Cyclic tetramerization

Thereby, the presence of tertiary monophosphines is critical, because both polymeric (26) and cyclic tetrameric (24 and 25) complexes can be obtained depending on the phosphine added to the reaction mixture. Furthermore, with some of the phosphines rapid decomposition and deposition of metallic silver occurs. In the macrocyclic molecules 24 and 25 a pair of silver atoms is bridged by two bis(l-imidazolyl)borate moieties, with a transannular Ag Ag distance of 8.61 A for 24 and 8.89 A for 25. The conformations of 24 and 25 are... 

E. and Randaccio, L. (1992) Gold(III) glycyl-L-histidine dipeptide complexes. Preparation and x-ray structures of monomeric and cyclic tetrameric species. Inorganic Chemistry, 31, 1983 (b) Carotti, S., Marcon, G., Marussich, M., Mazzei, T., Messori, L., Mini, E. and Orioli, P. (2000) Cytotoxicity and DNA binding properties... 

By switching to a cyclic tetrameric hydridomethylsiloxane a processable, partially crosslinked liquid precursor could be obtained with Mn = 1.2-1.5 KDa (equation 20). 

Lehn reported the synthesis and solid-state architecture of chiral 2,5-diazabicyclo[2.2.2]octane-3,6-dione. The racemic material adopted an infinite chain of alternating (+) and (-) units, whereas the single enantiomer formed a cyclic tetrameric structure (Fig. 11.14) [49]. 

Naphthol may form cyclic tetrameric condensation products with formaldehyde among which 101 has a C4 axis.194 However, since the OH groups are in exo positions in this case (in contrast to the calix[4]arene 97g derived from 2-naphthol) it seems difficult to fix a nonplanar conformation in these cases.195 A possibility would be the connection of two opposite oxygens by a (crown) ether bridge which would lead to a C2-symmetrical derivative. 

The reaction of lithiated derivatives of l,2-C2BioHi2 with mercury(II) halides is a route to organomercury complexes with Hg-Ccarbabotane bonds. " Au interesting example is shown in Scheme 3 l,2-Li2-l,2-C2BioHio reacts with HgL to give Li2[Hg4(C2BioHio)l2]. When Lil is removed, a cyclic tetrameric complex, which is described as a macrocyclic Lewis acid, is produced. 

There are several ways to synthesize the homoleptic bis(phthalocyaninato) rare earth complexes RE(III)(Pc02, Figure 4.35. The simplest way is to heat a mixture of a metal salt and phthalonitrile in a ratio of approximately 1 8 to 280-290 °C followed by chromatographic separation of the product [57]. Alternatively, this cyclic tetramerization method towards RE(III)(Pc02 could be conducted with an organic base such as l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a promoter [58]. In addition, a ligand condensation method also plays an important role in the synthesis of homoleptic bis(phthalocyaninato) rare earth complexes. This procedure is based on the reaction of H2PC or Li2(Pc ) with rare earth salts in a solvent with a... 

H2-Py4P, 49) is added to a solution of the cyclic tetrameric Zn4-48, it leads to the formation of a strong 1 1-complex 50. 

Very recently, the first cyclic tetrameric, pentameric, and hexameric 3-APs, with Cio alkyl chains, have been isolated in a mixture from the sponge of the genus Haliclona [28]. The structure of these compounds, cyclohaliclonamines A-E (69-73), is shown in Fig. (18). 

Ketones of the general structure 265 have complexing features rather similar to those of the esters 264. Stability constant measurements and extraction data indicate that the cyclic tetrameric ketones are better than their ester analogs for the extraction of Li and also for Rb and Cs". The ketone 265c has a broader range of extraction capability than its cyclic tetramer and hexamer counterparts but shows little selectivity among the cations. 

Amides of the general structure 266 were first prepared and studied by Ungaro and coworkers and subsequently in considerable detail by McKervey and coworkers and Beer and coworkers. The cyclic tetrameric amides... 

The stmcture of solid-state aluminum isopropoxide was determined at 25°C in 1979 by Turova et al. (23) confirming Bradley s assertion of a possible non-cyclic tetrameric form (24). Folting and coworkers studied crystalline aluminum isopropoxide by X-ray diffraction as well as proton and a1 NMR. They determined it to be a tetrameric material having the following formula, Al[(/trO Pr)2Al(0 Pr)2]3, which supports earlier stmctural proposals (24,25) and the spectroscopic data of other researchers (15,18). The tetrameric form of aluminum isopropoxide is depicted in Figure 2 where the octahedral, central Al... 

---