Thermodynamic data arene complexes

Medium effects on adduct formation are best analysed by considering the solvation properties of the species involved. Thus, using transfer thermodynamic data for p-terr-butylcalix[4]arene (Table I), corresponding values for triethylamine from benzonitrile to nitrobenzene (A(G° = -1.11 kJ mol, Ajl = 1.67 kJ mol and AtS = 9.3 J mol ) combined with the complexation data in these solvents given in Table IV, the thermodynamic parameters for the transfer of the triethylamine-p-tert-butylcalix[4]arene adduct [R3N-calix[4]] between these two solvents are calculated by inserting the appropriate quantities in the following cycle, where P = G, H or S. 

Table 21 Some thermodynamic data on bis-n-arene complexes...

With few exceptions, transition metal complexes of terminal alkyl groups are more stable than those of isomeric secondary or tertiary alkyl groups. Consistent with this trend, the terminal alkylmetal hydride complexes of systems that undergo oxidative addition of C-H bonds are thermodynamically more stable than the branched alkylmetal hydride complexes. "- The oxidative addition of alkanes by the Cp Ir(PMe3) fragment is reversible, and this reversibility allowed for an evaluation of the thermodynamic stability of alkyl hydride complexes formed from a series of alkanes, as weU as from arenes. These data showed that the alkyl hydride complex formed from oxidative addition at the primary C-H bond leads to more stable products than those formed from... 

Cis-trans isomerism in octahedral complexes is shown in structures [5-7] and [5-8], Norbornadiene molybdenum tetacarbonyl can assume only the cis form, as seen in [5-9]. Arene 71-complexes also may exhibit cis-trans isomerism. X-ray diffraction data have shown that of the two structures [5-10] and [5-11], which could exist for ditoluenechromium(O), the thermodynamically more stable structure [5-11] exists under ordinary conditions. Dibi-phenylchromium(O) [5-12] and [5-13] may also exist in at least two forms. 

Synthetic developments in the area of Supramolecular Chemistry are currently leading to a massive production of new macrocycles. The driving force for this continuous growth is the search for selective hosts to target a particular neutral or ionic species. There is no doubt that the impact produced by the discovery of macrocyclic ligands such as the crown ethers [1] and the cryptands [2] resulted from their cation complexation and this prompted us to consider the thermodynamic characterisation of these systems (mainly cryptands) which has been extensively reported [3-5]. Calixarenes, an important class of macrocyclic compounds, are products of the base-catalysed condensation reaction of p-substituted phenols and formaldehyde [6, 7]. These compounds are characterised by their low solubilities in most solvents, although until recently [8], no quantitative data has been reported. Functionalisation of the lower or upper rim of parent calix[n]arenes has... 

---