Thomas N. Sorrell

Observation of 17O effects on MoV EPR spectra in sulfite oxidase; xanthine dehydrogenase, and MoO(SC6H5)4−

Abstract 17 O effects have been observed on the Mo V EPR signals from sulfite oxidase, xanthine dehydrogenase, and MoO(SC 6 H 5 ) 4 − . The results point to the presence of a rapidly exchangeable oxygen ligand in the molybdenum coordination sphere of the enzymes. Average splittings were on the order of 10 gauss for the enzymes, but only about 2 gauss for MoO(SC 6 H 5 ) 4 − .

An Improved Synthesis of 2,2′-Dimercaptobiphenyl

Abstract The preparation of transition-metal thiolato complexes as synthetic biomimics1 has led to a resurgent interest in the synthesis of organic thiols and their derivatives. The compound 2,2′-dimercaptobiphenyl, 1, offers interesting possibilities as a ligand, and it has been used recently to displace iron-sulfur clusters from low molecular-weight Fe-S proteins.2 The two previous preparations for 1 require a coupling reaction of diazonium salts.3,4 Overall yields of 10%3 and 30%4 are made even less attractive by the need to precipitate copper by-products with H2S after the coupling step.

Modeling the active site in hemocyanin: synthesis and reactivity of binuclear copper complexes

Abstract Binucleating ligands that provide three nitrogen donors, and in some cases a phenolate group, to each copper ion have been synthesized. Introduction of substituents to provide steric shielding of the presumed dioxygen-binding site in a previously-described complex prevents reaction of these new species with dioxygen. That these changes are not a direct consequence of steric effects is demonstrated by the synthesis of a Cu(II) derivative having a bridging acetate group. Thus, seemingly simple structural modifications of model systems for the hemocyanin active site may cause substantial changes in reactivity.

Synthesis and structural characterization of a Cu(I) dimer of a tris(oxazoline) ligand

Abstract The synthesis of a new tripodal tris(oxazoline) ligand, tris[4,4-dimethyl-2-(4,5-dihydrooxazolyl)]methylamine is described, and details of the X-ray crystal_structure of its Cu(I) complex are presented. The complex crystallizes as a dimer in the triclinic space group P 1 . Each Cu(I) ion is coordinated in a distorted trigonal geometry by two oxazoline groups from one tripod and a third oxazoline from the second ligand. The Cu(I)-Cu(I) distance is 5.7 A. The CO adduct of the complex exhibits ν(CO)= 2066 cm −1 .

Development of bio-inspired chelates with hydrogen bond donors: synthesis and structure of monomeric metal acetate complexes with intramolecular hydrogen bonds

The synthesis of the new multidentate tripodal compounds bis[(N′-tert-butylureido)-N-ethyl]-2-pyridylmethylamine (H41) and bis[(N′-tert-butylureido)-N-ethyl]-N-methylamine (H42) is described. These ligands contain two urea-ethylene arms that when deprotonated and bound to a metal ion, position two hydrogen bond donors near the metal center so that formation of intramolecular H-bonds with other coordinated species is possible. The complexes K[MII(H21)(η1-OAc)] and K[MII(H22)(η2-OAc)] (MII = Co and Fe) have been isolated and characterized. The multidentate ligands mediate the mode of acetate coordination: the [MII(H21)(η1-OAc)]− complexes have a monodentate coordination, whereas in [MII(H22)(η2-OAc)]− the acetate binds in a bidentate manner. X-Ray diffraction studies reveal that all complexes have trigonal bipyramidal coordination geometries with one of the acetate oxygen atoms being nearly trans to the amine nitrogen donor. All the complexes have relatively long M–O bond lengths in comparison with other MII–OAc complexes characterized previously. The complexes exhibit intramolecular H-bonds from the urea NH groups to one of the coordinated oxygen atoms of the acetate, causing a lengthening of the MII–OAc bond distances. The NH⋯O bond lengths and vibrational energies in these acetate complexes support weaker H-bonds than the H-bonding interactions in similar ligand complexes with hydroxo ligands.

