Pyrene-Based Mono- and Di-N-Heterocyclic Carbene Ligand Complexes of Ruthenium for the Preparation of Mixed Arylated/Alkylated Arylpyridines

By using two pyrene-based mono- and
di-N-heterocyclic carbene ligands,
two ruthenium complexes (one monometallic and the other dimetallic)
have been obtained and fully characterized. The molecular structure
of the dimetallic complex has been determined by means of X-ray diffraction
studies. The electrochemical studies reveal that the metal–metal
communication in the dimetallic complex is weak. The catalytic activity
of both complexes has been tested in the arylation of arylpyridines
with aryl halides and in the hydroarylation of alkenes, where they
showed similar activity. The sequential combination of these two catalytic
processes (hydroarylation of alkenes followed by arylation of the
resulting alkyl-substituted arylpyridine) allowed the preparation
of mixed arylated/alkylated arylpyridines. In this tandem process,
the dimetallic complex afforded activity higher than that of the monometallic
complex. The activity was compared to that shown by the [RuCl2(p-cymene)]2 complex. This reaction
constitutes an efficient method for reaching unsymmetrically substituted
arylpyridines.