Mixed-valent interactions in rigid dinuclear systems: electrochemical and spectroscopic studies of CrICr0 ions with controlled torsion of the biphenyl bridge

TLDR: In this paper, three dinuclear complexes were prepared in which Cr(CO) 2 (PPh 3 ) moieties are connected through biphenyl linkages, and each monocation was shown by IR spectroscopy to be trapped-valent.

Abstract: Three dinuclear complexes were prepared in which Cr(CO) 2 (PPh 3 ) moieties are connected through biphenyl linkages. The dihedral (twist) angle of the two arenes in the biphenyl decreases from 100 to 17 to 0 o as the bridging ligand is changed from biphenyl-2,2'-dicarboxylic acid dimethyl ester to dihydrophenanthrene to fluorene. All three compounds are oxidized in two reversible one-electron steps with a voltage separation of ca. 260 mV. Each monocation is shown by IR spectroscopy to be trapped-valent. ESR spectroscopy in frozen glasses gives the same result. IR sampling of the dications is achieved by low-temperature flow electrochemical experiments