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The diphosphine ligand 1,2-bis(diphenylphosphino)benzene (dppbz) reacts with the activated cluster 1,2-Os 3 (CO) 10 (MeCN) 2 (1) at room temperature to furnish a mixture of the triosmium clusters 1,2-Os 3 (CO) 10 (dppbz) (2) and 1,1-Os 3 (CO) 10 (dppbz) (3), along with a trace amount of the hydride cluster HOs 3 (CO) 9 [μ-1,2-PhP(C 6 H 4-η 1)C 6 H 4 PPh 2 ] (4). The dppbz-bridged cluster 2 forms as the kinetically controlled product and irreversibly transforms to the corresponding chelated isomer 3 at ambient temperature. The disposition of the dppbz ligand in 2 and 3 has been established by X-ray crystallography and 31 P NMR spectroscopy, and the kinetics for the conversion 2 f 3 have been followed by UV-vis spectroscopy in toluene over the temperature range 318-343 K. The calculated activation parameters (ΔH q = 21.6(3) kcal/mol; ΔS q =-11(1) eu) and lack of CO inhibition support an intramolecular isomerization mechanism that involves the simultaneous migration of phosphine and CO groups about the cluster polyhedron. The reaction between 1 and the fluorinated diphosphine ligand 1,2-bis(diphenylphosphino)tetrafluorobenzene (dppbzF 4) was examined under similar reaction conditions and was found to afford the chelated cluster 1,1-Os 3 (CO) 10 (dppbzF 4) (6) as the sole observable product. The absence of the expected bridged isomer 1,2-Os 3 (CO) 10 (dppbzF 4) (5) suggests that the dppbzF 4 ligand destabilizes 5, thus accounting for the rapid isomerization of 5 to 6. Near-UV irradiation of clusters 3 and 6 leads to CO loss and ortho metalation of an ancillary aryl group. The resulting hydride clusters 4 and HOs 3 (CO) 9 [μ-1,2-PhP(C 6 H 4-η 1)C 6 F 4 PPh 2 ] (7) have been isolated and fully characterized by spectroscopic and X-ray diffraction analyses. Both 4 and 7 react with added CO under mild conditions to regenerate 3 and 6, respectively, in quantitative yield. The rearrangements of bridged to chelated diphosphine complexes in this genre of decacarbonyl clusters have been investigated by DFT calculations. The computational results support a concerted process, involving the scrambling of equatorial CO and phosphine groups via a classical merry-go-round exchange scheme. The barriers computed for this mechanism agree well with those that have been measured, and steric compression within the bridged diphosphine groups of the reactants has been calculated to reduce the barrier heights for the rearrangement.

The present study compares the mechanical properties and electrochemical behaviour of austenitic (AISI 316 L) stainless steel compacted at different pressures (200, 400 and 600 MPa), which are conventionally sintered at supersolidus temperature of 1,400°C. As expected, increase in compaction pressure (from 200 MPa) to 600 MPa has shown decreased shrinkage (from 7.3% to 4.2% radial and 5.5% to 3.4% axial, respectively) and increased densification (up to ~92%). Their electrochemical behaviour was investigated in 0.1 N H2SO4 solution by potentiodynamic polarization and electrochemical impedance spectroscopy. The mechanical properties (such as yield-, tensile- and transverse rupture strength) and electrochemical behaviour with pressure have been correlated with densification response and microstructure (pore type, volume and morphology). Highest densification (~92% theoretical) achieved at 600 MPa (compaction pressure) and 1,400°C (sintering temperature) resulted in excellent combination of tensile strength and ductility (456 ± 40 MPa and 25 ± 1.1% respectively), while showing lowest corrosion rate (0.1 mmpy or 4.7 mpy) due to the presence of isolated porosity in the sintered samples.

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