Importance of the Reactant-State Potentials of Chromium(V)?Oxo Complexes to Determine the Reactivity in Hydrogen-Atom Transfer Reactions
Importance of the Reactant-State Potentials of Chromium(V)?Oxo Complexes to Determine the Reactivity in Hydrogen-Atom Transfer Reactions
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铬(V)?氧配合物的反应物态电势对于确定氢原子转移反应的反应性的重要性
DOI：
10.1021/acs.inorgchem.8b02453
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发表时间：
2018
影响因子：
4.6
通讯作者：
Kojima Takahiko
中科院分区：
文献类型：
--
作者：
Kotani Hiroaki;Kaida Suzue;Ishizuka Tomoya;Mieda Kaoru;Sakaguchi Miyuki;Ogura Takashi;Shiota Yoshihito;Yoshizawa Kazunari;Kojima Takahiko
合成了一种新的铬(V)-氧配合物[CrV(O)(6-CoO-Py-Tacn)]2+(1；6-CoO-py-Tacn=1-(6-carboxylato-2-pyridylmethyl)-4，7-dimethyl-1，4，7-triazacyclononane)，)，并通过与已报道的CrV(O)配合物[CrV(O)(6-CoO-Tpa)]2+(2；6-COO--tpa=N，N-bis(2-pyridylmethyl)-N-(6-carboxylato-2-pyridylmethyl)amine).在铬-氧键的共振拉曼散射(ν分别为911 cm-1和951 cm-1)和还原电位(0.73V vsSce和1.23V)上观察到这两个CrV(O)络合物的明显差异，这种差异应该来自于配体与氧配体、叔胺基团和吡啶氮的结合。当我们以9，10-二氢菲为底物时，1的二级速率常数(K)比2小4000倍。两个配合物相对于C-H键的解离能(BDEs)的归一化K值在几个底物上裂解的图显示出一对平行线，斜率分别为1的−0.91和2的−0.62，表明两个配合物的HAT反应通过几乎相同的过渡态进行。从CrIV(OH)/CrV(O)(85~87kcal·mol~(-1)(1)和92~94kcal·mol~(-1)(2))和DHA HAT反应的活化势垒(Ea=7.9kcal~(-1)(1)和Ea=4.8kcal·mol~(-1)(2))来看，CrV(O)络合物在HAT反应中的反应活性取决于反应态的能级，而不是产物态。
A new chromium(V)–oxo complex, [CrV(O)(6-COO–-py-tacn)]2+(1; 6-COO–-py-tacn = 1-(6-carboxylato-2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane), was synthesized and characterized to evaluate the reactivity of CrV(O) complexes in a hydrogen-atom transfer (HAT) reaction by comparing it with that of a previously reported CrV(O) complex, [CrV(O)(6-COO–-tpa)]2+(2; 6-COO–-tpa =N,N-bis(2-pyridylmethyl)-N-(6-carboxylato-2-pyridylmethyl)amine). Definitive differences of these two CrV(O) complexes were observed in resonance Raman scatterings of the Cr–O bond (ν = 911 cm–1for1and 951 cm–1for2) and the reduction potential (0.73 V vs SCE for1and 1.23 V for2); this difference should be derived from that of the ligand bound at thetransposition to the oxo ligand, a tertiary amino group in1, and a pyridine nitrogen in2. When we employed 9,10-dihydroanthracene as a substrate, the second-order rate constant (k) of1was 4000 times smaller than that of2. Plots of normalizedkvalues for both complexes relative to bond dissociation energies (BDEs) of C–H bonds to be cleaved in several substrates showed a pair of parallel lines with slopes of −0.91 for1and −0.62 for2, indicating that the HAT reactions by the two complexes proceed via almost the same transition states. Judging from estimated BDEs of CrIV(OH)/CrV(O) (85–87 kcal mol–1for1and 92–94 kcal mol–1for2) and the activation barrier in the HAT reaction of DHA (Ea= 7.9 kcal mol–1for1andEa= 4.8 kcal mol–1for2), the reactivity of CrV(O) complexes in HAT reactions depends on the energy level of the reactant state rather than the product state.