Macrocycle saddle-shaped

Recrystallization of 76 (R=H) from CH2CI2 provided crystals adequate for X-ray structural determination. The molecule was found to be saddle shaped with a phenyl ring at each vertex and nadir. The alkynyl bonds were found to be essentially linear and to possess a mean length of 1.194 A, typical for the length of triple bonds in free butadiyne. Although 76 is a dehydrobenzoannulene possessing a 4n TT-electron circuit, the nonplanarity of the macrocycle alleviated much of the strain associated with a flat structure and thus precluded the possibility of anti-aromatic ring currents. 

The examples cited above represent part of an increasing body of structural information on chlorophylls, chlorins, bacteriochlorins and isobacteriochlorins (10-14 and references therein) that points to the remarkable flexibility of these molecules This ability of the macrocycle to adjust is not limited to hydroporphyrins but is also observed in porphyrins 5,10,15,20-tetra-n-propylporphinato lead (II) assumes a "roof" shape by folding along an axis defined by two opposite methine carbons with the two planes of the "roof" inclined at 22 to one another (15) In contrast, triclinic 5,10,15, 20-tetraphenylporphinato cobalt (II) is distinctly saddle shaped with the 3 carbons of adjacent pyrrole rings lying 40 66 and -0 66A above and below the plane of the four nitrogens (16) ... 

The porphyrinic complexes are all essentially planar. However, the simple porphyrin and tbp macrocycles are somewhat flexible, and can adopt a ruffled, or saddle-shaped distortion through twisting at the methine carbon atoms. These deformations cause almost negligible changes in electronic structure, but the conformational mobility offers an added element of subunit variability. 

Sessler and coworkers prepared two similar uranyl complexes 6.48 and 6.49. A single crystal X-ray diffraction study of the former revealed a saddle-shaped penta-phyrin macrocycle with the uranyl cation centrally coordinated in a nearly pentagonal bipyramidal fashion (Figure 6.4.3). Distortion from planarity arises, presumably. 

The lacunar cyclidene ligands are the first family of totally synthetic ligands to form both iron(II) and cobalt(II) Oj carriers. The molecular structure of the lacunar cyclidene complexes is most simply represented by the flat projection (la), while the stereochemistry is shown in Ib. Cyclidene refers to the parent macrocycle encircling the metal ion and the lacuna is the permanent void created by bridging the cleft arising from the saddle shape of the cyclidene macrocycle. 

Cu-diimine macrocycle compounds (31) are formed by Jaeger template condensations of diamines with acyl-substituted /3-keto imines (30) (Scheme 9). The acyl substituents on the macrocycles are labile and undergo a variety of reactions. Reaction with trifluoromethyl sulfonate produces reactive methoxy ethylidene diimine compounds (32), which react with amines to form saddle-shaped cyclidenes. With bulky substituents these compounds have a hydrophobic void above the metal ion which can accommodate a guest molecule, an effect enhanced when the... 

All of the mercuracarborand halide complexes react with silver acetate to form the silver halide and liberate the free macrocycle. X-ray crystallography on the THF complex of the host tetramercuracarborand [3d] and on an octa-B-ethyl derivative (prepared to facilitate solubility in hydrocarbon solvents) has revealed that both species have saddle-shaped 54 symmetry with the centers of the icosahedra well outside the plane of the four mercury atoms. [3a, d] The square planar conformation that is found in the chloride com-... 

High spin Mn " products of the dianionic N4 macrocycle (1%) of type [MnX(196)] where X is Cl, Br, SCN and Nj have been prepared. The chloro and bromo derivatives crystallize with a molecule of acetonitrile while the thiocyanate and azide derivatives were obtained unsolvated. In the former compounds, the acetonitrile may be weakly coordinated to the manganese ion. An X-ray structure determination of jMnNCS(196)] indicates that it has a square pyramidal coordination geometry with the NCS group N-bonded and coordinated in the axial position. As in other structures of this ring system, the macrocycle has a pronounced saddle shape. The Mn " ion is displaced 0.356 A from the N4-donor plane. " The overall structure is similar to that of the Mn" species, [Mn(196)NEt3], discussed previously. ... 

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