Structures and Kinetics of Nickel(II) and Copper(II) Macrocyclic Complexes

• Main Authors: Yung-Chan Lin, 林永展
• Other Authors: Chung-Sun Chung
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/946je8

博士 === 國立清華大學 === 化學系 === 92 === The tetraaza-macrocyclic ligands were synthesized by two methods. (1) The protecting group method reported by Richman and Atkins was used for the synthesis of isocyclam. (2) The general organic method with Michael addition reaction was employed to prepare 3-10-C-meso-Me8[14]dieneN4.2HClO4. The structures and components of these ligands were analyzed and identified by NMR, IR, UV-vis, mass, and X-ray studies. The complexes of Ni(II) and Cu(II) were synthesized by using Ni(ClO4)2.6H2O, Ni(OAc)2.4H2O, or Cu(ClO4)2.6H2O in hot methanol solution and recrystallized from water or acetonitrile. According to the results of NMR and X-ray studies, the structures of isomers, LB and LC, from reduction of 3-10-C-meso- Me8[14]dieneN4·2HClO4 and their complexes of Ni(II) and Cu(II) are indeed different from literature reports. We could not get the isomer LA following the experimental methods described in the published paper and in our work. The melting point of LB is greater than that of LC and the melting point of LA is anticipated to be higher than that of LB. The solubility of LB in organic solvent is less than that of LC, while that of LA is expected to be lower compared to LB. The 1H NMR spectrum of LB shows four methyl resonances for eight methyl groups suggesting that LB is a symmetric molecule whereas the isomer LC shows eight methyl resonances indicating that LC is an asymmetric molecule. The 13C NMR spectrum of LB displayed only nine peaks due to pairwise equivalence of carbon atoms. In contrast, isomer LC displayed eighteen peaks of corresponding to eighteen nonequivalent carbon atoms indicating the absence of symmetry in the molecule. We have studied the X-ray diffractional analysis of isomeric LB, LC and their transition metal complexes. (1) Crystal structure of 3,10-C-meso-5,12-C-meso-Me8[14]aneN4 (LB). The molecule is located at an inversion. This determination indicates that the ring lies in a chair form with tetramine equatorial positions. The configurations of the four chiral carbon centers are 3S, 5S, 10R and 12R. The methyl groups in 3S and 10R are disposed on opposite sides of the macrocyclic plane, and have an axial orientation. In addition, the methyl groups in 5S and 12R are also disposed on opposite sides of the macrocyclic plane, and have an equatorial orientation. (2) Crystal structure of 3,10-C-meso-5,12-C-rac-Me8[14]aneN4 (LC) The compound has a butterfly structure. The configurations of the four chiral carbon centers are 3S, 5S, 10R and 12S. The methyl groups in 3S and 10R are disposed on opposite sides of the macrocyclic plane, and have an axial orientation. On the other side, the methyl groups in 5S and 12S are disposed on the same sides of the macrocyclic plane, and have an equatorial orientation. (3) Crystal structure of [CuLB(H2O)2](ClO4)2 The molecule is located at an inversion. The compound is a six-coordinated octahedral complex with four N atoms of the macrocyclic ligand in the equatorial positions and two axial water O atoms in the trans axial positions; it belongs to the “4 + 2” type with four stronger Ni-N and two weaker Ni-O. The ligand is in its most stable, planar configuration with both the six-membered rings in chair forms and both the five-membered rings in gauche forms. The configurations of the four chiral nitrogen centers are 1R, 4S, 8S and 11R. The methyl groups in 3S and 10R are disposed on opposite sides of the macrocyclic plane, and have an axial orientation. The methyl groups in 5S and 12S are also disposed on opposite sides of the macrocyclic plane, and have an equatorial orientation. (4) Crystal structure of [CuLC(ClO4)2] The compound is a six-coordinated octahedral complex with four N atoms of the macrocyclic ligand in the equatorial positions and two axial perchlorate O atoms in the trans axial positions; it belongs to the “5 + 1” type with four stronger Ni-N bounds, one stronger Cu(1)-O(3) and one weaker Cu(1)-O(6). The ligand consists of both the six-membered rings in chair forms and both the five-membered