Synthesis, Structural Characterization, and Gas-Phase Unimolecular Reactivity of Bis(diphenylphosphino)amino Copper Hydride Nanoclusters [Cu₃(X)(μ₃‑H)((PPh₂)₂NH)₃](BF₄), Where X = μ₂‑Cl and μ₃‑BH₄

An electrospray ionization mass spectrometry (ESI-MS) survey of the types of cationic copper clusters formed from an acetonitrile solution containing a 1:1:20 mixture of tetrakis­(acetonitrile)­copper­(I) tetrafluoroborate [Cu­(MeCN)₄(BF₄)], bis­(diphenylphosphino)­amine (dppa = (Ph₂P)₂NH = L), and NaBH₄ revealed a major peak, which based on both the accurate masses and isotope distribution was assigned as [Cu₃(BH₄)­(H)­(L)₃]⁺. This prompted synthetic efforts resulting in isolation of the dppa ligated trinuclear copper hydride nanoclusters, [Cu₃(μ₂-Cl)­(μ₃-H)­(L)₃]­(BF₄) and [Cu₃(μ₃-BH₄)­(μ₃-H)­(L)₃]­(BF₄), which were subsequently structurally characterized using high resolution ESI-MS, X-ray crystallography, NMR, and IR spectroscopy. The X-ray structures reveal a common structural feature of the cation, in which the three copper­(I) ions adopt a planar trinuclear Cu₃ geometry coordinated on the bottom face by a μ₃-hydride and surrounded by three dppa ligands. ESI-MS of [Cu₃(<i>μ</i>₂-Cl)­(μ₃-H)­(L)₃]­(BF₄) and [Cu₃(μ₃-BH₄)­(μ₃-H)­(L)₃]­(BF₄) produces [Cu₃(μ₂-Cl)­(μ₃-H)­(L)₃]⁺ and [Cu₃(μ₃-BH₄)­(μ₃-H)­(L)₃]⁺. The unimolecular gas-phase ion chemistry of these cations was examined under multistage tandem mass spectrometry conditions using collision-induced dissociation (CID). CID of both cations proceeds via ligand loss to give [Cu₃(μ₃-H)­(X)­(L)₂]⁺, which is in competition with BH₃ loss in the case of X = BH₄. DFT calculations on the fragmentation of [Cu₃(μ₃-BH₄)­(μ₃-H)­(L^Me)₃]⁺ suggest that BH₃ loss produces the hitherto elusive [Cu₃(μ₃-H)­(μ₂<i>-</i>H)­(L^Me)₃]⁺, which undergoes further fragmentation via H₂ loss. CID of the deuterium labeled cluster [Cu₃(μ₃-D)­(μ₃-BD₄)­(L)₃]⁺ reveals that the competing losses of ligand and BD₃ yield [Cu₃(μ₃-BD₄)­(μ₃-D)­(L)₂]⁺ and [Cu₃(D)₂(L)₃]⁺ as primary products, which subsequently fragment via further losses of BD₃ or a ligand to give [Cu₃(D)₂(L)₂]⁺. The coordinated hydrides in the latter ion are activated toward elimination of D₂ to give [Cu₃(L)₂]⁺. Loss of HD and 2HD are minor channels, consistent with higher DFT predicted endothermicities to form [Cu₃(D)­(L)­(L-H)]⁺ and [Cu₃(L-H)₂]<sup>+