Synthesis and Chemical Redox Studies of Half-Sandwich Chromium Carbonyl Azobenzenes

Chemical oxidation of piano-stool complexes Cr(CO)3(TripNNTrip) (1) and Cr(CO)3(TripNNTrip)Cr(CO)3 (2) was investigated, which led to a CAArN cation (cyc-1+) and a 17-electron chromic radical cation (2•+) upon one-electron oxidation reactions, respectively. The reactivity of cation cyc-1+ was extensively investigated. The electrophilicity enables cyc-1+ to form Lewis adducts with Me3P. Cyc-1+ can be reduced by metal K to form neutral monoradical cyc-1• and react with p-benzoquinone to produce a diradical dication salt (X). The electronic properties of 2•+ were investigated by single-crystal X-ray diffraction and EPR spectroscopy, in conjunction with DFT calculations.