Huang Daria L, Beltrán-Suito Rodrigo, Thomsen Julianne M, Hashmi Sara M, Materna Kelly L, Sheehan Stafford W, Mercado Brandon Q, Brudvig Gary W, Crabtree Robert H
Department of Chemistry, Yale University , 225 Prospect Street, New Haven, Connecticut 06520, United States.
Department of Chemical and Environmental Engineering, Yale University , 9 Hillhouse Avenue, New Haven, Connecticut 06520, United States.
Inorg Chem. 2016 Mar 7;55(5):2427-35. doi: 10.1021/acs.inorgchem.5b02809. Epub 2016 Feb 22.
This paper introduces Ir(I)(CO)2(pyalc) (pyalc = (2-pyridyl)-2-propanoate) as an atom-efficient precursor for Ir-based homogeneous oxidation catalysis. This compound was chosen to simplify analysis of the water oxidation catalyst species formed by the previously reported CpIr(III)(pyalc)OH water oxidation precatalyst. Here, we present a comparative study on the chemical and catalytic properties of these two precursors. Previous studies show that oxidative activation of CpIr-based precursors with NaIO4 results in formation of a blue Ir(IV) species. This activation is concomitant with the loss of the placeholder Cp* ligand which oxidatively degrades to form acetic acid, iodate, and other obligatory byproducts. The activation process requires substantial amounts of primary oxidant, and the degradation products complicate analysis of the resulting Ir(IV) species. The species formed from oxidation of the Ir(CO)2(pyalc) precursor, on the other hand, lacks these degradation products (the CO ligands are easily lost upon oxidation) which allows for more detailed examination of the resulting Ir(pyalc) active species both catalytically and spectroscopically, although complete structural analysis is still elusive. Once Ir(CO)2(pyalc) is activated, the system requires acetic acid or acetate to prevent the formation of nanoparticles. Investigation of the activated bis-carbonyl complex also suggests several Ir(pyalc) isomers may exist in solution. By (1)H NMR, activated Ir(CO)2(pyalc) has fewer isomers than activated Cp*Ir complexes, allowing for advanced characterization. Future research in this direction is expected to contribute to a better structural understanding of the active species. A diol crystallization agent was needed for the structure determination of 3.
本文介绍了Ir(I)(CO)2(pyalc)（pyalc = (2 - 吡啶基)-2 - 丙酸酯）作为用于Ir基均相氧化催化的原子经济型前体。选择该化合物是为了简化对先前报道的CpIr(III)(pyalc)OH水氧化预催化剂形成的水氧化催化剂物种的分析。在此，我们对这两种前体的化学和催化性质进行了比较研究。先前的研究表明，用NaIO4对基于CpIr的前体进行氧化活化会导致形成蓝色的Ir(IV)物种。这种活化伴随着占位配体Cp的损失，其氧化降解形成乙酸、碘酸盐和其他必需的副产物。活化过程需要大量的初级氧化剂，并且降解产物使所得Ir(IV)物种的分析复杂化。另一方面，由Ir(CO)2(pyalc)前体氧化形成的物种缺乏这些降解产物（CO配体在氧化时容易丢失），这使得能够对所得的Ir(pyalc)活性物种进行更详细的催化和光谱研究，尽管完整的结构分析仍然难以实现。一旦Ir(CO)2(pyalc)被活化，该体系需要乙酸或乙酸盐来防止纳米颗粒的形成。对活化的双羰基配合物的研究还表明溶液中可能存在几种Ir(pyalc)异构体。通过1H NMR，活化的Ir(CO)2(pyalc)的异构体比活化的CpIr配合物少，便于进行高级表征。预计在这个方向上的未来研究将有助于更好地理解活性物种的结构。确定3的结构需要一种二醇结晶剂。
