Weak-donor conditions

WEAK-DONOR CONDITIONS STRONG-DONOR CONDITIONS... 

The hydrated chloride, bromide and iodide (Table 9) are soluble in ethanol, butanol and other organic solvents, but in many systems traces of water cause oxidation, hydrolysis or failure to complex with weak donor ligands. Water can be avoided by dissolving the metal in THF, ethanol or diethyl ether through which hydrogen chloride is bubbled.24,74 75 It is also possible to dissolve or suspend in organic solvents the anhydrous acetate or the halides CrX2 (Table 9), and dehydration of the hydrated halides with 2,3-dimethoxypropane in ethanol, followed by vacuum removal of the liquid, produces mixed alcoholates suitable for use in water-free conditions.76 Triethyl orthoformate may be used similarly. 

Under certain conditions, apparently when the Cr(CO)3 unit is spontaneously displaced from the product by a weak donor ligand (solvent), the simple addition product (1,3-cyclohexaidiene derivative 31) can be the major product (equation 20).71... 

In order for the composites to become conductive, the TCNQ salt, initially dissolved in DMF solution before casting, should subsequently recrystall ze as pure microcrystals. To realize this condition with NMP TCNQ7, two approaches are possible one is to reduce the association through choosing weak donor polymers as matrices, and another is to dope the system with TCNQ so that TCNQ salt association with the polymer should be reduced through a competitive reaction with TCNQ, thereby facilitating salt crystallization. 

A necessary but not sufficient condition for efficient extraction by a pure liquid appears to be the presence of an electron donor atom, c.g. a basic oxygen or nitrogen atom, d he possession of an appreciable dielectric constant favors extraction by a liquid even when only weak donor atoms are present. 

Our ultimate goal, the control of the reactivity of silylium ions is very ambitious, and we are still far away from a chemistry of cationic silicon in solution, in particular from a controlled chemistry. The benefits of our model system 1, however, are already obvious. The two silicon substituents confer to the cyclic cations 1 a high thermodynamic stability. An example is shown for the arenium ions 9 and the vinyl cations 11 and 12 and can be easily extended to every substituent X acting as a Tt-donor, such as alkenes, nitriles, allenes or azides. In addition the very weakly nucleophilic conditions applied in our reactions allow the generation of only weakly stabilized cations with very uncommon structural features, as for example the hydrogen bridged ion 16. 

Complexes formed by weak interactions of electron donors with electron-acceptor compounds are known as charge-transfer complexes. The necessary condition for the formation of a charge transfer complex is the presence of an occupied molecular orbital of sufficiently high energy in the electron-donor molecule, and the presence of a sufficiently low unoccupied orbital in the electron-acceptor molecule. Small unsaturated hydrocarbons are usually weak donors or weak acceptors. Polynuclear aromatic... 

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