In a context where environment-benign processes are more than ever advocated, the removal of metallic contaminants and their replacement by non-toxic catalysts in organic synthesis is becoming a major scientific and industrial issue that needs to be addressed. For instance, applications of polymers in fields like microelectronics or living systems should be free of any metal residues. There is also a strong trend in decreasing, and ultimately eliminating toxic organometallic catalyst residues in applications related to the paints and coatings market. Very soon, metal-free organocatalysis was envisioned as a promising approach in order to put the concepts of green chemistry into practice.
NHC Carbene are particularly interesting organocalysts for their remarkable nucleophilic and basic characters.
- Synthesis and storage of NHCs under air
In spite of the great potential of NHCs in organic and organometallic chemistry, their air and moisture sensitivity is one of the most important problems for the development of the NHC chemistry from a practical point of view. We previously reported that the silicone derivatives were found to be efficient protecting media for NHCs, which allow manipulation or storage of NHCs under air without any special precautions (Angew. Chem. Int. Ed, 2007, 46, 8786 - FR 2006/10639
Now, we have developed a new methodology to synthesize NHC without the use of strong bases, which was a major drawback for their use in industry. The deprotonation of imidazolium salts in alcoholic solutions (iPrOH, EtOH, MeOH) using alcoolate type base (MeONa, tBuOK) or even hydroxides (NaOH, KOH) affords the corresponding carbenes in nearly quantitative yields. These reactions can be performed under air and the alcoholic solution of carbenes are stable for months at room temperature. Simple removal of the alcohol afford the pure carbenes (WO2011 083146).
The alcoholic solution can be used as pure carbene source for synthesis of organometallic complexes, organocatalytic transformation (transesterification) or as catalytic system for silicones polycondensation.
Organocatalyst for silicones reticulatio
Pentacoordinated phosphorus derivatives are very simple to synthesis and to purify. Their Lewis acidity justifies their use as catalyst for RTV1 and RTV2 for silicon synthesis. Therefor we have developed original organophosphorus catalysts that show activities in RTV1 comparable to tin catalysts