[Fe (IV) O (TBC) CH3CN) ]2+:铁 (IV) 氧物种的比较反应性与受限制的赤道环结合的环结合
Samuel A Wilson1, Junying Chen, Seungwoo Hong
1Department of Chemistry, Stanford University, Stanford, California 94305, USA.
Journal of the American Chemical Society
|June 20, 2012
概括
与铁复合物进行比较,大型基团在一个 (TBC) 上的激活障碍对于原子抽象和氧转移反应明显较低,与甲基替代模拟物 (TMC) 相比. 这种反应性差异源于影响自旋状态和过渡状态几何的固态效应.
科学领域:
- 无机化学 无机化学 有机化学
- 有机金属化学 有机金属化学
- 计算化学计算化学
背景情况:
- 铁氧复合物在生物和化学氧化过程中至关重要.
- 了解连接体对铁氧活性的影响,是催化剂设计的关键.
- 金属中心周围的绝缘体积可以大大改变反应路径.
研究的目的:
- 为了比较[Fe(IV) O ((TBC) ((CH3CN) ]2+和[Fe(IV) O ((TMC) ((CH3CN) ]2+在H原子抽象和氧转移反应中的反应性.
- 阐明控制观察到的反应性差异的结构和电子因素.
- 来自X射线吸收光谱学的结构见解与密度函数理论的反应性预测进行相关联.
主要方法:
- 用四基- (TBC) 和四甲基- (TMC) 环联体合成和表征铁氧复合物.
- 射线吸收光谱 (XAS) 探测结构和电子特性.
- 密度函数理论 (DFT) 计算以调查反应机制,过渡状态和激活障碍.
- 动力学研究来评估原子抽象和氧转移速率.
主要成果:
- 这两种S=1基态都表现出高激活障碍H原子抽象由于硬质障碍和首选的π攻击.
- 在S=2表面的H原子抽象显示出明显较低的障碍 (~9 kcal/mol vs ~25 kcal/mol) 由于降低了固体相互作用和有利的σ攻击.
- [Fe (IV) O (TBC) CH3CN) ]2+受益于可访问的S=2兴奋状态,从而在H原子抽取和氧转移反应中降低了障碍.
- 氧转移反应由S=2路径促进,涉及连续的电子转移和扭曲的过渡状态,对TBC复合体有改善的轨道重叠.
结论:
- 硬质体的TBC连接体,特别是基组,在调节铁氧复合物的反应性方面发挥着至关重要的作用.
- 在H原子抽象和氧转移反应中,更高的自旋状态 (S=2) 的可访问性对于降低激活障碍至关重要.
- 由庞大的配体引起的结构扭曲增强了轨道重叠和加速氧转移率,为设计更有效的氧化催化剂提供了洞察力.
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