Nitrogenated lewis bases methylation

As a conclusion to this section it should he mentioned that reactions between diborane and several other nitrogen Lewis bases besides those mentioned above have been investigated. These nitrogen donors include hydrazine and its methyl derivatives (130), hydroxylamine and its. V-metliyl derivatives (45), and O-methylhydroxylamine and its A-methyl derivatives (11). In general, borane adducts are formed (Table II) which are thermally unstable with respect, to release of hydrogen. 

As seen from Table IV, the feature most characteristic of the formation of a matrix silylene-Lewis base complex is the hypsochromic shift of the visible absorption band of the silylene on complexation. At this point it is worthwhile to mention that as early as 1982 it was reported28 that the absorption maxima of methyl-substituted silylenes in a nitrogen matrix are shifted to significantly higher energies than those of the same silylenes in an inert argon matrix. However, the cause of the shift difference was not addressed in this publication. 

A substantial portion of the early interest in MTO pertained to its use in alkene metathesis.12 Of more relevance to oxidation processes, much work has also involved examining Lewis base adducts of this electrophilic, (formally) 14-electron complex. Generally, nitrogen bases coordinate trans to the methyl group. Bidentate ligands such as bipyridyl lead to the fac-Me(N N)Re03 isomer of the octahedral complex. Table I summarizes some of the structural information from X-ray crystallographic and infrared studies. 

Although the starting methyl compound exists as a mixture of the geometrical isomers, the acetyl derivative occurs only with the acyl group cis to the nitrogen atom of the pyridine ligand. Kinetic studies have shown that the rate of CO insertion decreases as the Lewis base character of the tertiary phosphine increases. 

To improve upon the selectivity of the ketimine reduction process further, the hydrosilylation of a range of substrates derived from (/ )- -phenylethylamine were examined [37]. Optimization of the reaction conditions allowed obtaining complete diastereoselective reduction of a wide range of acetophenone-derived ketimines as well as a-imino esters, demonstrating the cooperative effect of catalyst and the (/ )-methyl benzyl residue at the imine nitrogen. In this context, we reported also a low cost protocol for a highly stereoselective reduction of ketimines bearing a very cheap and removable chiral auxiliary, promoted by an achiral inexpensive Lewis base, such as DMF [38]. 

Craig (2) has recently reported the results of studying the reactions of several nitrogen-fluorine compounds with Lewis acids. As expected he found that all the compounds he studied were extremely weak bases, difluoramine and its methyl derivative being among the strongest. Here we report some of our data on the reactions of the latter compounds with other strong acids. 

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