Reactivity of NHCs and related molecules with main group element hydrides and organyls

We recently extended our interest to investigations concerning the reactivity of NHCs with main group element hydride and alkyl/aryl compounds, respectively. These efforts are closely related to our activities in the area of NHC ring expansion (see below). In principle, the NHC can act here either as a Brönstedt or Lewis base leading to imidazolium salts or main group element NHC adducts, which may further react e.g. to give ring expansion products or other species.

For example, we have reported recently (H. Schneider, D. Schmidt, U. Radius, Chem. Eur. J. 2015, 21, 2793-2797) that the reaction of iPr₂Im (iPr₂Im = 1,3-di-iso-propyl-imidazolin-2-ylidene) with diphenyldichlorosilane Ph₂SiCl₂ leads to the adduct (iPr₂Im)SiCl₂Ph₂. Prolonged heating of isolated 1 in THF affords the backbone tethered di(imidazolium) salt [(^aHiPr₂Im)₂SiPh₂]²⁺2Cl^- (“^a” denotes “abnormal” coordination of the NHC). We have also demonstrate in a recent contribution that NHCs can be used in the dehydrogenative coupling of main group element hydrides. The dehydrogenative coupling of primary and secondary phosphines RPH₂ and P₂PH with iPr₂Im leads to R₂P–PR₂ or to NHC phosphinidene adducts iPr₂Im=PAr and cyclic oligophosphines P₄Ar₄, P₅Ar₅ and P₆Ar₆, respectively. The NHC acts in these reactions as phosphine activator and hydrogen acceptor.