Chambers Geoffrey M, Johnson Samantha I, Raugei Simone, Bullock R Morris
Center for Molecular Electrocatalysis , Pacific Northwest National Laboratory , Richland , Washington 99352 , USA . Email:
Chem Sci. 2018 Nov 23;10(5):1410-1418. doi: 10.1039/c8sc04239j. eCollection 2019 Feb 7.
Counterions can play an active role in chemical reactivity, modulating reaction pathways, energetics and selectivity. We investigated the tautomeric equilibrium resulting from protonation of Fe(PNP)(CO) (PNP = (EtPCH)NMe) at Fe or N. Protonation of Fe(PNP)(CO) by [(EtO)H][B(CF)] occurs at the metal to give the iron hydride [Fe(PNP)(CO)H][B(CF)]. In contrast, treatment with HBF·OEt gives protonation at the iron and at the pendant amine. Both the FeH and NH tautomers were characterized by single crystal X-ray diffraction. Addition of excess BF to the equilibrium mixture leads to the NH tautomer being exclusively observed, due to NH···F hydrogen bonding. A quantum chemical analysis of the bonding properties of these systems provided a quantification of hydrogen bonding of the NH to BF and to OTf. Treatment of Fe(PNP)(CO) with excess HOTf gives a dicationic complex where both the iron and nitrogen are protonated. Isomerization of the dicationic complex was studied by NOESY NMR spectroscopy.
抗衡离子可在化学反应性中发挥积极作用，调节反应途径、能量学和选择性。我们研究了Fe(PNP)(CO)（PNP = (EtPCH)NMe）在铁或氮处质子化所导致的互变异构平衡。[(EtO)H][B(CF)]使Fe(PNP)(CO)在金属处发生质子化，生成氢化铁[Fe(PNP)(CO)H][B(CF)]。相比之下，用HBF·OEt处理则导致铁和侧链胺处均发生质子化。FeH和NH互变异构体均通过单晶X射线衍射进行了表征。向平衡混合物中加入过量的BF会导致仅观察到NH互变异构体，这是由于NH···F氢键作用。对这些体系的键合性质进行量子化学分析，定量了NH与BF以及与OTf之间的氢键作用。用过量的HOTf处理Fe(PNP)(CO)会得到一种双阳离子配合物，其中铁和氮均被质子化。通过NOESY NMR光谱研究了双阳离子配合物的异构化。
