Zr Ti molecular and silica-supported imido complexes in stoichiometric and catalytic oxo/imido heterometathesis

Surface Organometallic Chemistry (SOMC) aims at selective preparation of unusual or highly reactive species on the surfaces of inorganic supports in order to reach a better understanding of classical heterogeneous catalysts and discover new reactivities and catalytic transformations. SOMC relies on the application of both surface science techniques and molecular organometallic chemistry; in particular it requires rational design of the molecular precursors to ensure their selective reactivity with the supports. In this report we apply the SOMC protocols to prepare well-defined silica-supported Zr imido complexes. We describe the synthesis of Zr imido pyrrolyl complexes Zr(&z.dbd;NR)(Me 2 Pyr) 2 (py) 2 (R = t Bu ( 1a ), Ar ( 1b ); Ar = 2,6-iPr 2 C 6 H 3 , Me 2 Pyr = 2,5-dimethylpyrrolyl, py = pyridine), investigate their grafting onto the surface of partially dehydroxylated silica and evaluate the obtained materials as oxo/imido heterometathesis catalysts in comparison with the previously reported highly active supported Ti systems. We also investigate the stoichiometric oxo/imido exchange reactivity of Zr imides using Ph 2 CO as a probe molecule, compare them with isostructural Ti analogs Ti(&z.dbd;NR)(Me 2 Pyr) 2 (py) 2 (R = t Bu ( 2a ), Ar ( 2b )), and discuss how these results correlate with the differences in their electronic structure and catalytic performance of silica-supported species. Zr imido chemistry: well-defined silica-supported Zr imido complexes via Surface Organometallic Chemistry, oxo/imido heterometathesis and comparison with Ti analogs.