Macrocyclic squares

Stang and coworkers found that the interaction of bis[4-(4 -pyridyl)phenyl]-A3-iodane 146 with cis-(Et3P)2Pd(OTi)2 in acetone at room temperature results in hybrid A3-iodane-Pd tetranuclear macrocyclic square 147 via self-assembly [Eq. (118)] [227]. Its X-ray structure shows a planar rhomboid-like geometry rather than a perfect square. 

A new type of iodonium salts constitute the conformationally rigid, tetranu-clear macrocyclic ring systems dubbed molecular boxes. The relatively simpler tetraaryltetraiodonium salts were obtained from 4,4 -bis(diacetoxyiodo)bi-phenyl and 4,4 -bis(trimethylsilyl)biphenyl [119]. The iodonium salt derived from 4-(4 -lithiophenyl)pyridine was made using the method of /J-(dichloroio-do)chloroethylene and it was used for the construction of hybrid iodonium-platinum (or palladium) cationic tetranuclear macrocyclic squares including some in which the ligand of the metal was a chiral biphosphine [120,121]. 

Stang et al. [94JA4981, 9403776, 95JA1667, 95JA6273] described the self assembly of a series of unique cationic, tetranuclear, Pd(II)- and Pt(II)-based macrocyclic squares (e.g., 25), utilizing different bidentates as the sides of these structures. The similar self-assembly complexation of dipyridyl porphyrins by cis- and tran.v-substituted Pd(II) or Pt(II) ions possessing square planar coordination afforded multiporphyrin arrays with a square... 

The cycloaddition reaction proceeds under more rigid conditions and takes more time than a direct template condensation on the iron(II) ion. This can be explained by the fact that the overall mechanism of clathrochelate synthesis involves an intermediate tris-complex formation step. It is evident that macrocyclic square-planar iron(II) bis-dioximates are relatively kinetically stable, and the... 

Coronenes, Crown ethers, Cryptands, Macrocycles, Squares, Rectangles... 

In recent years numerous macrocyclic square planar complexes have been prepared with various donor atoms and one or more transition metals. None of these complexes have been shown to exhibit extended metal-metal bonding. The physical properties of square planar phthalocyanine complexes have been the most extensively studied of these materials. The macrocylic planar dianionic phthalocyanine ligand forms numerous planar complexes with almost every transition metal (31,318). Crystallographically, the complexes stack in... 

With their preference for square planar coordination, palladium(II) and platinum(II) are well suited to binding to porphyrins and related N4 donor macrocycles. Therefore, Pd(octaethylporphyrin) is readily synthesized starting from the labile PhCN complex (like the platinum analogue) [92]... 

It has square planar coordination (Pd-N 2.010-2.017 A) similar to the value of 2.009 A in the tetraphenylporphyrin analogue, prepared by a similar route. As with nickel, macrocycle complexes can be made by in situ template... 

With a tridentate ligand Au(terpy)Cl3.H20 has, in fact, AuCl(terpy)2"1" with weakly coordinated chloride and water while Au(terpy)Br(CN)2 has square pyramidal gold(III) the terpyridyl ligand is bidentate, occupying the axial and one basal position [124]. Macrocyclic complexes include the porphyrin complex Au(TPP)Cl (section 4.12.5) cyclam-type macrocyclic ligands have a very high affinity for gold(III) [125],... 

The template-directed preparation of cycloi is(paraquat-4,4 -biphenylene (a molecular square ) has been achieved the use of a macrocyclic hydroquinone-based polyether template incorporating an ester moiety in one polyether chain afforded a 1 1 mixture of two topologically stereoisomeric [3]catenanes <96CEJ877>. 

To mimic the square-pyramidal coordination of iron bleomycin, a series of iron (Il)complexes with pyridine-containing macrocycles 4 was synthesized and used for the epoxidation of alkenes with H2O2 (Scheme 4) [35]. These macrocycles bear an aminopropyl pendant arm and in presence of poorly coordinating acids like triflic acid a reversible dissociation of the arm is possible and the catalytic active species is formed. These complexes perform well in alkene epoxidations (66-89% yield with 90-98% selectivity in 5 min at room temperature). Furthermore, recyclable terpyridines 5 lead to highly active Fe -complexes, which show good to excellent results (up to 96% yield) for the epoxidation with oxone at room temperature (Scheme 4) [36]. 

Macrocyclic receptors made up of two, four or six zinc porphyrins covalently connected have been used as hosts for di- and tetrapyridyl porphyrins, and the association constants are in the range 105-106 M-1, reflecting the cooperative multipoint interactions (84-86). These host-guest complexes have well-defined structures, like Lindsey s wheel and spoke architecture (70, Fig. 27a), and have been used to study energy and electron transfer between the chromophores. A similar host-guest complex (71, Fig. 27b) was reported by Slone and Hupp (87), but in this case the host was itself a supramolecular structure. Four 5,15-dipyridyl zinc porphyrins coordinated to four rhenium complexes form the walls of a macrocyclic molecular square. This host binds meso-tetrapyridyl and 5,15-dipyridyl porphyrins with association constants of 4 x 107 M-1 and 3 x 106 M-1 respectively. 

The fe-Ir1 complex (344) of the selena sapphyrin ligand has been synthesized and characterized by X-ray diffraction studies.551 The pairs of bound N atoms in (344) are bent towards the Ir1 centers, and the respective pyrrole rings are twisted from the macrocyclic plane. The coordination geometry around the Ir is close to square-planar, and the Ir Ir distance is 4.233 A. The Se center is not involved in bonding to the Ir centers. 

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