Synthesis, Spectroscopy and Spectroelectrochemistry of Chlorocarbonyl {1,2-Bis[(2,6-diisopropylphenyl)imino]acenaphthene-κ2-N,N'}rhodium(I)

Reaction of the dinuclear complex [{Rh(CO)₂}₂(μ-Cl)₂] with an α-diimine ligand, 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (iPr₂Ph-bian), produces square-planar [RhCl(CO)(iPr₂Ph-bian)]. For the first time, 2:1 and 1:1 α-diimine/dimer reactions yielded the same product. The rigidity of iPr₂Ph-bian together with its flexible electronic properties and steric requirements of the 2,6-diisopropyl substituents on the benzene rings allow rapid closure of a chelate bond and replacement of a CO ligand instead of chloride. A resonance Raman study of [RhCl(CO)(iPr₂Ph-bian)] has revealed a predominant Rh-to-bian charge transfer (MLCT) character of electronic transitions in the visible spectral region. The stabilisation of [RhCl(CO)(iPr₂Ph-bian)] in lower oxidation states by the π-acceptor iPr₂Ph-bian ligand was investigated in situ by UV-VIS, IR and EPR spectroelectrochemistry at variable temperatures. The construction of the novel UV-VIS-NIR-IR low-temperature OTTLE cell used in these studies is described in the last part of the paper.