Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall, University of Notre Dame, Notre Dame, Indiana 46556-5670, United States.
Inorg Chem. 2012 Feb 6;51(3):1251-60. doi: 10.1021/ic202764j. Epub 2012 Jan 19.
Catecholates and 2-amidophenoxides are prototypical "noninnocent" ligands which can form metal complexes where the ligands are best described as being in the monoanionic (imino)semiquinone or neutral (imino)quinone oxidation state instead of their closed-shell dianionic form. Through a comprehensive analysis of structural data available for compounds with these ligands in unambiguous oxidation states (109 amidophenolates, 259 catecholates), the well-known structural changes in the ligands with oxidation state can be quantified. Using these correlations, an empirical "metrical oxidation state" (MOS) which gives a continuous measure of the apparent oxidation state of the ligand can be determined based on least-squares fitting of its C-C, C-O, and C-N bond lengths to this single parameter (a simple procedure for doing so is provided via a spreadsheet in the Supporting Information). High-valent d(0) metal complexes, particularly those of vanadium(V) and molybdenum(VI), have ligands with unexpectedly positive, and generally nonintegral, MOS values. The structural effects in these complexes are attributed not to electron transfer, but rather to amidophenoxide- or catecholate-to-metal π bonding, an interpretation supported by the systematic variation of the MOS values as a function of the degree of competition with the other π-donating groups in the structures.
儿茶酚和 2-苯并异噁唑啉是典型的“非中性”配体，可形成金属配合物，其中配体最好被描述为单阴离子（亚氨基）半醌或中性（亚氨基）醌氧化态，而不是其闭壳层二阴离子形式。通过对具有这些配体的化合物在明确氧化态下的结构数据（109 个苯并异噁唑啉配体，259 个儿茶酚配体）进行全面分析，可以量化配体氧化态的已知结构变化。使用这些相关性，可以根据其 C-C、C-O 和 C-N 键长与该单一参数（通过支持信息中的电子表格提供了一种简单的执行此操作的方法）的最小二乘拟合，确定连续测量配体表观氧化态的经验“计量氧化态”（MOS）。高价 d(0)金属配合物，特别是钒 (V) 和钼 (VI) 的配合物，其配体具有出人意料的正、通常是非整数的 MOS 值。这些配合物中的结构效应不是归因于电子转移，而是归因于苯并异噁唑啉或儿茶酚与金属的 π 键合，这一解释得到了 MOS 值作为结构中其他 π 供体基团竞争程度的函数的系统变化的支持。