A bidentate ligand with appended hydrogen bond donors:: synthesis and structure of four-coordinate metal complexes with bis[(tert-butyl)aminocarbonyl]-1,2-diaminoethane

Abstract The secondary coordination sphere in the active sites of metalloproteins is instrumental in controlling function. Non-covalent interactions, such as hydrogen bonds, are often used to create unique microenvironments around the metal ion(s). To duplicate these effects in synthetic complexes, first row transition metal complexes of the ligand bis[(tert-butyl)aminocarbonyl]-1,2-diaminoethane (H41) have been synthesized and structurally characterized. Twofold deprotonation of H41 affords the dianionic, bidentate ligand [H21]2−, which forms the four-coordinate complexes [MII(H21)2]2−. X-ray diffraction studies on [MII(H21)2]2− (M=Fe, Co, Zn) show that these complexes have pseudo-tetrahedral coordination geometry. H-bond donors from [H21]2− surround the metal centers in each complexes, and metrical data suggest that NH⋯M H-bonds are present in these complexes. The square-planar [NiII(H21)]2− has H-bond donors that span both faces of the coordination plane, forming intramolecular H-bonds between the [H21]2− ligands.

Synthesis, structural characterization and dioxygen reactivity of imidazole-ligated Cu(I) complexes

Abstract {Bis[(heterocycle)ethyl]amine}copper(I) complexes with a least one imidazole ligand react with 0.5 equiv. of dioxygen at −78 °C to give purple peroxo species. The dioxygen adduct of { N -2-[(2-pyridyl)ethyl]- N -2-[1-butyl- 2-imidazolyl)ethyl]amine}copper(I) tetrafluoroborate having one imidazole and one pyridine donor has absorption maxima at 332, 435 and 538 nm and is unreactive toward acid and triphenylphosphine at low temperature, characteristics that have been ascribed to μ-η 2 ,η 2 coordination. {Bis[2-(1-methyl-2-imidazolyl)ethyl]amine}copper(I) tetrafluoroborate ( 11 ) has been structurally characterized by X-ray crystallography and has the expected T-shape. Crystal data for 11 : monoclinic, a =9.2181(21), b =11.638(3), c =14.914(4) A; β=92.059(19)°; Z =4; space group= P 2 1 / c ; 1748 independent non-zero ( I >2.5σ( I ) reflections with 2θ between 2 and 50°; R =6.5%; R w =8.5%.

Synthesis of dioxomolybdenum(VI) complexes of heterocyclic-N,O and-N,S ligands

Abstract Benzimidazolylalcohols, benzimidazolylthiols, and pyrazolylphenols react with MoO 2 (acac) 2 to give octahedral MoO 2 L 2 complexes in the case of the N,O ligands but dimeric Mo 2 O 4 L 2 complexes with the N,S ligands. Heterocycles apparently do not provide enough steric bulk to allow generation of skew- trapezoidal complexes.

Imidazole-Ligated Copper Complexes: Synthesis, Structure, and Reactivity

A diverse group of copper-containing proteins carries out the transport and activation of the O2 molecule in biological systems.1–5 Extensive characterization of biomimetic analogs of two of those, namely hemocyanin and tyrosinase, has afforded a better understanding of the inorganic chemistry of peroxocopper complexes at the molecular level.6–12

Magnetic exchange in binuclear copper(II) complexes with dissimilar bridging atoms

Abstract Several copper(II) complexes have been prepared that use binucleating ligands to yield a coordinatively unsaturated product complex. These complexes will accept an exogenous ligand that binds to a bridging position. We have prepared two families of complexes from 5- or 7-coordinate binucleating ligands that exhibit similar magnetic effects as the exogenous bridging ligands are changed. Complexes of the 7-coordinate binucleating ligand are also especially useful as models of the active site of some binuclear copper proteins (e.g. hemocyanin). We report on our results covering a large series of complexes with exogenous bridging ligands B = Cl - , Br - , OH - , CH 3 CO - 2 , 1,1-N - 3 , 1,3-N - 3 , ClO - 4 , etc. The magnetic exchange interaction for these complexes has not yet been observed to be ferromagnetic, but the magnitude of antiferromagnetic interactions range from Curie-Weiss paramagnetism (B = CH 3 COO - ) to diamagnetism (B = 1,3-N - 3 ).