Synthesis and Characterization of a Series of Structurally and Electronically Diverse Fe(II) Complexes Featuring a Family of Triphenylamido-Amine Ligands

A family of triphenylamido-amine ligands of the general stoichiometry LxH3 = [R−NH−(2-C6H4)]3N (R = 4-t-BuPh (L1H3), 3,5-t-Bu2Ph (L2H3), 3,5-(CF3)2Ph (L3H3), CO-t-Bu (L4H3), 3,5-Cl2Ph (L5H3), COPh (L6H3), CO-i-Pr (L7H3), COCF3 (L8H3), and i-Pr (L9H3)) has been synthesized and characterized, featuring a rigid triphenylamido-amine scaffold and an array of stereoelectronically diverse aryl, acyl, and alkyl substituents (R). These ligands are deprotonated by potassium hydride in THF or DMA and reacted with anhydrous FeCl2 to afford a series of ferrous complexes, exhibiting stoichiometric variation and structural complexity. The prevalent [(Lx)Fe(II)−solv]− structures (Lx = L1, L2, L3, L5, solv = THF; Lx = L8, solv = DMA; Lx = L6, L8, solv = MeCN) reveal a distorted trigonal bipyramidal geometry, featuring ligand-derived [N3,amidoNamine] coordination and solvent attachment trans to the Namine atom. Specifically for [(L8)Fe(II)−DMA]−, a Namido residue is coordinated as the corresponding Nimino moiety (Fe−N(Ar)C(CF3)−O−). In contrast, compounds [(L4)Fe(II)]−, [(L6)2Fe(II)2]2−, [K(L7)2Fe(II)2]22−, and [K(L9)Fe]2 are all solvent-free in their coordination sphere and exhibit four-coordinate geometries of significant diversity. In particular, [(L4)Fe(II)]− demonstrates coordination of one amidato residue via the O-atom end (Fe−O−C(t-Bu)N(Ar)). Furthermore, [(L6)2Fe(II)2]2− and [K(L7)2Fe(II)2]22− are similar structures exhibiting bridging amidato residues (Fe−N(Ar)−C(R)O−Fe) in dimeric structural units. Finally, the structure of [K(L9)Fe]2 is the only example featuring a minimal [N3,amidoNamine] coordination sphere around each Fe(II) site. All compounds have been characterized by a variety of physicochemical techniques, including Mössbauer spectroscopy and electrochemistry, to reveal electronic attributes that are responsible for a range of Fe(II)/Fe(III) redox potentials exceeding 1.0 V.