Reactions of trimethylstannide and trimethylsiliconide anions with aromatic and heteroaromatic substrates

A parallel study was carried out on the reactions of Me 3 Sn − and Me 3 Si − ions towards aromatic and heteroaromatic substrates in hexamethylphosphoramide (HMPA) as solvent. It was found that Me 3 Si − ions are more reactive and therefore less selective than Me 3 Sn − ions. In HMPA, PhI and PhBr react with Me 3 Sn − ions through an HME pathway. PhCl also reacts by an HME reaction, but under photostimulation the S RN 1 mechanism competes with the HME process. With PhF as substrate, Me 3 Sn − ions afford (4‐fluorophenyl)trimethylstannane, presumably through a hypervalent tin species. Under irradiation, the S RN 1 mechanism operates concurrently with the formation of the hypervalent tin species. Me 3 Si − ions, on the other hand, react with PhX (X = Cl, Br, I) to yield the ipso substitution product, presumably through the intermediacy of a hypervalent silicon species. PhF affords, upon reaction with Me 3 Si − ions, o ‐ and p ‐fluorotrimethylsilylbenzenes together with the ipso substitution product PhSiMe 3 . A novel type of nucleophilic substitution mechanism takes place with Me 3 Si − ions upon reaction with aromatic and heteroaromatic substrates without classical leaving groups in HMPA.