Department of Chemistry and Biochemistry, 5500 Campanile Drive, San Diego State University, San Diego, California 92182-1030, USA.
J Am Chem Soc. 2010 Jun 16;132(23):7919-34. doi: 10.1021/ja906712g.
Hydrogen bonding phenomena are explored using a combination of X-ray diffraction, NMR and IR spectroscopy, and DFT calculations. Three imidazolylphosphines R(2)PImH (ImH = imidazol-2-yl, R = t-butyl, i-propyl, phenyl, 1a-1c) and control phosphine (i-Pr)(2)PhP (1d) lacking an imidazole were used to make a series of complexes of the form Cp*Ir(L(1))(L(2))(phosphine). In addition, in order to suppress intermolecular interactions with either imidazole nitrogen, 1e, a di(isopropyl)imidazolyl analogue of 1b was made along with its doubly (15)N-labeled isotopomer to explore bonding interactions at each imidazole nitrogen. A modest enhancement of transfer hydrogenation rate was seen when an imidazolylphosphine ligand 1b was used. Dichloro complexes (L(1) = L(2) = Cl, 2a-2c,2e) showed intramolecular hydrogen bonding as revealed by four X-ray structures and various NMR and IR data. Significantly, hydride chloride complexes [L(1) = H, L(2) = Cl, 3a-3c and 3e-((15)N)(2)] showed stronger hydrogen bonding to chloride than hydride, though the solid-state structure of 3b evinced intramolecular Ir-H...H-N bonding reinforced by intermolecular N...H-N bonding between unhindered imidazoles. These results are compared to literature examples, which show variations in preferred hydrogen bonding to hydride, halide, CO, and NO ligands. Surprising differences were seen between the dichloro complex 2b with isopropyl groups on phosphorus, which appeared to exist as a mixture of two conformers, and related complex 2a with tert-butyl groups on phosphorus, which exists in chlorinated solvents as a mixture of conformer 2a-endo and chelate 5a-Cl, the product of ionization of one chloride ligand. This difference became apparent only through a series of experiments, especially (15)N chemical shift data from 2D (1)H-(15)N correlation. The results highlight the difficulty of characterizing hemilabile, bifunctional complexes and the importance of innocent ligand substituents in determining structure and dynamics.
氢键现象的研究采用了 X 射线衍射、NMR 和 IR 光谱以及 DFT 计算相结合的方法。三种咪唑基膦 R(2)PImH（ImH=咪唑-2-基，R=叔丁基、异丙基、苯基，1a-1c）和控制膦（i-Pr)(2)PhP（1d）缺乏咪唑，用于形成一系列形式为 Cp*Ir(L(1))(L(2))(膦)的配合物。此外，为了抑制与咪唑氮的分子间相互作用，合成了 1b 的二（异丙基）咪唑基类似物 1e 及其双（15）N 标记的同位素，以探索每个咪唑氮的键合相互作用。当使用咪唑基膦配体 1b 时，转移氢化速率略有提高。二氯配合物（L(1)=L(2)=Cl，2a-2c，2e）显示出分子内氢键，这通过四个 X 射线结构和各种 NMR 和 IR 数据揭示。重要的是，氯化氢配合物[L(1)=H，L(2)=Cl，3a-3c 和 3e-((15)N)(2)]显示出比氢化物更强的氢键与氯化物，尽管 3b 的固态结构显示出由未受阻咪唑之间的分子间 N...H-N 键合增强的 Ir-H...H-N 键合。这些结果与文献中的例子进行了比较，这些例子显示了对氢化物、卤化物、CO 和 NO 配体的首选氢键的变化。在磷上具有异丙基的二氯配合物 2b 与磷上具有叔丁基的相关配合物 2a 之间存在令人惊讶的差异，磷上具有异丙基的二氯配合物 2b 似乎存在两种构象的混合物，而磷上具有叔丁基的相关配合物 2a 存在于氯化溶剂中，作为构象 2a-endo 和螯合物 5a-Cl 的混合物，是一个氯化物配体的电离产物。只有通过一系列实验，特别是从 2D（1）H-(15)N 相关中获得的（15）N 化学位移数据，才能看出这种差异。结果突出了表征半配位、双功能配合物的困难以及无辜配体取代基在确定结构和动力学方面的重要性。
