Preparation of polynuclear NHC complexes by post-synthetic modification of half-sandwich rhodium and iridium complexes bearing C-azolato ligands

A series of bimetallic and trimetallic complexes has been prepared by N-alkylation of mononuclear half-sandwich rhodium and iridium di-NHC complexes featuring bidentate chelate ligands composed of a classical NHC and a C-azolato donor. The shape and the separation between metal centers in the obtained complexes are highly dependent on the alkylating agent used. While the polynuclear complexes were formed as diastereomeric mixtures according to NMR spectroscopy, X-ray diffraction analysis revealed their remarkable preference to crystallize as meso compounds. The reactivity of the bimetallic, olefin-bridged complexes in electrophilic addition reactions has been investigated.