Toluene diamine complexes

Direct and selective conversion of esters into ketones, a fundamental reaction but difficult to achieve, has been accomplished by Ahn and co-workers [59] by use of organoaluminum-diamine complexes. The reaction of methyl benzoate with MesAl (3.1 equiv.) and A V -dimethylethylenediamine (DMEDA) (1.1 equiv.) in toluene under reflux followed by an aqueous work-up produced only acetophenone in almost quantitative yield (98 %). Notably, ketones and even aldehydes survive under the reaction conditions. A mechanistic investigation established that the conversion proceeds through transamidation and subsequent intramolecular nucleophilic attack mediated by organoaluminum complexes this provides an explanation of the need for 3 equiv. MesAl for the fast reaction (Sch. 35). 

The easiest access to most benzyllithium, -sodium, or -potassium derivatives consists of the deprotonation of the corresponding carbon acids. Hydrocarbons, such as toluene, exhibit a remarkably low kinetic acidity. Excess toluene (without further solvent) is converted into benzyllithium by the action of butyllithium in the presence of complexing diamines such as A. Af.Af.jV -tetramethylethylenediamine (TMEDA) or l,4-diazabicyclo[2.2.2]octane (DABCO) at elevated temperatures1 a procedure is published in reference 2. 

The synthesis of this salt started with the enantiomerically pure 1,2-diamine 106, that was converted into the corresponding thiourea derivative 107 (Scheme 12). Exposure of the thiourea 107 to oxalyl chloride in toluene at 60 °C cleanly afforded the desired imidazolinium chloride 108. These two salts were used to produce new palladium and nickel carbene complexes. The structure of both palladium carbene complexes 96a and 96b has been elucidated by X-ray diffraction <2005CEJ1833>. 

A study was carried out applying Li and C NMR spectroscopies, on the behavior of Li-enriched BuLi and PhLi (RLi) in toluene solution, in the presence of chelating diamines 141-143 and (—)sparteine (24), denoted by L. Dimeric complexes 2RLi-2L... 

In the application of membrane technology (cf. Section 3.2.3) for the separation of the Rh complexes and the re-immobilized ligands after the reaction, a further remarkable enlargement of the ligands was desirable. Unfortunately, the combination of diamines with TPPTS yields highly crosslinked polymeric materials, which cannot be handled. A reduction of the degree of crosslinking is possible by use of the disulfonated TPPDS (cf. Section 3.1.1.1). So, in a combination with TCD-diamine (tricyclodecane diamine) a salt was formed that was partly soluble in toluene and soluble in THF. The same was the case with the use of MA -dimethyl-TCD-diamine. These salts may be useful in water-free two-phase catalyst systems. 

The crystalline yellow 1 1 benzyllithium-TMEDA complex has a lower solubility in toluene than does the (benzyllithium )2-TMEDA complex which tends to form oils. Because of its higher solubility and to eliminate as much of the tertiary diamine as possible, the 2 1 complex was used for synthetic evaluations. It is probably the optimum ratio to use in this benzyllithium system. Solutions of up to 38 wt % benzyl-lithium in toluene or about 59 wt % of the (benzyllithium )2-TMEDA complex have been prepared. At ratios of 4 1 or more in toluene, a dark-red tar or oil also separated from the solution. With hexane as the solvent, yellow crystals of the 1 1 benzyllithium-TMEDA complex precipitated at a ratio of 2 1 or more, a dark-red oil separated instead. 

The deprotonation proceeds smoothly below -70°C within a few minutes using sec-butyUithium in ether, hexane, or toluene in the presence of the complex-ing diamine TMEDA. The Ai,N-diisopropylcarbamates of type 216 are stable with respect to configuration and to decomposition under these conditions, whereas benzoates 217 decompose more rapidly. 

Similarly complex 97 formed by the condensation of 2,2-diethyl-propane-1,3-diamine and 3,5-di-terf-butyl-salicylaldehyde and then with AlEtj in toluene and heptane at 100 C for 24 hrs (Scheme 6.21). This aluminum complex in the presence of isopropanol acts as initiator to produce PLA with narrow PDI (Table 6.14) [72]. 

The direct conversimi of esters into amides is a synthetically useful transformation. However, most of the methodologies developed till now usually require harsh reaction conditions, are poorly compatible with sensitive substrates, and present a low atom economy [136, and references cited therein]. Very recently, MUstein and co-workers demonstrated that esters can be selectively converted into amides generating molecular hydrogen as the only by-product (Scheme 31) [137]. The catalytic reactions were carried out with 2 equiv. of amine per ester in toluene or benzene at reflux in the presence of 0.1 mol% of the dearomatized PNN-pincer ruthenium complex [RuH(CO)(PNN)] (28) (see Scheme 21). Strikingly, both the acyl and the aUcoxo units of the starting ester are involved in the amide production. Hence, to avoid mixtures of products, the process was only applied to symmetrical esters. The catalytic protocol was effective for both primary and secondary cyclic amines. In addition, the coupling of piperazine and butylbutyrate provided compound 46, which results from the bis-acylation of the diamine (Scheme 31). 

A second approach adopted by O Brien and co-workers (1841, 1849) is the preparation of bis(dithiocarbamate) complexes generated from trimethylethy-lene and trimethylpropylene diamines. The former gives fairly insoluble products that were not pursued, but the latter are soluble in toluene and benzene and were successftdly used to deposit thin films of ZnS and CdS on glass, which gave better quality films than [Cd(S2CNEt2)2]. 

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