Copper Hydride Clusters with Cu₉ and Cu₁₃ Frameworks, Showing a Potential for Hydrogen Storage via Fluxional Exchange between Face-Capping and Interstitial Hydrides

Using <i>meso</i>-Ph₂PCH₂P(Ph)(CH₂)₃P(Ph)CH₂PPh₂ (<i>meso</i>-dpmppp), new copper hydride clusters, [Cu₉H₇(<i>meso</i>-dpmppp)₃]X₂ (X = PF₆ (<b>1a</b>), BF₄ (<b>1b</b>), and BPh₄ (<b>1c</b>)), were synthesized and characterized to have a 4,4,4-tricapped trigonal prism (TTP) Cu₉ core. <b>1a,b</b> was converted by treatment with LiBH₄ to [Cu₉H₈(<i>meso</i>-dpmppp)₃]X (X = PF₆ (<b>2a</b>), BF₄ (<b>2b</b>)), which accommodates an additional hydride while retaining the TTP Cu₉ core. In contrast to the static property of the eight face-capping hydrides of <b>2</b>, five of the seven hydrides in <b>1</b> exhibited the fluxional behavior, which could be frozen at -80 °C into four face-capping and one interstitial hydrides. The Cu₉ core of <b>1b</b> could be expanded by treating with Ph₂SiH₂ and [Cu(MeCN)₄]BF₄ to give the centered icosahedral (CIH) Cu₁₃ core of [Cu₁₃H₁₀(<i>meso</i>-dpmppp)₃(MeCN)₃](BF₄)₃ (<b>3</b>). The similar CIH cluster of [Cu₁₃H₁₀(<i>meso</i>-dpmppmNBn)₃(MeCN)₃](BF₄)₃ (<b>4</b>) was also synthesized using <i>meso</i>-Ph₂PCH₂P(Ph)CH₂N(CH₂C₆H₅)CH₂P(Ph)CH₂PPh₂ (<i>meso</i>-dpmppmNBn). Treatment of <b>1a</b> with H₂ (1 atm) in the presence of DBU (1,8-diazabicyclo[5.4.0]-7-undecene) gave <b>2a</b> quantitatively, and <b>2a</b> reacted easily with 1 equiv of TfOH or PhOH to be converted back to <b>1a</b> with concomitant H₂ formation, suggesting a potential for hydrogen storage through the fluxional exchange between face-capping and interstitial hydrides around the TTP scaffold.