Synthesis, Structural Characterization, and Gas-Phase Unimolecular Reactivity of Bis(diphenylphosphino)amino Copper Hydride Nanoclusters [Cu<sub>3</sub>(X)(μ<sub>3</sub>‑H)((PPh<sub>2</sub>)<sub>2</sub>NH)<sub>3</sub>](BF<sub>4</sub>), Where X = μ<sub>2</sub>‑Cl and μ<sub>3</sub>‑BH<sub>4</sub>
收藏资源简介：
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(μ2-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)(LMe)3]+ suggest that BH3 loss produces the hitherto elusive [Cu3(μ3-H)(μ2-H)(LMe)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]+.
本研究采用电喷雾电离质谱（electrospray ionization mass spectrometry, ESI-MS）对由四(乙腈)合铜(I)四氟硼酸盐[Cu(MeCN)₄(BF₄)]、双(二苯基膦基)胺（bis(diphenylphosphino)amine, dppa = (Ph₂P)₂NH = L）与硼氢化钠以1:1:20比例混合的乙腈溶液中生成的阳离子铜团簇类型进行了调研，结果观测到一个主要峰。结合精确质量与同位素分布分析，该峰被归属为[Cu₃(BH₄)(H)(L)₃]⁺。这一发现推动了后续合成工作，最终分离得到了dppa配位的三核氢化铜纳米团簇[Cu₃(μ₂-Cl)(μ₃-H)(L)₃](BF₄)与[Cu₃(μ₃-BH₄)(μ₃-H)(L)₃](BF₄)，并通过高分辨ESI-MS、X射线晶体学、核磁共振（nuclear magnetic resonance, NMR）及红外（infrared, IR）光谱对其结构进行了表征。X射线晶体结构显示该阳离子具有共同的结构特征：三个铜(I)离子形成平面三核Cu₃几何构型，其底面由μ₃-氢化物配位，且被三个dppa配体环绕。对[Cu₃(μ₂-Cl)(μ₃-H)(L)₃](BF₄)与[Cu₃(μ₃-BH₄)(μ₃-H)(L)₃](BF₄)进行ESI-MS分析，分别得到了[Cu₃(μ₂-Cl)(μ₃-H)(L)₃]⁺与[Cu₃(μ₃-BH₄)(μ₃-H)(L)₃]⁺。本研究采用多级串联质谱结合碰撞诱导解离（collision-induced dissociation, CID）条件，考察了上述阳离子的单分子气相离子化学行为。两种阳离子的CID过程均通过配体解离生成[Cu₃(μ₃-H)(X)(L)₂]⁺，当X为BH₄时，该路径与BH₃解离过程存在竞争。对[Cu₃(μ₃-BH₄)(μ₃-H)(LMe)₃]⁺碎片化过程的密度泛函理论（density functional theory, DFT）计算表明，BH₃解离会生成迄今尚未被观测到的[Cu₃(μ₃-H)(μ₂-H)(LMe)₃]⁺，该离子可进一步通过失去H₂发生碎片化。对氘标记团簇[Cu₃(μ₃-D)(μ₃-BD₄)(L)₃]⁺的CID实验显示，配体解离与BD₃解离这两条竞争路径分别生成初级产物[Cu₃(μ₃-BD₄)(μ₃-D)(L)₂]⁺与[Cu₃(D)₂(L)₃]⁺，二者后续可通过进一步失去BD₃或配体生成[Cu₃(D)₂(L)₂]⁺。该离子中的配位氢化物会被活化以消除D₂，最终得到[Cu₃(L)₂]⁺。失去HD与2HD的过程为次要反应通道，这与DFT预测的生成[Cu₃(D)(L)(L-H)]⁺及[Cu₃(L-H)₂]⁺所需的吸热焓更高的结果一致。
