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†). Two equivalents of the dipotassium salt, [Me2SiN†N†K2] (1), react with either MIIII3(THF)n (M = Ce, Pr, n = 4; M = Tb, n = 3.5) or [UIV(BH4)4]n affording trivalent [MIII(Me2SiN†N†)2{K(η6-toluene)2}]n (2M; M = Ce, Pr, Tb) and tetravalent [UIV(Me2SiN†N†)2] (3U) respectively. Complex 2Ce was oxidized to tetravalent [CeIV(Me2SiN†N†)2] (3Ce) with AgI, but 2Pr and 2Tb were unreactive under these conditions. The electrochemical accessibility of M(IV/III) couples in 2M (M = Ce, Pr, Tb), and 3M (M = Ce, U) were examined by cyclic voltammetry. For 2Ce and 3Ce, a quasi-reversible Ce(IV/III) couple was observed (Epc = –1.19 V vs [Fc]+/0), but complexes 2Pr and 2Tb showed anodic waves attributed to ligand oxidation only – which is supported by computational analyses. For complex 3U, 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 were found. 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 rationalize electrochemical results for 2Pr, 2Tb, and 3Ce.