Synthesis and Reactivity of a Cerium(III) Scorpionate Complex Containing a Redox Non-Innocent 2,2'-Bipyridine Ligand

The Ce(III) hydrotris(3,5-dimethylpyrazolyl) borate complex [Ce(Tp(Me2))(2)(kappa(2)-dmpz)] (1) (Tp(Me2) = {HB(dmpz)(3)}(-); dmpz = 3,5-dimethylpyrazolide) was isolated in fair yield from the reaction of [Ce(I)(3)(THF)(4)] with two equivalents of [K(Tp(Me2))] via the facile decomposition of Tp(Me2). [Ce(Tp(Me2))(2)(bipy)] (2) was synthesized in poor yield by the onepot reaction of [Ce(I)(3)(THF)(4)], bipy (bipy = 2,2'-bipyridine), KC8 and two equivalents of [K(Tp(Me2))] in tetrahydrofuran (THF). The reaction of 2 with N-methylmorpholine-N-oxide produced the known decomposition product [Ce(Tp(Me2))(mu-BOpMe(2))](2) (3) (BOp(Me2) = {HBO(dmpz)(2)}(2-)) in poor yield, presumably by N-O and B-N bond cleavage of a reactive intermediate. The reaction of 2 with trimethylsilylazide gave [Ce(Tp(Me2))(2)(N-3)] (4) in poor yield; the fate of bipy and the trimethylsilyl group is unknown. Complexes 1-4 were characterized by single crystal XRD, NMR and FTIR spectroscopy and elemental analysis. Complex 2 was additionally probed by UV/Vis/NIR and Electron Paramagnetic Resonance (EPR) spectroscopies, Cyclic Voltammetry (CV) and magnetometry, which together indicate a formal 4f(1) Ce(III) center coordinated by a bipy.(-) radical anion in this system.