Convincing evidence for the presence of a nitrogen atom in the dithiolate bridge of the active site of native [FeFe] hydrogenases (B) is provided by a spectroscopic, electrochemical, and theoretical study of a well‐characterized structural mimic of the [FeFe] hydrogenase subcluster (picture: 14N matched‐HYSCORE spectrum of the model compound A). This result should help to understand the mechanism of dihydrogen conversion and production.

A series of [FeFe]-hydrogenase active site analogues, with the general formula [Fe(2)(dt)(CO)(4)(BC)] 1-3 (dt = dithiolate, pdt = propyl-1,3-dt (1), bdt = benzene-1,2-dt (2), edt = ethyl-1,2-dt (3); BC = 1,2-bisdiphenylphosphine-1,2-o-carborane), has been prepared and structurally characterized. While the electrochemical reductions of 1-3 are largely invariant to the different nature of their dt bridges, the oxidations differ by more than 120 mV in between the series. Remarkably, all three compounds are reversibly oxidized, with complex 1 that contains the most electron-donating pdt ligand at the mildest potential of -0.09 V vs. Fc/Fc(+). The one-electron oxidized state 1(ox) is stable for several minutes and was spectroscopically characterized by FTIR and EPR. EPR spectroscopy provided evidence that in the mixed-valence [Fe(I)Fe(II)] state most of the spin density is located on the iron with the BC-ligand. This is monitored through the strong (31)P hyperfine coupling of the phenyl groups of the BC ligand, while further delocalization into the o-carborane unit is negligible.

Überzeugende Beweise für das Vorhandensein eines Stickstoffatoms in der Dithiolatbrücke des aktiven Zentrums von natürlichen [FeFe]‐Hydrogenasen B liefert die spektroskopische, elektrochemische und theoretische Untersuchung eines gut charakterisierten Strukturmodells der [FeFe]‐Hydrogenasen (siehe 14N‐Matched‐HYSCORE‐Spektrum der Modellverbindung A). Dies ist von großer Bedeutung für das Verständnis des Mechanismus der Wasserstoffkonversion und ‐produktion in diesem hochaktiven Enzym.

Single oxides of Ti and Zr incorporated SBA-15 were prepared and characterized by N 2 adsorption, NMR, and XPS techniques. 29 Si MAS NMR results suggest the formation of Si-O-X linkages (X: Ti or Zr) by an increase in the ratio of Q 3 /Q 4 in the presence of Ti or Zr. XPS analysis of Ti-SBA-15 catalysts indicate the presence of Ti-O-Si bonds in addition to Ti-O-Ti and Si-O-Si bonds, supporting the NMR evidence.