SHORT COMMUNICATION
[9H]+ become clear. The present work points to a trend that to dinuclear species with different modes of substrate bind-
stems, at least in part, from the basicity of zerovalent metal ing though seven-coordinate species, as exemplified in the
centres: protonation of 2e– mixed-valence MIIMЈ0 species formation of a NiW hydrido complex. While [9H]+ has
can afford asymmetrically-bound NiIIHMЈII hydrido com- modest activity for H+ reduction, compounds of the present
plexes, while protonation of metal–metal bonded MIMЈI type have readily tunable redox properties and pKa values,
cores often results in more symmetric, bona fide μ-hydrido and further investigations into such motifs may well be
species.[16]
Hydride [9H]+ exhibits an irreversible reduction at
profitable.
–1.28 V associated with the formation of H2 and 9, the lat-
ter evidenced by the appearance of the 90/+ wave at –0.25 V.
The activity of [9H]+ toward H+ reduction was probed by
Experimental Section
Synthetic procedures for 7–10 and [9H]BF4, structural details, IR,
cyclic voltammetry. Consistent with [9H]+ acting catalyti- NMR and mass spectra, and electrochemical data are available in
the Supporting Information for this paper.
cally, titration with HBF4·OEt2 resulted in an increase in
the reductive current, with an initial linearity indicating a
process second order in [H+] (Figure 5).
CCDC-1409249 (7), CCDC-1409250 (8), CCDC-1409251 (9) and
CCDC-1409252 (10) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
The authors wish to thank Dr. Haijun Yao for assistance with FD
mass spectrometry and Prof. Thomas Rauchfuss for insightful com-
ments. This research was conducted with the U.S. Department of
Energy by its division of Chemical Sciences, Office of Basic Sci-
ences under contract DEFG02-90ER14146.
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4641
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