Pyridyl- and pyrimidyl-phosphine-substituted [FeFe]-hydrogenase mimics: Synthesis, charaterization and properties

Two tetranuclear iron–sulphur complexes {[(μ-pdt)Fe2(CO)5]2(PNP) (2) and [(μ-pdt)Fe2(CO)5]2(PNNP) (3)} and three dinuclear ones {[(μ-pdt)Fe2(CO)5](PNP) (4), [(μ-pdt)Fe2(CO)5](PNNP) (5) and [(μ-pdt)Fe2(CO)5](PNN) (6)} were synthesized, using two new pyrimidyl-phosphine ligands PNNP [4,6-bis(diphenylphosphino) pyrimidine] and PNN (4-tertiary butyl-6-diphenylphosphino pyrimidine) together with the reported pyridyl-phosphine PNP [bis(diphenylphosphino)pyridine] as substituents to react with Fe2(μ-pdt)(CO)6. The molecular structures of 2, 3 and 6 were confirmed by single-crystal X-ray analyses, which show that all phosphine ligands occupy the apical positions, while the space group of 3 (P21/n) is different from that of 2 (P-1). Cyclic voltammograms reveal that pyrimidyl-phosphine substituted complexes 3, 5 and 6 present two reduction waves in CH2Cl2 solutions, while pyridyl-phosphine substituted 2 and 4 show only one. The DFT computational studies demonstrate that the contributions to the LUMO of 3 are comparable from the two Fe2S2 centres and ligated PNNP ligand, which is different from those of other [Fe2S2] mimics in this work.