Yin-Qiu Liu

Synthesis and characterisation of three diiron tetracarbonyl complexes related to the diiron centre of [FeFe]-hydrogenase and their protonating, electrochemical investigations

The synthesis, characterisation of three diiron tetracarbonyl complexes, [Fe2(SCH2)2C(Me)(CH2OR)(PNP)(CO)4] (R = H and PNP = L11: 2; R = H and PNP = L22: 3; R = Ts and PNP = L11: 4) as models for the diiron sub-unit of [FeFe]-hydrogenase are described, where OTs, L11 and L22 are toluenesulfonate, (Ph2P)2NCH2(2-C5H4N) and (Ph2P)2NCH2Ph, respectively. These complexes are fully characterised and the structure of complex 4 is crystallographically determined. Protonation of these complexes with HBF4·Et2O is probed by using infrared and NMR spectroscopies which reveals that no hydride can be formed upon addition of the acid. Instead addition of excess of the acid leads to protonating the N atom of the PNP skeleton, which is a weak base due to participating conjugating interactions with the Fe–Fe centre, as revealed by crystallographic analysis. Electrochemistry of these complexes and their electrocatalytic reduction of protons are also investigated. Our results suggest that the existence of the pendant pyridine group can lower the overpotential for proton reduction but does not seem to enhance electrocatalytic efficiency in our case.

Crystal structure of [2-(diphenylphosphino)phenyliminoethyl]- ferrocene, Fe(C5H5)(C25H21NP)

C30H26FeNP, monoclinic, P21/n (no. 14), a = 10.750(2) Å, b = 9.077(2) Å, c = 24.489(5) Å, * = 90.85(3)°, V = 2389.3 Å, Z = 4, Rgt(F) = 0.042, wRref(F) = 0.113, T = 293 K. Source of material The raw material 2-(diphenylphosphino)aniline was prepared by a literature method [1], and acetylferrocene was commercially obtained. Acetylferrocene (1.14 g, 5.0 mmol), 5 Å molecular sieve (2.0 g) and 2-(diphenylphosphino)aniline (1.325 g, 5.0.mmol) were suspended in dried toluene (20 cm). The reaction mixtures were refluxed at stirring for 5 6 day. In order to control the progress of the condensation reaction the infrared spectra of the solutions were recorded. Daily addition of small quantities of the amine (0.2 g, 1 mmol) and molecular sieve (4 Å) was needed to force the displacement of the equilibria. This procedure was repeated for 5 6 day until the infrared spectra of the samples did not exhibit the band due to the asymmetrical stretching of the C=O group of the acetylferrocene [!(C=O) 1662 cm]. Then, the molecular sieves were removed by vacuum filtration and washed with ether until the liquid became colourless. The orange-red solution was concentrated on a rotary evaporator, and the oil formed was treated with methylene dichloride (10 cm). Slow evaporation of the solvent afforded the red crystal of the title compound (1.950 g, yield 81 %). Discussion Ferrocene and its derivatives have attracted much attention for their potential applications as molecular sensors, magnetic and optical materials, and in homogeneous catalysis. Several studies on the Schiff base containing-ferrocene have been reported recently [2-6]. The title molecule is in a trans configuration of the benzene ring and the cyclopentadienyl ring in respect to the N=C11 bond; the dihedral angle between the planes C6-C10 and N/C13-C18 is 45(1)°. In the ferrocen group, the Fe—C bond lengths are within the normal range [7]. The Fe1···Cg1 and Fe1···Cg2 distances are 1.629 Å and 1.634 Å, respectively, and the Cg1···Fe···Cg2 angle is 178.9°, where Cg1 and Cg2 are the centroids of the substituted and unsubstituted Cp rings, respectively. The two Cp rings are almost eclipsed, with a dihedral angle of 1.4° , and the largest torsion angle C2···Cg1···Cg2···C9 is 6.1°. In the triphenylphosphine group, the P atom adopts a slightly distorted pyramidal coordination. Z. Kristallogr. NCS 224 (2009) 649-650 / DOI 10.1524/ncrs.2009.0286 649

(2,2-Bipyridyl N,N′-dioxide-κ2O,O′)trichloridobis(methanol-κO)terbium(III)

In the title complex, [TbCl3(C10H12N2O2)(CH4O)2], each TbIII ion is seven-coordinate in a pentagonal-bipyramidal coordination geometry. A crystallographic twofold rotation axis passes through Tb and one Cl atom.