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Influence of the nacnac Ligand in Iron(I)-Mediated P4 Transformations.

ABSTRACT: A study of P4 transformations at low-valent iron is presented using ?-diketiminato (L) Fe(I) complexes [LFe(tol)] (tol=toluene; L=L(1) (1?a), L(2) (1?b), L(3) (1?c)) with different combinations of aromatic and backbone substituents at the ligand. The products [(LFe)4 (?4 -?(2) :?(2) :?(2) :?(2) -P8 )] (L=L(1) (2?a), L(2) (2?b)) containing a P8 core were obtained by the reaction of 1?a,b with P4 in toluene at room temperature. Using a slightly more sterically encumbered ligand in 1?c results in the formation of [(L(3) Fe)2 (?-?(4) :?(4) -P4 )] (2?c), possessing a cyclo-P4 moiety. Compounds 2?a-c were comprehensively characterized and their electronic structures investigated by SQUID magnetization and (57) Fe Mössbauer spectroscopy as well as by DFT methods.

SUBMITTER: Spitzer F

PROVIDER: S-EPMC4804748 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Influence of the nacnac Ligand in Iron(I)-Mediated P4 Transformations.

Spitzer Fabian F Graßl Christian C Balázs Gábor G Zolnhofer Eva M EM Meyer Karsten K Scheer Manfred M

Angewandte Chemie (International ed. in English) 20160229 13

A study of P4 transformations at low-valent iron is presented using β-diketiminato (L) Fe(I) complexes [LFe(tol)] (tol=toluene; L=L(1) (1 a), L(2) (1 b), L(3) (1 c)) with different combinations of aromatic and backbone substituents at the ligand. The products [(LFe)4 (μ4 -η(2) :η(2) :η(2) :η(2) -P8 )] (L=L(1) (2 a), L(2) (2 b)) containing a P8 core were obtained by the reaction of 1 a,b with P4 in toluene at room temperature. Using a slightly more sterically encumbered ligand in 1 c results in t ...[more]

PMID: 26924606

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Project description:Electrochemical water oxidation is the bottleneck of electrolyzers as even the best catalysts, iridium and ruthenium oxides, have to operate at significant overpotentials. Previously, the position of a hydroxyl on a series of hydroxylpicolinate ligands was found to significantly influence the activity of molecular iridium catalysts in sacrificial oxidant driven water oxidation. In this study, these catalysts were tested under electrochemical conditions and benchmarked to several other known molecular iridium catalysts under the exact same conditions. This allowed us to compare these catalysts directly and observe whether structure-activity relationships would prevail under electrochemical conditions. Using both electrochemical quartz crystal microbalance experiments and X-ray photoelectron spectroscopy, we found that all studied iridium complexes form an iridium deposit on the electrode with binding energies ranging from 62.4 to 62.7 eV for the major Ir 4f7/2 species. These do not match the binding energies found for the parent complexes, which have a broader binding energy range from 61.7 to 62.7 eV and show a clear relationship to the electronegativity induced by the ligands. Moreover, all catalysts performed the electrochemical water oxidation in the same order of magnitude as the maximum currents ranged from 0.2 to 0.6 mA cm-2 once more without clear structure-activity relationships. In addition, by employing 1H NMR spectroscopy we found evidence for Cp* breakdown products such as acetate. Electrodeposited iridium oxide from ligand free [Ir(OH)6]2- or a colloidal iridium oxide nanoparticles solution produces currents almost 2 orders of magnitude higher with a maximum current of 11 mA cm-2. Also, this deposited material contains, apart from an Ir 4f7/2 species at 62.4 eV, an Ir species at 63.6 eV, which is not observed for any deposit formed by the molecular complexes. Thus, the electrodeposited material of the complexes cannot be directly linked to bulk iridium oxide. Small IrOx clusters containing few Ir atoms with partially incorporated ligand residues are the most likely option for the catalytically active electrodeposit. Our results emphasize that structure-activity relationships obtained with sacrificial oxidants do not necessarily translate to electrochemical conditions. Furthermore, other factors, such as electrodeposition and catalyst degradation, play a major role in the electrochemically driven water oxidation and should thus be considered when optimizing molecular catalysts.

Dataset Information

Influence of the nacnac Ligand in Iron(I)-Mediated P4 Transformations.

Publications

Influence of the nacnac Ligand in Iron(I)-Mediated P4 Transformations.

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