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(mu-Cl) (dbcot)(2) dimers and the bla ligand and were characterized by NMR, X-ray diffraction, and cyclic voltammetry. Both [M-I(dbcot)(bla)(+) complexes are easily oxidized by one electron to form paramagnetic dicationic analogues [M-II(dbcot)(bla)](2+) (M = Rh, Ir). In the solid state, the geometry changes from a distorted trigonal bipyrainid to square pyramidal upon oxidation of the metal from M-I to M-II, 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 [Rh-II(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 [M-II(dbcot)(bla)](2+) plays a minor role (if any at all) in the observed base-mediated reduction processes. Reaction of bla with [Ir(mu-Cl)(coe)](2) (coe = ciscyclooctene) results in oxidative addition of the vinylic C-H bond of coe to the metal center, as evidenced by X-ray diffraction.