and electronic ground states of neutral, radical cationic, and dicationic iron/rhenium C-4 species

The reaction of (eta(5)-C5MeS)Re(NO)(PPh3)(C=CC=CSiMe3) and (eta(5)-C5Me5)F e(eta(2)-dppe)(Cl) with KF, KPF6, and 18-crown-6 in MeOH/THF gives the hete robimetallic butadiynediyl complex (eta(5)-C5Me5)Re-(NO)(PPh3)(C=CC=C)(eta( 2)-dppe)Fe(eta(5)-C5Me5) (9, 65%). This can be oxidized with [(eta(5)-(C5H5 )(2)Fe)](+) PF6- to the isolable radical cation 9(+) PF6- and dication 9(2) 2PF(6)(-), which constitute the first conjugal consanguineous family of C -x complexes. The crystal structure of 9 is determined, and 9(n+) nPF(6)(-) are characterized in detail by cyclic voltammetry (CV) and IR, NMR, near-I R, ESR, and Fe-57 Mossbauer spectroscopies. The bond lengths/angles suggest some bridge polarization in 9, and CV data show that the iron and rhenium endgroups communicate strongly. The odd electron in 9(+) PF6- is delocalize d between the endgroups. In 9(2+) 2PF(6)(-), both electronic and magnetic i nteractions are found between remote unpaired spins on the rhenium and iron endgroups. This antiferromagnetic coupling stabilizes the singlet cumuleni c over the tripler butadiynediyl state. At room temperature, however, both isomers of 9(2+) 2PF(6)(-) are simultaneously present. Data are carefully c ompared to those of the analogous consanguineous diiron and dirhenium compl exes.