Using meso-Ph2PCH2P(Ph)(CH2)3P(Ph)CH2PPh2 (meso-dpmppp), new copper hydride clusters, Cu9H7(meso-dpmppp)3X2 (X = PF6 (1a), BF4 (1b), and BPh4 (1c)), were synthesized and characterized to have a 4,4,4-tricapped trigonal prism (TTP) Cu9 core. 1a,b was converted by treatment with LiBH4 to Cu9H8(meso-dpmppp)3X (X = PF6 (2a), BF4 (2b)), which accommodates an additional hydride while retaining the TTP Cu9 core. In contrast to the static property of the eight face-capping hydrides of 2, five of the seven hydrides in 1 exhibited the fluxional behavior, which could be frozen at −80 °C into four face-capping and one interstitial hydrides. The Cu9 core of 1b could be expanded by treating with Ph2SiH2 and Cu(MeCN)4BF4 to give the centered icosahedral (CIH) Cu13 core of Cu13H10(meso-dpmppp)3(MeCN)3(BF4)3 (3). The similar CIH cluster of Cu13H10(meso-dpmppmNBn)3(MeCN)3(BF4)3 (4) was also synthesized using meso-Ph2PCH2P(Ph)CH2N(CH2C6H5)CH2P(Ph)CH2PPh2 (meso-dpmppmNBn). Treatment of 1a with H2 (1 atm) in the presence of DBU (1,8-diazabicyclo5.4.0-7-undecene) gave 2a quantitatively, and 2a reacted easily with 1 equiv of TfOH or PhOH to be converted back to 1a with concomitant H2 formation, suggesting a potential for hydrogen storage through the fluxional exchange between face-capping and interstitial hydrides around the TTP scaffold.
Nakajima et al. (Mon,) studied this question.