Activation barriers to meso-aryl group rotation in titanyl tetraaryltetrapyrroles. An investigation of the out-of-plane flexibility of hydroporphyrins.
Activation barriers to meso-aryl group rotation in titanyl tetraaryltetrapyrroles. An investigation of the out-of-plane flexibility of hydroporphyrins.
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DOI：
10.1021/ic010936o
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发表时间：
2002-01
影响因子：
4.6
通讯作者：
A. M. Stolzenberg;G. S. Haymond
中科院分区：
文献类型：
--
作者：
A. M. Stolzenberg;G. S. Haymond
合成并表征了meso-四甲苯基和meso-四（3，5-二甲苯基）氢化卟啉的游离碱和钛氧（Ti（IV）O）配合物。氢化卟啉与钛的金属化是通过氢化卟啉的锂盐与TiCl（4）的反应实现的。其他方法用于金属化卟啉与钛需要苛刻的反应条件，并导致大量的大环氧化脱氢时，应用于氢卟啉。钛氧基区分大环的两个面，并因此区分内消旋芳基的两个侧面，其几乎垂直于大环平面倾斜。由于芳基旋转，在升高的温度下，非等效邻位质子和非等效Meta质子的（1）H NMR信号在NMR时间标度上平均。对位取代和间二取代的钛氧基氢化卟啉配合物和相关的钛氧基卟啉配合物中芳基旋转的活化势垒从变温NMR光谱确定，范围从15.6至18.4千卡/摩尔。在二氢卟酚化合物中，位于吡咯和吡咯啉（还原）环之间的芳基的旋转势垒大于位于两个吡咯环之间的芳基的旋转势垒。在具有不同大环饱和度水平的复合物中的势垒的比较表明，吡咯啉环附近的芳基基团的势垒的增加不能仅仅归因于吡咯啉β-CH（2）基团相对于吡咯β-CH基团的空间体积的增加。在氢卟啉中的中位碳的柔性和电子环境的变化也可能有贡献。间位-二取代芳基的旋转位垒比对位取代芳基的旋转位垒高，随着取代基的大小和质量而增加。
The free-base and titanyl (Ti(IV)O) complexes of meso-tetratolyl- and meso-tetra(3,5-xylyl)hydroporphyrins were synthesized and characterized. Metalation of the hydroporphyrins with titanium was achieved by reaction of the lithium salts of the hydroporphyrin with TiCl(4). Other methods used to metalate porphyrins with titanium required harsher reaction conditions and led to substantial oxidative dehydrogenation of the macrocycle when applied to hydroporphyrins. The titanyl group differentiates the two faces of the macrocycle and consequently the two sides of the meso-aryl groups, which are tilted nearly perpendicular to the macrocycle plane. The (1)H NMR signals for the nonequivalent ortho protons and nonequivalent meta protons averaged on the NMR time scale at elevated temperatures due to aryl group rotation. Activation barriers for aryl group rotation in the para-substituted and meta-disubstituted titanyl hydroporphyrin complexes and in related titanyl porphyrin complexes were determined from variable-temperature NMR spectra and ranged from 15.6 to 18.4 kcal/mol. In chlorin compounds, barriers for rotation of aryl groups located between a pyrrole and a pyrroline (reduced) ring are greater than those of aryl groups located between two pyrrole rings. Comparisons of barriers in complexes with different macrocycle saturation levels show that the increased barriers for aryl groups adjacent to pyrroline rings cannot be attributed solely to the increased steric bulk of the pyrroline beta-CH(2) group relative to the pyrrole beta-CH group. Variations in flexibility and electronic environments at meso carbons in the hydroporphyrins may also contribute. Rotation barriers for meta-disubstituted aryl groups, which are higher than those for para-substituted aryl groups, increase with the size and mass of the substituent.