Macrocycle chair conformation

Nin(Me6[14]aneN4)Cl2], whose molecular structure is illustrated in Figure 108. The macrocycle assumes a chair conformation.157... 

Abbeiante, G. Fairlie, D.P. Gahan, L.R. Hanson, G.R. Pierens, G.K. van den Brenk, A.L.(1996) Conformational cmitrol by thiazole and oxazoline rings in cycloctapeptides of marine origin. Novel macrocyclic chair and boat conformations. J. Am. Chem. Soc. 118, 10384-8. 

Macrocycle 177 in which the 2,6-pyridino and the 1,4-piperazino moieties were incorporated into the macrocyclic framework has been reported. The synthesis of 177 (10%) was accomplished by treatment of 2,6-dichloropyridine with the dianion of Ar,Ar -W. (2-hydroxyethyl)piperazine in refluxing xylene. Attempts to prepare the cobalt(II) complex of 177 resulted in diprotonation of the macrocycle. The X-ray crystal structure determination analysis has been performed for both 177 and 178. According to the crystal structure analysis of 178, the piperazine rings are in the chair conformation in the solid state and the molecule is fairly rigid due to the imposed steric constraints of the imidate moieties l39). 

Cyclodextrins are macrocycles with limited flexibility. In all the crystal structure analyses of cyclodextrins, the glucose units have the D-pyranose configuration with the normal 4Ct chair conformation [556, 558, 559]. This chair form is nearly rigid, as illustrated by only small variations (<7°) of the intrapyranose ring tor-... 

Structures such as CA6, CA7, and CAS have a doughnut shape and are able to host small molecules inside their cavity. Similar to amylose, the glucose units in the CAs are linked by a(l 4) bonds that adopt a Ci chair conformation. They may be considered as rigid building blocks giving fairly limited conformational freedom of the macrocycle in rotation of the C6-06 groups and limited rotational movements about the glucosidic link Cl(n)-04(n - 1)-C4... 

Macrocycles 3, 4, 5 and 6 are all colorless, crystalline solids that are stable in the air and light indeilnitely at room temperatiue. None has ever exhibited any shock sensitivity. X-ray crystal structures of 3, [9] 4, [27] and 5 [27] have all been determined, and the structural resemblance between these macrocycles and the corresponding cycloalkanes with the same number of vertices is striking the [5]pericyclyne, 3, adopts an envelope conformation, the [6]pericyclyne, 4, adopts a chair conformation and the [7]pericyclyne 5, adopts a tub conformation. Unfortunately, the [8]pericyclyne, 6, crystallizes as fine hairs that are unsuitable for X-ray diffraction analysis. 

Figure 7.1 shows the structure of CyDs consisting of 6-9 glucose units. Some average parameters describing the macrocyclic conformation of native CyDs are summarized in Table 7.1. The pyranose ring of each glucose unit in native CyDs is relatively rigid and assumes the Ci chair conformation. Some structural characteristics of CyDs are illustrated in Fig. 7.2. Primary hydroxyl groups have rotational...

Fig. 16 General structure of the extended macrocyclic complex [38] and X-ray structure of a complex displaying the chair conformation of the bridging ligand reprinted with permission from [39], Copyright (2002) American Chemical Society...

The structural arrangement of coordinated groups around molybdenum is close to octahedral, indicating that the [12]aneP3 ring fits well without significant distortion of the bond angles at molybdenum. The macrocycle is positioned so that two of the six-membered metallocycles have chair conformations and the third cycle adopts the boat conformation. 

Several analogs of 145 were prepared in which the sulfur atom is oxidized to S=0 (148) and to SO2 (149) . AU the sulhnyl compounds (148) have the macrocycle in a chair conformation, and hence there is no S—Si coordination . In the sulfonyl analogs, however, one of the oxygens is coordinated to silicon, as long as the phenyl-ortho positions are occupied by t-butyl groups . 

The corresponding X-ray crystal structures of these triptycene-derived calixarenes and analogues were also obtained. As shown in Fig. 18.2a, b, macrocycle la adopted a typical cone conformation with a highly symmetric structure, while trans-isomer 2a adopted a chair conformation with two opposite phenol rings in the same plane [11a, b]. Similar stmctural features were also found in the crystals of their derivatives 5 and 6 [11c]. In the case of 7a, b and e [1 Id, e] (Fig. 18.2c) and 8a [12] (Fig. 18.2d), the crystal structures showed that they adopted cone conformations with fixed cavities while 7g [lie] was in a 1,2-altemate conformation. 

The general procedure for the preparation of vanadium borates consists in heating a concentrated H2O solution of boric acid and vanadium oxide in an autoclave at 170 °C for several days [143]. Two different vanadium borate clusters 105 and 106 are obtained, one with two polyborate chains coordinated to a contorted vanadium oxide ring (105) and another one with a macrocyclic Bi8036(0H)6 ring (106). The latter ring is composed of six B306(0H) units and has a chair-like conformation (Fig. 27) [143]. 

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