The P–P bond of the cis-1 ligand in (μ-cis-1)[Fe(CO)4]2 (cis-1 = naphthalene-1,8-diphenyldiphosphine) was cleaved by the two iron centers after CO dissociation from the iron centers, although the P–P bond of cis-1 was stereochemically stabilized with a robust naphthalene group, unlike the usual diphosphines, which lack such support. The resulting (μ-nabip)[Fe(CO)3]2 (3; nabip = naphthalene-1,8-bis(phenylphosphido)) had the diiron core linked by the bisphosphido bridge. Since the trans isomer (μ-trans-1)[Fe(CO)4]2 was stable under ambient conditions, the cis disposition of the two Fe(CO)4 fragments was responsible for the cleavage of the P–P bond. The one or two terminal CO ligands of 3 can be replaced by MeCN and a range of phosphine ligands: i.e., PMe3, PPh3, cis-1, and trans-1. Interestingly, it was found that the diphosphine cis-1 could coordinate the iron center in an unusual κ2 fashion to form a three-membered ring, which was confirmed by NMR spectra as well as X-ray analysis. These diiron complexes can be protonated with the strong acid TfOH in CH2Cl2 to form cationic complexes having a μ-H bridge between the two iron centers. The parent hexacarbonyl complex 3 could act as a proton reduction catalyst at −2.0 V in the presence of TsOH as the proton source in CH2Cl2. When protonated complexes having MeCN or phosphine ligands were used, the proton reduction potentials catalyzed by these complexes were shifted to a more positive range of around −1.77 to −1.37 V, depending on the terminal ligand.

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Mitsubishi Heavy Industries (MHI) has developed SOFC with tubular type cell stack since 1984. In this study, we report the current status toward commercialization of SOFC-GTCC power generation system at MHI. To Redox robustness of a cell stack, the sintering characteristics of interconnect was improved. To improve durability of cell stack, long-term change of the electrochemical characteristics had been measured, and analyzed the interface of cathode and electrolyte by SIMS. For compact module, the packing density of the cell stack was increased from 400 to 700 stack/m2, and confirmed I-V characteristics and the temperature distribution of improved module. The generation performance of improved module is roughly comparable to that of conventional type module, and the temperature distribution is also roughly agreement of simulation result.