Pyridylamido Zirconium and Hafnium Alkyl Complexes as Catalysts for the Tandem Carbon Dioxide Hydrosilylation to Methane

The control of single-site catalysts performance through the design and synthesis of versatile organic ligands with tunable donor atom sets is a challenging goal for both organometallic and homogeneous catalysis communities. Following our interest in the chemistry and catalysis of highly electrophilic metal ions combined with amido-pyridinate based ligands,1 we have recently investigated the structure and organometallic reactivity of a series of ZrIV/HfIV alkyl/amido complexes stabilized by a tridentate N-ligand containing a "rolling" benzoimidazole fragment. The ability of the latter to take part to the metal coordination sphere via an amidic or a pyridinic N-donor tunes the electronic properties of the binding pocket and provides different coordination environments: from a tridentate monoanionic k3{N,N,N-} to a tridentate dianionic k3{N-,N,N-} donor atom set. The metal precursor choice [MIV(Bn)4 vs. MIV(NMe2)4] is found to influence the final complex coordination sphere unveiling the occurrence of unexpected organometallic side-rearrangements. Selected alkyl species from this series have been successfully scrutinized for the tandem CO2 hydrosilylation to CH4 in combination with the strong Lewis acid B(C6F5)3 (as silane and complex activator) and a variety of hydrosilanes (see Figure). Organometallic reactivity and catalytic outcomes of the synthesized complexes will be presented in details.