Trimeric structures compounds

A structurally related tetrameric macroheterocycle is compound 13 that is prepared in a one-pot synthesis (yield 64%) from salicylaldehyde and (3-aminophenyl)boronic acid in methanol (Fig. 4). Due to its insolubility it has been characterized only by mass spectrometry. If a substitutent is introduced at the imine function (R = Me, Ph), trimeric structures (14 and 15) are... 

Di-f-butyltin oxide has a trimeric structure (102). Arylboronic acids can condense into trimeric structures and can displace tin sectors from 102, as shown in reaction 35. The structure of these compounds was elucidated by X-ray crystallography289. 

That Robinson s and Ewins compounds did in fact have the trimer structures 1 and 2, respectively, was only established 50 years later by the works of Lindsey [3], Erdtman et al. [4], and Goldup et al. [5], The name cyclotriveratrylene (CTV) was given by Lindsey to 1, which was shown by NMR to adopt the locked crown conformation shown on the stereoformula and later evidenced by X-ray crystallography (Fig. 1) [6, 7], More recently [8], the inversion barrier of the crown in 1 was found to be ca. 26.5 kcal mol 1 from the racemization rate of the isotopically chiral C3-cyclotriveratrylene-d9 (3) relatively uniform values (AG 26.5 to 27.2 kcal/mol) were found [9] for a variety of chiral cyclotriveratrylenes, including the parent compound 4, C3-cyclotribenzylene-d3. Thus, in these compounds, the half-life of a crown conformer in solution is around one month at 20 °C, a few minutes at 100 °C and less than 0.1 second at 200 °C. 

The uranium compound has a cyclic trimeric structure. Each uranium is individually in pseudotetrahedral coordination. It undergoes various reactions (Figure 13.12). 

In contrast to the dimeric triaUcylaluminum compounds, many diaUcylaluminum hydrides prefer trimeric structures with bridging hydrides as shown for BU2AIH (3). Uhl and coworkers have prepared and structurally characterized the novel tetrameric sesquihydride [ Bu3Al2H3]2 (4), which also exhibits bridging hydrides with large Al-H-Al angles of 149(2) and 155(2)°. ... 

The structure of the alkoxyboron difluorides has recently aroused some interest, and the historical consideration of the structure of these compounds has been outlined. Although the chemical shifts of these compounds are comparatively high (+01 to -f0 8) this does not imply quadricovalency (see above discussion) > however, the formation of the pyridine co-ordination complexes of the alkoxyboron difluorides (11) did not give appreciably higher B chemical shifts, and it was concluded that the boron atom in alkoxyboron difluorides was already tetracovalent. Molecular-weight determination confirmed the trimeric structure similar to the boroxole ring system. 

Palladium(II) acetate is usually prepared by the reaction of Pd sponge in hot glacial acetic acid with nitric acid as oxidant. A slight excess of Pd sponge must be used to make sure that all the HNO3 is consumed. Several other palladium(II) carboxylates can be obtained similarly. The crystal-structure determination of the acetate reveals a trimeric structure with bridging acetates in the solid state (1). Thus, the compound is better formulated as [Pd(/u,-02CMe)2]3. 

The chemistry of small molecule phosphazene ctm be traced back to tbe discovery that phosphorous pentachloride and ammonium chloride react to yield a mixture of compounds of which the main product is a volatile white solid, knowm to have the cyclic trimer structure, shown in Figure 3 (Ross, 1832 Liebich, 1834 Stokes, 1897). 

The hydrolytic activity of PET hydrolases and the resulting increase in surface hydrophilicity of PET by the addition of non-ionic surfactants such as Triton X-100 have been evaluated. The observed effects appeared to depend on the type of PET hydrolase used. Treatment of PET fabrics with the lipase from T. insolens in combination with Triton X-100 resulted in a strong increase in the hydrophilicity of the PET material [62]. Likewise, hydrolysis of the PET trimer model compound with the lipase from T. lanuginosus was strongly increased in the presence of Triton X-100, which can be explained by the interfacial activation of lipases involved in the hydrolysis of PET substrates [27]. However, Triton X-100 did not increase the moisture regain of PET fabrics treated with a lipase from C. antarctica [60]. The hydrolytic activity of the PET hydrolases from T. fusca and F. solani were also not improved in the presence of Triton X-100 as can be expected from the lack of a lid structure and interfacial activation in cutinases [19, 27]. A considerable increase in the hydrolysis of PET fabrics and film by the... 

The compound [(Me5C5)2Sm(CNQHn)(p-CN)]3 has a trimeric structure in which three (Me5C5)2Sm units are connected by three CN-bridges and each Sm atom is also bonded to the terminal CNC Hu group. The X-ray data do not differ between C and N atoms in cyanide bridges [52]. 

Fig. 5 Dimeric and trimeric structures for compounds of the type [Me2Al(p-OR)]n...

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