The literature part goes over the discovery of frustrated Lewis pairs, and their use in catalysis to effect hydrogenation. It spans the road from simple hydrogen activation to asymmetric hydrogenation of substrates. The topic is limited to substrates with polar double bonds and amino- and phosphinoboranes as catalysts.
The research comes in three parts. The first part was catalysis testing a newly found aminoborane in hydrogenation reactions in mild conditions. This entailed relatively normal laboratory glassware: Schlenk tubes and the Schlenk line to provide the inert gas atmosphere and of course the hydrogen gas itself. The second and third part are concerned with catalyst synthesis. The second was attempting to create Lewis acids in the image of the catalyst in the first part, to gain more insight of the effects of the structure of the acid. The third similarly was concerned with creating a new variant of an already existing catalyst to see whether minor tweaking of its structure might improve its performance. For the second and third parts however, the synthesis was quite difficult, and catalysis was never reached.
Based on literature it was found that adduct formation did not necessarily exclude hydrogen activation, but that an equilibrium state was necessary for them to co-exist. However, sterically demanding environment was no longer a requirement for both the acid and base. For the reversible reaction to be feasible, the acid and base mustn't have too much affinity to their half of the hydrogen molecule. It seems that the acid has more impact on the reversibility of hydrogen activation, and it may be possible to modify an acid to make an irreversible activation reaction reversible. For enantioselective catalysis, the catalyst itself must introduce the element of chirality to the system, so that it may favour one orientation of the substrate over the other. Whether chiral or not, it seems clear that a hindered catalyst will prefer unhindered substrates and vice versa. This allows us to choose an appropriate catalyst for the substrate we have in mind. To that end, it is a good thing to have a spectrum of catalysts: specific tools for specific jobs.
In designing new chiral catalysts, it seems one needs to consider how to implement the element of chirality to the structure, the electronic and steric conditions, and the acidity and basicity of the acid and base groups. Especially worth considering are the 4- and 6-membered rings that form in the catalyst before and after hydrogen activation. 6-membered rings in the salt are especially worth avoiding.
The catalysis testing yielded preliminary results and guided the path to finding the most optimal conditions for each substrate tested. One of the catalysis syntheses suffered from straightforward difficulties in synthesis and purification, and larger, more complicated Lewis acids of similar structure have already been synthesized. Thus it doesn't seem likely that this particular branch of study is worth the effort, certainly not commercially. The other catalysis synthesis had the most difficulty in separating the diastereomers, which was time consuming. Therefore that branch doesn't seem very practical either.
