MODELS OF CYTOCHROMES-B - ATTEMPTS TO CONTROL AXIAL LIGAND ORIENTATION WITH A HINDERED PORPHYRIN SYSTEM
MODELS OF CYTOCHROMES-B - ATTEMPTS TO CONTROL AXIAL LIGAND ORIENTATION WITH A HINDERED PORPHYRIN SYSTEM
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DOI：
10.1021/ic00007a041
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发表时间：
1991-04-03
影响因子：
4.6
通讯作者：
SCHEIDT, WR
中科院分区：
文献类型：
--
作者：
HATANO, K;SAFO, MK;SCHEIDT, WR
研究了咪唑配体与位阻卟啉衍生物（高氯酸）（四（2,6-二氯苯基）卟啉）铁（III），[Fe(T2,6Cl2PP)(OClO3)]的相互作用。 对 1-乙烯基-、1-甲基-和 2-甲基咪唑的逐步配体结合常数的测量得出的 log beta'-2 值分别为 7.41、5.16 和 7.12。 这些值清楚地表明八个邻氯基团不会阻碍轴向咪唑配体的结合。 报道了双(1-乙烯基咪唑)铁(III)衍生物的制备。 人们发现这种六配位低自旋配合物在固态下显示出不寻常的电子顺磁共振光谱，其中在 7 K 处观察到“正常菱形”和“大 g(max)”EPR 信号。冷冻溶液光谱仅显示菱形信号。 在 122 +/- 3 K 下测定的晶体结构显示出轴向咪唑的两种不同相对取向：“平行”和“垂直”。 观察到的垂直方向是轴向咪唑靠近相邻 Fe-N(p) 键的方向。 两种不同的相对咪唑取向显然是由晶体堆积和不超过 1/4 的轴向配体被杂质咪唑取代的影响造成的。 对垂直物种的 EPR 数据的分析表明，与咪唑平面平分卟啉氮轴的复合物相比，咪唑平面与卟啉氮轴的近似重叠导致了更小的导出菱形 (V/DELTA)（[Fe(TPP)(2-MeHIm)2]+ 就是这种情况，J. Am. Chem. Soc. 1986, 108, 5288）。 平均赤道 Fe-N(p) 键距为 1.978 (6) 埃，而轴向距离为 1.968 (4) 和 1.976 (4) 埃。 porphinato 核心具有适度的 D2d 褶边构象。 [Fe(T2,6Cl2PP)(1-VinIm)2]ClO4 的晶体数据：a = 12.288 (4) 埃，b = 21.402 (8) 埃，c = 20.975 (6) 埃，β = 105.42 (2) 度，单斜晶系，空间群 P2(1)/n，V = 5317.8 埃3，Z = 4,6642 个观测数据，R1 = 0.061，R2 = 0.073。
The interaction of imidazole ligands with the sterically hindered pophyrin derivative (perchlorato)(tetrakis(2,6-dichlorophenyl)porphinato)iron(III), [Fe(T2,6Cl2PP)(OClO3)], has been investigated. Measurements of stepwise ligand binding constants for 1-vinyl-, 1-methyl-, and 2-methylimidazole yield derived values of log beta'-2 of 7.41, 5.16, and 7.12, respectively. These values clearly show that the eight o-chloro groups do not hinder the binding of the axial imidazole ligands. The preparation of the bis(1-vinylimidazole)iron(III) derivative is reported. This six-coordinate low-spin complex is found to display an unusual electron paramagnetic resonance spectrum in the solid state where both a "normal rhombic" and a "large g(max)" EPR signal are observed at 7 K. The frozen solution spectrum shows only the rhombic signal. The crystal structure, determined at 122 +/- 3 K, shows two different relative orientations of the axial imidazoles: "parallel" and "perpendicular". The observed perpendicular orientation is the one in which the axial imidazoles lie close to adjacent Fe-N(p) bonds. The two different relative imidazole orientations apparently result from the effects of crystal packing and the replacement of no more than 1/4 of the axial ligands by an impurity imidazole. Analysis of the EPR data for the perpendicular species suggests that the approximate eclipsing of imidazole planes with porphyrin nitrogen axes leads to a much smaller derived rhombicity (V/DELTA) compared to the complex with imidazole planes bisecting the porphyrin nitrogen axes (which was the case for [Fe(TPP)(2-MeHIm)2]+, J. Am. Chem. Soc. 1986, 108, 5288). The average equatorial Fe-N(p) bond distance is 1.978 (6) angstrom while the axial distances are 1.968 (4) and 1.976 (4) angstrom. The porphinato core has a modest D2d ruffled conformation. Crystal data for [Fe(T2,6Cl2PP)(1-VinIm)2]ClO4: a = 12.288 (4) angstrom, b = 21.402 (8) angstrom, c = 20.975 (6) angstrom, beta = 105.42 (2)-degrees, monoclinic, space group P2(1)/n, V = 5317.8 angstrom-3, Z = 4,6642 observed data, R1 = 0.061, R2 = 0.073.