Non-transition metal catalytic systems able to activate hydrogen and other small molecules are focused in the literature review. Special attention is given to synthesis and reactivity of novel metal free catalytic systems based on bulky Lewis acids and bulky Lewis bases known as frustrated Lewis pairs (FLPs). N/B, C/B and P/B pairs previously identified as active catalyst are described together with the available mechanistic studies developed to clarify experimental findings obtained hitherto.
In the experimental section, synthesis of the Lewis acid mono(perfluorophenyl)borane was studied thorough several routes obtaining the borane in almost quantitative yield as a series of dimers including the anti- and syn-isomer with a low percentage of bis(perfluorophenyl)borane. Hydrogen activation was not possible because dimerization avoided further reactivity of the boron center in the presence of bulky amines.
A new synthetic route to obtain C6F5BCl2 in 58% yield was proposed and Lewis acid reactivity of the dichloro(perfluorophenyl)borane was studied with bulky amines exhibiting frustration although no hydrogen activation was achieved when purging hydrogen into the FLP solution. Instead, disproportionation of chloroborane species was promoted affording mixtures of (perfluorophenyl)boranes derivatives instead of an ammonium borate salt resulting from hydrogen activation.
The new adduct (t-Bu)2PSHBH(C6F5)2 was synthesized as a pure compound in more than 95% yield. Further studies are necessary to evaluate hydrogen release and hydrogenation activity of the compound.
