Reduction-oxidation properties of organo-transition metal complexes XXXIV. Superoxide and semi-quinone derivatives of the triazenido-bridged 4+ unit

Article abstract of DOI:10.1016/0022-328X(91)86029-P

The ³⁺-containing complex ⁺ (1; R = p-tolyl) undergoes carbonyl substitution with molecular oxygen to give ⁺ (4), the ESR spectrum of which shows a superoxide ligand bound to an ⁴⁺ core.By contrast, the complex ⁺ (2) binds O2, again as a superoxide ligand, in the adduct ⁺ (3).In a similar reaction involving co-ordination of a redox-active ligand and intramolecular metal-ligand electron-transfer, 1 and the o-quinone o-O2C6Cl4 (o-chloranil, tetrachloro-1,2-benzoquinone) give ⁺ (5) in which the O,O-chelate, in the o-benzosemiquinone form, is bonded to an ⁴⁺ centre.The cyclic voltammogram of 5 shows two oxidation and two reduction waves at a platinum electrode in CH2Cl2, and electrochemical or chemical (with ferrocene) reduction yields the diamagnetic catecholate-⁴⁺ complex 6.