Silicon-containing macrocycles

The second problem concerns isomers of these various systems. As illustrated, 2d might be presumed to be planar. Unlike nitrogen, the inversion at phosphorus is very slow and there are, in fact, five possible isomers of it (three meso and two dl pairs). The interconversion of these isomers is reported in a subsequent paper by Davis, Hudson and Kyba along with x-ray crystallographic data on the structure of the so-called isomer B . 

Kyba and his coworkers have made numerous phosphorus-containing macrocycles and many of these are recorded in the tables at the end of this chapter. In addition, this group has prepared and reported quite a number of arsinocycles. The observations concerning phosphorus macrocycles apply in general to the arsinocycles as well, but the inversion barrier is even higher for the latter than the former.  

Quite recently, Ciampolini and coworkers have reported the synthesis of two isomeric mked oxygen-phosphorus macrocycles and the crystal structures of their cobalt complexes. Synthesis of macrocycle 27 was accomplished by condensation of 1,2-bis-(phenylphosphino)ethane dianion with 2,2 -dichlorodiethyl ether in THE. The two isomers of 27 were isolated in 1.5% and 2% yield. The synthesis is formulated in Eq. (6.17), below. 

Examples of silicon-containing macrocycles are rare and are perhaps incidental to the report of crown-type compounds. Obviously, silicon is more like carbon than a heteroatom in its ability to complex a cation. Nevertheless, there is a recent report of a crown compound which contains silicon as part of the macroring. Liptuga, Irodionova 

Bradshaw and Hui, in their review of sulfur-containing macrocycles, have included the analog of compound 7 (this chapter) in which each carbon bridge is replaced by a dimethylsilyl bridge. Nevertheless, silicon-containing crown relatives remain rare. 

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Silicon-containing macrocycles have been prepared by a high-dilution condensation of a,w-difunctionaIized silicon derivatives with A -methyldiethan-... 

Bauer 1, Habicher WD (1997) Synthesis of new phosphorus-containing macrocycles. Phosphorus Sulfur Silicon Relat Elem 130 89-105... 

Similar condensation of phenyltriethoxysilane with a spirocatechol yielded the first macrocyclic tetrasiliconate, a tetraanion containing four pentavalent silicons (equation 24a)58b. NMR evidence showed that only one meso-stereomer (C2h symmetry) was formed in solution out of the four possible diastereomers. The 29Si chemical shifts of the two unique silicons in DMSO-dg solution were —86.3 and —86.9 ppm, respectively, consistent with a pentacoordinate silicate anion. 

D. AZA-CROWN MACROCYCLES CONTAINING ARSENIC AND SILICON ATOMS IN THE MACRORING... 

Tables listing the known aza-crown macrocycles containing sulfur, phosphorus, arsenic, and silicon atoms in the macroring are presented hereafter. Insofar as possible, tables are ordered by the number of heteroatoms and complexity of the substituents.

The synthesis of 2-(trialkylsilyl) thiophenes from 2-thienyllithium and the corresponding chloro-silanes is extremely facile and useful. Disilanes have also been used in this reaction, leading to macrocycles containing silicon (Scheme 124) <88T28i>. 2,5-Disilylthiophenes have been prepared similarly. Treatment of 2-thienyllithium with 0.5 equiv. of dichlorodimethylsilane yields (571) in 74% yield <92H(34)1085>. This could be converted to the macrocycles (572) and (573) by lithiation followed by treatment with dichlorodimethylsilane (Equation (53)). 

A novel extension of the metal-induced coupling of diynes involves the preparation of the red, moisture-sensitive zirconocene-containing polymer 5.39 (Eq. 5.18) with Mw=37,000 (PDI = 2.1) by GPC (relative to polystyrene) [101], Related organo-silicon polymers and macrocycles derived from the zirconocene coupling of MeC = CSiMe2C6H4SiMe2C = CMe have also been reported [102, 103],... 

In search for systems which could meet these requirements we investigate the potential of silicon-contaiiiing spacers for the syntheses of new tin-containing multidentate Lewis acidic macrocycles and report here preliminary results of our studies. 

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