Synthesis of Multinuclear Rh(I) Complexes Bearing Triazolylidenes and Their Application in C–C and C–Si Bond Forming Reactions

Multidentate carbene ligands are
valuable frameworks for the preparation
of carbene complexes displaying higher nuclearity. In the present
work, we report the synthesis of a series of mono- to tetra-[Rh­(COD)­I]
complexes (3a–d) supported by mesoionic
triazol-5-ylidenes. The general synthetic procedure involves the one
step reaction of the appropriate triazolium (2a–d) salt in the presence of KHMDS and stoiquiometric amounts
of the rhodium­(I) precursor. Treatment of complexes 3a–d with an excess of carbon monoxide allows for
the quantitative preparation of complexes 4a–d featuring a [Rh­(CO)2I] fragment used for the
detemination of the donor properties of the new triazolylidene ligands.
All complexes have been fully characterized by means of 1H and 13C NMR spectroscopy, melting point, elemental analysis,
and in the case of complex 3a, by X-ray crystallography.
Comparison of the catalytic activity of the new rhodium complexes
in C–C and C–Si bond forming processes demonstrate the
enhanced performance of the tetranuclear species suggesting the possibility
of strong cooperative effects in these multinuclear complexes.