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Coordination Chemistry of Disilylated Germylenes with Group 4 Metallocenes.

ABSTRACT: Reaction of the PEt₃ adduct of a disilylated five-membered cyclic germylene with group 4 metallocene dichlorides in the presence of magnesium led to the formation of the respective germylene metallocene phosphine complexes of titanium, zirconium, and hafnium. Attempts to react the related NHC adduct of a disilylated four-membered cyclic germylene under the same conditions with Cp₂TiCl₂ did not give the expected germylene NHC titanocene complex. This complex was, however, obtained in the reaction of Cp₂Ti(btmsa) with the NHC germylene adduct. A computational analysis of the structure of the group 4 metallocene germylene complexes revealed the multiple-bond character of the M-Ge(II) linkage, which can be rationalized with the classical ?-donor/?-acceptor interaction. The strength of the M-Ge(II) bond increases descending group 4.

SUBMITTER: Hlina J

PROVIDER: S-EPMC3714165 | biostudies-literature | 2013 Jun

REPOSITORIES: biostudies-literature

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Coordination Chemistry of Disilylated Germylenes with Group 4 Metallocenes.

Hlina Johann J Baumgartner Judith J Marschner Christoph C Zark Patrick P Müller Thomas T

Organometallics 20130517 11

Reaction of the PEt3 adduct of a disilylated five-membered cyclic germylene with group 4 metallocene dichlorides in the presence of magnesium led to the formation of the respective germylene metallocene phosphine complexes of titanium, zirconium, and hafnium. Attempts to react the related NHC adduct of a disilylated four-membered cyclic germylene under the same conditions with Cp2TiCl2 did not give the expected germylene NHC titanocene complex. This complex was, ...[more]

PMID: 23874053

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Project description:This Account focuses on the coordination chemistry of the microbial iron chelators called siderophores. The initial research (early 1970s) focused on simple analogs of siderophores, which included hydroxamate, catecholate, or hydroxycarboxylate ligands. The subsequent work increasingly focused on the transport of siderophores and their microbial iron transport. Since these are pseudo-octahedral complexes often composed of bidentate ligands, there is chirality at the metal center that in principle is independent of the ligand chirality. It has been shown in many cases that chiral recognition of the complex occurs. Many techniques have been used to elucidate the iron uptake processes in both Gram-positive (single membrane) and Gram-negative (double membrane) bacteria. These have included the use of radioactive labels (of ligand, metal, or both), kinetically inert metal complexes, and Mössbauer spectroscopy. In general, siderophore recognition and transport involves receptors that recognize the metal chelate portion of the iron-siderophore complex. A second, to date less commonly found, mechanism called the siderophore shuttle involves the receptor binding an apo-siderophore. Since one of the primary ways that microbes compete with each other for iron stores is the strength of their competing siderophore complexes, it became important early on to characterize the solution thermodynamics of these species. Since the acidity of siderophores varies significantly, just the stability constant does not give a direct measure of the relative competitive strength of binding. For this reason, the pM value is compared. The pM, like pH, is a measure of the negative log of the free metal ion concentration, typically calculated at pH 7.4, and standard total concentrations of metal and ligand. The characterization of the electronic structure of ferric siderophores has done much to help explain the high stability of these complexes. A new chapter in siderophore science has emerged with the characterization of what are now called siderocalins. Initially found as a protein of the human innate immune system, these proteins bind both ferric and apo-siderophores to inactivate the siderophore transport system and hence deny iron to an invading pathogenic microbe. Siderocalins also can play a role in iron transport of the host, particularly in the early stages of fetal development. Finally, it is speculated that the molecular targets of siderocalins in different species differ based on the siderophore structures of the most important bacterial pathogens of those species.

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Coordination Chemistry of Disilylated Germylenes with Group 4 Metallocenes.

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Coordination Chemistry of Disilylated Germylenes with Group 4 Metallocenes.

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