Dehydrogenation of formic acid by Ir-bisMETAMORPhos complexes: experimental and computational insight into the role of a cooperative ligand.
Dehydrogenation of formic acid by Ir-bisMETAMORPhos complexes: experimental and computational insight into the role of a cooperative ligand.
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DOI：
10.1039/c4sc02555e
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发表时间：
2015-02-01
期刊：
影响因子：
8.4
通讯作者：
Reek JNH
中科院分区：
文献类型：
--
作者：
Oldenhof S;Lutz M;de Bruin B;Ivar van der Vlugt J;Reek JNH
本文报道了三种bisMETAMORPhos配体的铱配合物的合成。使用光谱和计算方法讨论了这些系统对HCOOH脱氢的活性以及配体在催化过程中的双重作用。报道了三个氧杂蒽基双METAMORPhos配体（La-Lc）的合成及其互变异构性质。这些双（磺酰胺基膦）与Ir（acac）（cod）的配位最初导致形成IrI（L H）物质（1a），其通过配体的形式氧化加成转化为IrIII（L）单氢化物络合物2a-c。该步骤的速率强烈地取决于所采用的配体。铱III配合物2a-c应用于甲酸的无碱脱氢，分别达到3090，877和1791 h-1的周转频率。通过~ 1H和~（31）P NMR谱和密度泛函理论计算研究了配体在脱氢反应机理中的双重作用。除了作为内部碱，bisMETAMORPhos还有助于甲酸在Ir配位球内的预组装，并有助于通过氢键稳定速率决定过渡态。
The synthesis of Ir-complexes with three bisMETAMORPhos ligands is reported. The activity of these systems towards HCOOH dehydrogenation and the dual role of the ligand during catalysis is discussed, using spectroscopic and computational methods. The synthesis and tautomeric nature of three xanthene-based bisMETAMORPhos ligands (La–Lc) is reported. Coordination of these bis(sulfonamidophosphines) to Ir(acac)(cod) initially leads to the formation of IrI(L H) species (1a), which convert via formal oxidative addition of the ligand to IrIII(L) monohydride complexes 2a–c. The rate for this step strongly depends on the ligand employed. IrIII complexes 2a–c were applied in the base-free dehydrogenation of formic acid, reaching turnover frequencies of 3090, 877 and 1791 h–1, respectively. The dual role of the ligand in the mechanism of the dehydrogenation reaction was studied by 1H and 31P NMR spectroscopy and DFT calculations. Besides functioning as an internal base, bisMETAMORPhos also assists in the pre-assembly of formic acid within the Ir-coordination sphere and aids in stabilizing the rate-determining transition state through hydrogen-bonding.
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