Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Am Chem Soc. 2012 Feb 15;134(6):3120-6. doi: 10.1021/ja2098468. Epub 2012 Jan 30.
We report the observation of a solvent-dependent spin state equilibrium in the 16-electron photoproduct CpCo(CO). Time-resolved infrared spectroscopy has been used to observe the concurrent formation of two distinct solvated monocarbonyl photoproducts, both of which arise from the same triplet CpCo(CO) precursor. Experiments in different solvent environments, combined with electronic structure theory calculations, allow us to assign the two solvated photoproducts to singlet and triplet CpCo(CO)(solvent) complexes. These results add to our previous picture of triplet reactivity for 16-electron organometallic photoproducts, in which triplets were not believed to interact strongly with solvent molecules. In the case of this photoproduct, it appears that spin crossover does not present a significant barrier to reactivity, and relative thermodynamic stabilities determine the spin state of the CpCo(CO) photoproduct in solution on the picosecond time scale. While the existence of transition metal complexes with two thermally accessible spin states is well-known, this is, to our knowledge, the first observation of a transient photoproduct that exhibits an equilibrium between two stable spin states, and also the first observed case in which a solvent has been able to coordinate as a token ligand to two spin states of the same photoproduct.
我们报告了在 16 电子光产物 CpCo(CO)中观察到溶剂依赖性自旋态平衡。时间分辨红外光谱已被用于观察两种不同溶剂化单羰基光产物的同时形成，这两种产物均来自相同的三重态 CpCo(CO)前体。在不同溶剂环境中的实验，结合电子结构理论计算，使我们能够将两种溶剂化光产物分配给单重态和三重态 CpCo(CO)(溶剂)配合物。这些结果增加了我们以前对 16 电子有机金属光产物的三重态反应性的认识，其中三重态被认为与溶剂分子没有强烈相互作用。在这种光产物的情况下，似乎自旋交叉对反应性没有显著的障碍，并且相对热力学稳定性决定了 CpCo(CO)光产物在溶液中的自旋态在皮秒时间尺度上。虽然具有两个热可及的自旋态的过渡金属配合物的存在是众所周知的，但这是我们首次观察到表现出两种稳定自旋态之间平衡的瞬态光产物，也是首次观察到溶剂能够作为同一光产物的两种自旋态的标记配体配位的情况。
