Substituent control of hydrogen bonding in palladium(II)-pyrazole complexes.
Substituent control of hydrogen bonding in palladium(II)-pyrazole complexes.
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钯(II)-吡唑配合物中氢键的取代基控制。
DOI：
10.1021/ic026104n
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发表时间：
2003
影响因子：
4.6
通讯作者：
Lupe H. Mejorado
中科院分区：
文献类型：
--
作者：
D. Grotjahn;S. Van;D. Combs;Daniel A. Lev;C. Schneider;C. Incarvito;Kim;G. Rossi;A. Rheingold;M. Rideout;C. Meyer;G. Hernandez;Lupe H. Mejorado
使用吡唑 C-3 和 C-5 处具有两个不同基团的配体研究了吡唑配合物中 N-H 基团的分子间和分子内氢键。在C-5处，存在诸如甲基、异丙基、苯基或叔丁基的基团。在 C-3 处，侧链 L-CH(2)- 和 L-CH(2)CH(2)-（L = 硫醚或膦）确保通过侧链原子 L 和最靠近侧链的吡唑氮形成顺式二氯钯 (II) 片段的螯合物。配体的重要性在于，通过将连接侧链放置在环碳（C-3）上，而不是环氮上，未与金属结合的环氮及其连接的质子可用于氢键合。根据需要，通过 X 射线衍射检查的七种螯合配合物均显示吡唑 N-H 和顺式位置的氯化物配体之间存在分子内氢键。然而，此外，分子间氢键可以通过C-5处的取代基来控制：C-5处具有甲基或没有取代基的配合物显示出显着的分子间氢键相互作用，而通过在C-5处放置叔丁基可以完全避免这种相互作用。据估计，乙腈溶液中两种络合物的酸度比咪唑鎓或三乙铵离子的酸度更接近吡啶鎓离子的酸度。
Inter- and intramolecular hydrogen bonding of an N-H group in pyrazole complexes was studied using ligands with two different groups at pyrazole C-3 and C-5. At C-5, groups such as methyl, i-propyl, phenyl, or tert-butyl were present. At C-3, side chains L-CH(2)- and L-CH(2)CH(2)- (L = thioether or phosphine) ensured formation of chelates to a cis-dichloropalladium(II) fragment through side-chain atom L and the pyrazole nitrogen closest to the side chain. The significance of the ligands is that by placing a ligating side chain on a ring carbon (C-3), rather than on a ring nitrogen, the ring nitrogen not bound to the metal and its attached proton are available for hydrogen bonding. As desired, seven chelate complexes examined by X-ray diffraction all showed intramolecular hydrogen bonding between the pyrazole N-H and a chloride ligand in the cis position. In addition, however, intermolecular hydrogen bonding could be controlled by the substituent at C-5: complexes with either a methyl at C-5 or no substituent there showed significant intermolecular hydrogen bonding interactions, which were completely avoided by placing a tert-butyl group at C-5. The acidity of two complexes in acetonitrile solutions was estimated to be closer to that of pyridinium ion than those of imidazolium or triethylammonium ions.