Open-Shell Organometallic [MII(dbcot(bislutidylamine)]2+ Complexes (M = Rh, Ir): Unexpected Base-Assisted Reduction of the Metal Instead of Amine Ligand Deprotonation

Cationic rhodium and iridium complexes with dibenzo[a,e]cyclooctatetraene (dbcot) and bislutidylamine (bla) were synthesized from the respective [M(μ-Cl)(dbcot)]2 dimers and the bla ligand and were characterized by NMR, X-ray diffraction, and cyclic voltammetry. Both [MI(dbcot)(bla)]+ complexes are easily oxidized by one electron to form paramagnetic dicationic analogues [MII(dbcot)(bla)]2+ (M = Rh, Ir). In the solid state, the geometry changes from a distorted trigonal bipyramid to square pyramidal upon oxidation of the metal from MI to MII, as evidenced by X-ray diffraction studies of the iridium complexes. The paramagnetic complexes undergo facile one-electron reduction in the presence of base, most likely involving oxidation of the solvent or hydroxide anions. A control experiment using the corresponding [RhII(dbcot)(Bn-bla)]2+ complex, wherein Bn-bla is the N-benzyl-protected bla ligand, gives similar results, which strongly suggests that deprotonation of the N−H moiety of the [MII(dbcot)(bla)]2+ plays a minor role (if any at all) in the observed base-mediated reduction processes. Reaction of bla with [Ir(μ-Cl)(coe)]2 (coe = cis-cyclooctene) results in oxidative addition of the vinylic C−H bond of coe to the metal center, as evidenced by X-ray diffraction.