Rama Acharyya

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 L(x)H(3) = [R-NH-(2-C(6)H(4))](3)N (R = 4-t-BuPh (L(1)H(3)), 3,5-t-Bu(2)Ph (L(2)H(3)), 3,5-(CF(3))(2)Ph (L(3)H(3)), CO-t-Bu (L(4)H(3)), 3,5-Cl(2)Ph (L(5)H(3)), COPh (L(6)H(3)), CO-i-Pr (L(7)H(3)), COCF(3) (L(8)H(3)), and i-Pr (L(9)H(3))) 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 FeCl(2) to afford a series of ferrous complexes, exhibiting stoichiometric variation and structural complexity. The prevalent [(L(x))Fe(II)-solv](-) structures (L(x) = L(1), L(2), L(3), L(5), solv = THF; L(x) = L(8), solv = DMA; L(x) = L(6), L(8), solv = MeCN) reveal a distorted trigonal bipyramidal geometry, featuring ligand-derived [N(3,amido)N(amine)] coordination and solvent attachment trans to the N(amine) atom. Specifically for [(L(8))Fe(II)-DMA](-), a N(amido) residue is coordinated as the corresponding N(imino) moiety (Fe-N(Ar) horizontal lineC(CF(3))-O(-)). In contrast, compounds [(L(4))Fe(II)](-), [(L(6))(2)Fe(II)(2)](2-), [K(L(7))(2)Fe(II)(2)](2)(2-), and [K(L(9))Fe](2) are all solvent-free in their coordination sphere and exhibit four-coordinate geometries of significant diversity. In particular, [(L(4))Fe(II)](-) demonstrates coordination of one amidato residue via the O-atom end (Fe-O-C(t-Bu) horizontal lineN(Ar)). Furthermore, [(L(6))(2)Fe(II)(2)](2-) and [K(L(7))(2)Fe(II)(2)](2)(2-) are similar structures exhibiting bridging amidato residues (Fe-N(Ar)-C(R) horizontal lineO-Fe) in dimeric structural units. Finally, the structure of [K(L(9))Fe](2) is the only example featuring a minimal [N(3,amido)N(amine)] coordination sphere around each Fe(II) site. All compounds have been characterized by a variety of physicochemical techniques, including Mossbauer spectroscopy and electrochemistry, to reveal electronic attributes that are responsible for a range of Fe(II)/Fe(III) redox potentials exceeding 1.0 V.

Synthesis, structure and electrochemical properties of some oxime complexes of rhodium

Reaction of the oximes of salicyladehyde (H2L1), 2-hydroxyacetophenone (H2L2) and 2-hydroxynaphthaldehyde (H2L3; general abbreviation H2L, where H2 stands for the two dissociable protons, one phenolic proton and one oxime proton) with [Rh(PPh3)3Cl] afforded a family of rhodium(III) complexes of the type [Rh(PPh3)2(HL)(L)]. The crystal structure of [Rh(PPh3)2(HL2)(L2)] has been determined by X-ray diffraction. One oxime ligand is coordinated via dissociation of only the phenolic proton, while the other oxime ligand is coordinated via dissociation of both the phenolic and oxime protons. Both the oxime ligands are coordinated as bidentate N,O-donors, forming six-membered chelate rings. The complexes are diamagnetic (low-spin d6, S = 0) and their 1H NMR spectra are in excellent agreement with their compositions. All three [Rh(PPh3)2(HL)(L)] complexes display intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry on all the complexes shows two oxidations; the first one is observed within the range 0.61 to 0.76 V vs. SCE and the second one within 1.20 to 1.32 V vs. SCE. There is also one irreversible reduction between −1.05 and −1.30 V vs. SCE.