James V. McArdle

Carbene precursors and metal complexes : The synthesis and structure of dichloro(difluoromehtyl)- carbonylbis(triphenylphosphine)iridium(III), IrCl2(CHF2)(CO)- (PPh3)2

The complex IrCl 2 (CHF 2 )(CO)(PPh 3 ) 2 is synthesized by the thermal decomposition of IrCl(CHF 2 )(OCOCF 2 Cl)(CO)(PPh 3 ) 2 or by the extended reaction of Vaskas complex, IrCl(CO)(PPh 3 ) 2 , with the carbene precursor CF 2 ClCOONa. The crystal and molecular structure of IrCl 2 (CHF 2 )(CO)(PPh 3 ) 2 has been determined from three dimensional X-ray data by standard heavy atom methods. The complex crystallizes in space group P 2 2 / c of the monoclinic system in a cell of dimensions a 10.47(1), b 14.45(2), c 24.58(2) A, β 97.68(5) o and V 3865 A 3 . The molecular structure of the complex consists of a slightly distorted octahedron with trans phosphine ligands. The difluoromethyl group is trans to a chlorine atom with an IrC(1) distance of 2.19(3) A. the existence of the proton of the difluoromethyl group is suggested by the bond angles about C(1), and is confirmed by a deuterium labelling experiment. The thermal composition of IrCl(CHF 2 )(OCOCF 2 Cl)(CO)(PPh 3 ) 2 to give IrCl 2 (CHF 2 )(CO)(PPh 3 ) 2 in quantitative yield is discussed as a means of generating CF 2 . Extension to other O - coordinated α-halocarboxylates is proposed.

Structure and Electron Transfer Reactions of Blue Copper Proteins

Complete assignments of the electronic spectra of stellacyanin, plastocyanin, and azurin have been made. Bands attributable to d-d transitions have been located in the near-infrared region for the first time, and their positions are consistent with a distorted tetrahedral geometry for the blue copper center. The kinetics of the electron transfer reactions of stellacyanin, azurin, and plastocyanin with Fe(EDTA)^(2-) and Co(phen)_3^(3+) have been studied. Kinetic parameters indicate that reduction of azurin and plastocyanin by Fe(EDTA)^(2-) occurs by long distance transfer to a buried blue copper center. However, the pathway for oxidation involves substantial protein rearrangement, thereby allowing contact of Co(phen)_3^(3+) with the copper ligands. In contrast, the blue copper center of stellacyanin is equally accessible in solution to redox agents.

Studies on the redox characteristics of ferrioxamine E.

Thermodynamic parameters for the reduction of ferrioxamine E as calculated from redox potentials determined at four different temperatures were found to be ΔH≠=7.1±3.4 kJ mol−1 and ΔS≠=−146 J mol−1 K−1. The negative entropy value is large, because the decrease in the charge at the metal center and an increase in its ionic radius force the structure of the complex to become less rigid and resemble the desferrisiderophore. The hydrophilic groups of the system are now (relatively more) available for solvent interaction. Thus, a large negative entropy change accompanies the reduction of the complex. Kinetics of reduction of ferrioxamine by VII, CrII, EuII, and dithionite were measured at different temperatures and by dithionite at different pH values. The CrII and EuII reactions proceed by an inner‐sphere mechanism and have second‐order rate constants at 25° of 1.37×104 and 1.23×105 M−1 s−1, respectively. For the VII reduction, the corresponding rate constant was 1.89×103 M−1 s−1. The activation parameters for the VII reduction were ΔH≠ = 8.3 kJ mol−1; ΔS≠ =−154 J mol−1 K−1. These values are indicative of an outer‐sphere mechanism for VII reduction. The reduction by dithionite is half order in dithionite concentration indicating that SO

Coordination chemistry of microbial iron transport compounds. 19. Stability constants and electrochemical behavior of ferric enterobactin and model complexes

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Siderophore electrochemistry: relation to intracellular iron release mechanism

. is the sole reducing species. log of reduction rate constants of different trihydroxamates by this reductant were correlated with their respective redox potentials, and the variation was found to be in approximate correspondence with the expectations of Marcus relationship.