rings in gauche forms. The configurations of the four chiral nitrogen centers are 1S, 4R, 8R and 11S. The methyl groups in 3S and 10R are disposed on opposite sides of the macrocyclic plane, and have an axial orientation. On the other hand, the methyl groups in 5S and 12S are disposed on the same sides of the macrocyclic plane, which the methyl group in 5S has an equatorial orientation and the methyl group in 12S has an axial orientation. (5) Crystal structure of [NiLB](ClO4)2 The compound is a four-coordinated square planar complex with both the six-membered rings in chair forms and both the five-membered rings in gauche forms. The configurations of the four chiral nitrogen centers are 1R, 4S, 8S and 11R. The methyl groups in 3S and 10R are disposed on opposite sides of the macrocyclic plane, and have an axial orientation. The methyl groups in 5S and 12S are also disposed on opposite sides of the macrocyclic plane, and have an equatorial orientation. (6) Crystal structure of [NiLC](ClO4)2 The compound is a four-coordinated distorted planar complex with two six-membered rings-one in a chair form and the other in a twist-boat form, and two five-membered rings-one of which is in a gauche form and the other in an eclipsed form. The configurations of the four chiral nitrogen centers are 1S, 4R, 8S and 11S. The methyl groups in 3S and 10R are disposed on opposite sides of the macrocyclic plane, in which the methyl group in 3S has an equatorial orientation and the methyl group in 5S has an axial orientation. On the other side, the methyl groups in 5S and 12S are disposed on the same sides of the macrocyclic plane, in which the methyl group in 5S has an axial orientation and the methyl group in 12S has an equatorial orientation. Ni(II) complexes with the tetraaza-macrocyclic ligands exist in aqueous solution as an equilibrium mixture of cis, trans, and planar species. The distribution ratios of the three species are related to temperature, ionic strength, pH value, and steric effect, etc. The blue-to-yellow reactions were carried out with a UV-vis spectrophotometer. The results of spectrophotometric studies indicate that the proportion of planar species increases by either an increase in temperature or by an increase of ionic strength. In addition, the proportion of planar species also increases by an increase of the number of methyl groups on the macrocyclic ligand. Furthermore, the axial methyl groups contribute to raise the standard equilibrium constant, ΔHo and ΔSo. This may be due to the steric effect and the distorted structure. In conclusion, [13]aneN4 provide the best fit cavity size for a square-planar Ni(II) complex. The order of the values of V (d-d) for square-planar Ni(I1) complexes is [13]aneN4 > [12]aneN4 > [14]aneN4 > [15]aneN4. In order to examine the effects of coordinated hydroxide ion and free hydroxide ion in configurational conversion of a tetramine macrocyclic ligand complex, the kinetics of the cis-to-planar interconversion of cis-[Ni(isocyclam)(H2O)2]2+ (isocyclam, 1,4,7,11- tetraazacyclotetradecane) has been studied spectrophotometrically in basic aqueous solution. The interconversion requires the inversion of one sec-NH center of the folded cis-complex to have the planar species. The proposed mechanism is a free-base catalyzed pathway because the metal-bound hydroxide ion cannot form a hydrogen-bonded chelate ring with the adjacent sec-NH。Furthermore, the kinetic data satisfactorily fits as the rate law, R = kOH[OH-][cis-[Ni(isocyclam)(H2O)2]2+], where kOH = 3.84 ´ 103 dm3 mol-1 s-1 at 25.0 ± 0.1 oC with I = 0.10 mol dm-3 (NaClO4). The large ΔH¹, 61.7 ± 3.2 kJ mol-1, and the large positive ΔS¹, 30.2 ± 10.8 J K-1 mol-1, strongly support a free-base-catalyzed mechanism for the reaction. On the other hand, the coordinated-base-catalyzed pathway results in a small ΔH¹ and a large negative ΔS¹ for cis-folded Ni(II) complexes of [13]aneN4, cyclam, C-meso-5,12-Me2cyclam, and C-rac-5,12-Me2cyclam. In higher base media, the kinetic studies were carried out by using a stopped-flow spectrophotometer and the resulting kinetic data provide different rate constants which are functions of ionic strength. This phenomenon gives good evidence for a free-base-catalyzed mechanism.