Synthesis and Structural Studies of Rhenium(V) Complexes Stabilized by a Monoanionic Cyclen Ligand

Abstract

(2), respectively. The X-ray structural analyses of 3a and 4, as well as 1 H NMR spectroscopy, showed that the macrocyclic ligand is coordinated in the unprecedented monoanionic form.1 H and 13 C NMR spectroscopy also demonstrated that 3a,b and 4 exist in solution as single isomers. To the best of our knowledge, 3a and 4 are the first examples of structurally characterized oxo complexes of d transition elements with cyclen bound to the metal atom through one amido and three amine

cis-Dioxorhenium(V/VI) Complexes Supported by Neutral Tetradentate N4 Ligands. Synthesis, Characterization, and Spectroscopy

“…There is one report on a cis -dioxorhenium­(V) complex containing a tetradentate ligand. Reaction of cis -[Re V (O) 2 I­(PPh 3 ) 2 ] with an achiral neutral tetradentate ligand, 1,4,7,10-tetrazacyclododecane (cyclen), was reported to give octahedral cis -[Re V (O) 2 (cyclen)] + on the basis of 1 H NMR analysis; however, this complex has not been characterized by X-ray crystal analysis and could not be isolated in pure form . In contrast to the structures of cis -dioxorhenium­(V) complexes, their spectroscopy has been much less studied.…”

Rhenium(v) oxocomplexes with novel pyrazolyl-based N4- and N3S-donor chelators

“…By contrast, the loosely bound water ligand in molecule B of 13 (Re(2)-O(5), 2.306(3) A ˚)25 is not expected to compete in an extensive way with the oxo-ligand.Concerning the coordination of the tetradentate ancillary ligands the Re-N pz , Re-N amine , Re-N amide and Re-S bond distances can be considered normal, taking into account the values reported for the same bond distances in other Re(V) complexes with pyrazolyl containing ligands, 26,27 polyamines 28,29 and MAG3 (mercaptoacetyltriglycine) chelators. 12,21,30,31 In particular, the short Re-N(3) bond distance of 1.913(8) A ˚in compound 11 is consistent with a certain double character for the coordination of the deprotonated and almost planar sp 2 -hybridized nitrogen atom 28. This bond distance is considerably shorter than the Re-N amine bond distances in 11 (2.090(8)-2.299(8) A ˚), being more comparable to the Re-N amido bond distances in 13 (1.981(4)-2.040 A ˚).Labelling studies: syntheses and in vitro evaluation of [ 99m TcO{pz(CH 2 ) 2 -NH-Gly-CH 2 S}] (12a) The stability of the complexes [ReO{pz*(CH 2 ) 2 -NH-Gly-CH 2 S}] (pz* = pz (12), 3,5-Me 2 pz (13), 4-(EtOOCCH 2 )-3,5-Me 2 pz (14)),…”

Proton-assisted Two-electron Transfer in Natural Variants of Tetraheme Cytochromes from Desulfomicrobium Sp.

“…Mechanistic Interpretation of the Functional Thermodynamic Properties-The hypothesis is that the physiological function of type I cytochrome c 3 is to accept electrons and protons from the periplasmic hydrogenase and deliver them to membrane-linked proteins, including the type II cytochrome c 3 , with a net energy transfer from the redox to the protonic centers (5,7,17). There are several requirements for a soluble protein to act as an efficient electron-proton energy transducer, not all of which can be established by studying the protein in isolation (61,62).…”

“…Furthermore, their reduction potentials are very negative and pH-dependent in the physiological range (redox-Bohr effect) (3,4). Together, these properties allow cytochromes c 3 to couple the transfer of electrons and protons (5), which for type I cytochrome c 3 (2) is fundamental for its physiological function as partner of the periplasmic hydrogenase (6,7). The Desulfomicrobium norvegicum (Dsmn) cytochrome c 3 has been proposed to be involved in electron transfer between the [NiFeSe] hydrogenase and the octaheme cytochrome c 3 (8) in a similar way as that for type I and type II cytochromes c 3 from Desulfovibrio africanus (2).…”