Synthesis, Redox Chemistry, and Electronic Structures of bis-di(silylamido)silane f- element Complexes

We report the synthesis and characterization of pseudo-tetrahedral f-element complexes bearing the sterically demanding bidentate di(silylamido)silane ligand, {Me2Si(NSiiPr3)2}2– (Me2SiN†N†). Reaction of two equivalents of its dipotassium salt, [Me2SiN†N†K2] (1), with either MIIII3(THF)n (M = Ce, Pr, n = 4; M = Tb, n = 3.5) or [UIV(BH4)4]n to afford trivalent polymeric [MIII(Me2SiN†N†)2{K(η6 -toluene)2}]n (2M; M = Ce, Pr, Tb) and tetravalent molecular [UIV(Me2SiN†N†)2] (3U) respectively. We found that complex 2Ce could be readily oxidized to the tetravalent [CeIV(Me2SiN†N†)2] (3Ce), but 2Pr and 2Tb were unyielding towards oxidation under the same conditions. We investigated the electrochemical accessibility of the M(IV/III) redox couples in 2M (M = Ce, Pr, Tb), and 3M (M = Ce, U). For 2Ce and 3Ce we found near-equivalent quasi-reversible processes of the Ce(IV/III) redox couple, with Epc = –1.19 V vs [Fc]+/0. Complexes 2Pr and 2Tb showed oxidation events likely attributable to ligand oxidation only. For complex 3U we were able to electrochemically access the U(IV/III), U(V/IV), and U(VI/V) redox couples with E1/2 of –2.38, –0.89, and –0.11 V vs [Fc]+/0 respectively. All complexes have been characterized variously by single-crystal X-ray diffraction, multinuclear NMR, UV-Vis-NIR, and IR spectroscopies, SQUID magnetometry, and elemental analyses as appropriate. Electronic structure calculations have been employed to validate experimentally observed redox potentials for 3Ce. In the case of synthetically inaccessible 3Pr and 3Tb, we find evidence of ligand oxidation.