Electrochemical behavior of a Rh(pentamethylcyclopentadienyl) complex bearing an NAD+/NADH-functionalized ligand
Electrochemical behavior of a Rh(pentamethylcyclopentadienyl) complex bearing an NAD+/NADH-functionalized ligand
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带有 NAD /NADH 功能化配体的 Rh（五甲基环戊二烯基）络合物的电化学行为
DOI：
10.1039/c7dt04594h
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Koji Tanaka
中科院分区：
文献类型：
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作者：
Katsuaki Kobayashi;Take-aki Koizumi;Debashis Ghosh;Takashi Kajiwara;Susumu Kitagawa;Koji Tanaka
合成了一种带有NAD+/NADH功能化配体[RhCp*（pbn）Cl]Cl（[1]Cl，pbn =（2-（2-吡啶基）苯并[B]-1，5-萘啶））的RhCp*（Cp* =五甲基吡啶）配合物。[1]Cl在CH 3CN中的循环伏安图在E1/2 = −0.58和−1.53 V（相对于饱和甘汞电极（SCE））处显示出两个可逆的氧化还原波，分别对应于RhIII/RhI和pbn/pbn stec −氧化还原电对。在溶液中加入乙酸，[1]Cl在-0.62 V下发生质子耦合的双电子还原，由此选择性地生成[RhCp*（pbnHH）Cl]+，可能是通过从RhIII-氢化物中间体到pbn配体的氢化物转移。络合物[1]Cl在酸性条件下是稳定的，而Cp* 部分的甲基质子在碱性条件下解离。由此产生的阴离子亚甲基攻击pbn的游离吡啶的帕拉碳，伴随着配体的氮原子的质子化。因此，用碱处理[1]Cl选择性地产生环状络合物[1CH]Cl，其具有还原的pbn框架（pbnCH）。[1CH]Cl与PhCOO-通过氢键形成1：1加合物。 据报道，由Ru-pbnHH骨架和RCOO−（R = CH 3，C6 H5）形成的类似加合物在Ru-pbn的伴随再生下与CO2反应生成HCOO−。然而，[1CH]Cl与PhCOO-的加合物缺乏这种氢化物供体能力，因为[1CH]Cl分子结构中的位阻阻碍了氢化物转移。
A RhCp* (Cp* = pentamethylcyclopentadienyl) complex bearing an NAD+/NADH-functionalized ligand, [RhCp*(pbn)Cl]Cl ([1]Cl, pbn = (2-(2-pyridyl)benzo[b]-1,5-naphthyridine)), was synthesized. The cyclic voltammogram of [1]Cl in CH3CN shows two reversible redox waves at E1/2 = −0.58 and −1.53 V (vs. the saturated calomel electrode (SCE)), which correspond to the RhIII/RhI and pbn/pbn˙− redox couples, respectively. The addition of acetic acid to the solution afforded the proton-coupled two-electron reduction of [1]Cl at −0.62 V, from which [RhCp*(pbnHH)Cl]+ was selectively generated, probably via a hydride transfer from a RhIII–hydride intermediate to the pbn ligand. Complex [1]Cl is stable under acidic conditions, whereas a methyl proton of the Cp* moiety dissociates under basic conditions. The resulting anionic methylene group attacks the para carbon of the free pyridine of pbn, accompanied by protonation of the nitrogen atom of the ligand. As a result, treatment of [1]Cl with a base produces selectively the cyclic complex [1CH]Cl, which bears a reduced pbn framework (pbnCH). [1CH]Cl forms 1 : 1 adducts with PhCOO−via hydrogen bonding. A similar adduct, formed by a Ru–pbnHH scaffold and RCOO− (R = CH3, C6H5), has been reported to react with CO2 to produce HCOO− under concomitant regeneration of Ru–pbn. The adduct of [1CH]Cl with PhCOO−, however, lacks such hydride-donor ability, due to a steric barrier in the molecular structure of [1CH]Cl, which hampers the hydride transfer.