Planar-Locked Ru-PNN Catalysts in 1-Phenylethanol Dehydrogenation
Planar-Locked Ru-PNN Catalysts in 1-Phenylethanol Dehydrogenation
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DOI：
10.1021/acs.organomet.0c00327
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发表时间：
2020-10-26
期刊：
影响因子：
2.8
通讯作者：
Lacy, David C.
中科院分区：
文献类型：
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作者：
Fanara, Paul M.;MacMillan, Samantha N.;Lacy, David C.
一般形式 [{PNN}Ru(H)(Cl)(CO)] 的 Ru-PNN 钳形催化剂可以通过内球和外球机制使醇脱氢，但确定首选路径具有挑战性。为了应对这一挑战，合成了以下不能形成关键内球过渡态和中间体的平面锁定喹啉基PNN配体：2-((二叔丁基膦基)甲基)-N,N-二乙基喹啉-8-胺(QNP(tBu))、2-((二异丙基膦基)甲基)-N,N-二乙基喹啉-8-胺(QNP(iPr))和2-((二苯基膦基)甲基)-N,N-二乙基喹啉-8-胺(QNP(Ph))。除了喹啉衍生的配体之外，我们还制备了异喹啉 PNN 配体 N-((1-((二叔丁基膦基)甲基)异喹啉-3-基)甲基)-N-乙基乙胺 (IsoQNP) 和两种已知的甲基吡啶和二甲基吡啶衍生的配体 2-((二叔丁基膦基)甲基)吡啶 (PicP) 和2-((二叔丁基膦基)甲基)-6-甲基吡啶(LutP)。这六种配体与 Ru(II) 离子配位，制备了六种新的络合物，其通式为 [{L}Ru(H)(Cl)(CO)]，类似于 Milstein 的 PNN 催化剂前体 (1PyCl)。新配合物的X射线结构、NMR、UV-vis和FTIR光谱性质与母体配合物1PyCl相似，可用于催化1-苯乙醇无受体和转移脱氢。比较结果表明1Py优于其他催化剂。计算了 1Py 和平面锁定催化剂的 DFT 反应曲线。结果表明，1Py 可以进入较低能量的内球路径，而平面锁定催化剂只能通过高能量的外球机制进行，甚至可能被困在不反应的醇盐汇中。
Ru-PNN pincer catalysts of the general form [{PNN}Ru(H)(Cl)(CO)] can dehydrogenate alcohols through inner- and outer-sphere mechanisms, but determining the favored path is challenging. To address this challenge, the following planar-locked quinoline-based PNN ligands, which cannot form key inner-sphere transition states and intermediates, were synthesized: 2-((ditertbutylphosphaneyl)methyl)-N,N-diethylquinolin-8-amine (QNP(tBu)), 2-((diisopropylphosphaneyl)methyl)-N,N-diethylquinolin-8-amine (QNP(iPr)), and 2-((diphenylphosphaneyl)methyl)-N,N-diethylquinolin-8-amine (QNP(Ph)). In addition to the quinoline-derived ligands, we also prepared the isoquinoline PNN ligand N-((1-((ditert-butylphosphaneyl)methyl)isoquinolin-3-yl)methyl)-N-ethylethanamine (IsoQNP) and two known picoline- and lutidine-derived ligands 2-((ditert-butylphosphaneyl)methyl)pyridine (PicP) and 2-((ditert-butylphosphaneyl)methyl)-6-methylpyridine (LutP). These six ligands were coordinated to Ru(II) ions to prepare six new complexes of the general formulation [{L}Ru(H)(Cl)(CO)] analogous to Milstein's PNN catalyst precursor (1PyCl). The X-ray structural, NMR, UV-vis, and FTIR spectroscopic properties of the new complexes are similar to parent complex 1PyCl and were used in catalytic 1-phenylethanol acceptor-less and transfer dehydrogenation. The comparative results demonstrate that 1Py outperforms the other catalysts. DFT reaction profiles were computed for 1Py and the planar-locked catalysts. The results suggest that 1Py has access to a lower-energy inner-sphere path, whereas the planar-locked catalysts can only proceed through a high-energy outer-sphere mechanism and may even get trapped in unreactive alkoxide sinks.