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We report here the preparation and characterization of new well‐defined silica‐supported Ti imido complexes that present an L‐ligand variation in a structure of currently the most active oxo/imido heterometathesis catalyst (≡SiO)Ti(=NtBu)(Me2Pyr)(py)2 (1s), where py is replaced with stronger electron‐donating 4‐(N,N‐dimethylamino)pyridine (2s) or bidentate 2,2′‐bipyridine (3s). The materials were characterized with elemental and mass balance analyses and IR and solid‐state NMR that confirmed the selective formation of surface Ti species with terminal imido ligand. Evaluation of the catalytic oxo/imido heterometathesis activity of the obtained materials demonstrated that L‐ligands have a pronounced influence on the catalytic performance. In particular, the replacement of pyridine with stronger donating ligands resulted in a significant drop of activity. The catalytic results are discussed in view of the reaction mechanism and implications for further catalyst development. [ABSTRACT FROM AUTHOR]

Continuing our investigation of catalytic oxo/imido heterometathesis as novel water‐free method for C=N bond construction, we report here the application of classical transition metal oxides dispersed on silica (MOx/SiO2, M=V, Mo, W) as cheap, robust and readily available alternative to the catalysts prepared via Surface Organometallic Chemistry (SOMC). The oxide materials demonstrated activity in heterometathetical imidation of ketones, WO3/SiO2 being the most efficient. We also describe a new well‐defined supported W imido complex (≡SiO)W(=NMes)2(Me2Pyr) (Mes=2,4,6‐Me3C6H2, Me2Pyr=2,5‐dimethylpyrrolyl) and characterize it with SOMC protocols, which allowed us to identify the position of W on the oxo/imido heterometathesis activity scale (Mo

We report here the synthesis of 4‐coordinate Ti imido complexes Ti(=NtBu)(OArtBu)2(py) (2) and Ti(=NtBu)(OArtBu)(Me2Pyr)(py) (3) (ArtBu=O‐2,6‐tBu2‐4‐MeC6H2, Me2Pyr=2,5‐dimethylpyrrolyl) and study their grafting onto the surface of partially dehydroxylated silica with the aim to prepare 4‐coordinate Ti imido aryloxide surface species. Study of the resulting materials with IR, solid‐state NMR, elemental and mass balance analyses demonstrates that grafting of bis‐aryloxide complex 2 leads to a predominant formation of silica‐supported Ti amide (≡SiO)Ti(NHtBu)(OArtBu)2(py) resulting from the protonation of the imido ligand with the surface silanols and only a smaller fraction of the desired imido species (≡SiO)Ti(=NtBu)(OArtBu)(py). The use of the tailored complex 3 where one of the aryloxides is replaced with a more reactive pyrrolyl ligand significantly increases the selectivity of grafting leading to the formation of the Ti imido aryloxide (≡SiO)Ti(=NtBu)(OArtBu)(py) as major surface species. The obtained materials show high activity in catalytic oxo/imido heterometathesis supporting the previously proposed hypothesis that electron‐donating environments are favorable for this transformation. [ABSTRACT FROM AUTHOR]

The molecular approach to single-site and nanoparticle-based heterogeneous catalysts relies on a stringent control over the surface chemistry, enabled by the judicious choice of dehydroxylated supports and tailored organometallic precursors. Aided by the advanced characterization methods, the field of surface organometallic chemistry (SOMC) has provided molecular-level insights into the mechanism and the nature of active sites of various industrial catalysts. The development of SOMC over the last decades yielded supported catalysts outperforming their homogeneous precursors and provided design principles for catalyst development. Applying the rational structure-activity approach of homogeneous catalysis to the surface species leads to further advances of SOMC, including functional materials for sustainable chemistry, energy storage and imaging, to mention just a few. Graphical Abstract: [ABSTRACT FROM AUTHOR]

[Display omitted] • Summary of stoichiometric oxo/imido heterometathesis reactions of imido complexes. • Current progress in the development of catalytic oxo/imido heterometathesis. • SOMC towards the design of well-defined silica-supported oxo and imido complexes. Oxo/imido heterometathesis is a class of reactions that interconvert terminal transition metal oxo and imido complexes via [2 + 2] cycloaddition/cycloreversion with heteroolefins and heterocumulenes containing oxo and imino groups. In this review we summarize the literature examples of stoichiometric oxo/imido heterometathesis reactions of imido complexes with different oxo substrates and discuss the current progress in the development of catalytic oxo/imido heterometathesis. In particular, we show how application of Surface Organometallic Chemistry approach allows preparation of highly efficient oxo/imido heterometathesis catalysts based on well-defined silica-supported early transition metal oxo and imido complexes. [ABSTRACT FROM AUTHOR]

Grafting the molecular complex (MesN)2Mo(CH2CMe2Ph)2 onto the surface of silica dramatically enhances its catalytic activity in the oxo/imido heterometathesis reaction of N-sulfinylamines with carbonyl compounds. [ABSTRACT FROM AUTHOR]

5‐Coordinated methoxybenzylidene complexes M(=NAr)(=CH−C6H4−o‐OMe)(OtBuF3)2 (Ar=2,6‐iPr2C6H3; tBuF3=CMe2(CF3)) of Mo (1mMo) and W (1mW) were synthesized by cross‐metathesis from the corresponding neophylidene/neopentylidene precursors and o‐methoxystyrene. 1mMo and 1mW were grafted onto the surface of silica partially dehydroxylated at 700 °C to give well‐defined silica‐supported alkylidenes (≡SiO)M(=NAr)(=CH−C6H4−o‐OMe)(OtBuF3) (M=Mo (1Mo), W (1W)). Supported methoxybenzylidene complexes were tested in metathesis of cis‐4‐nonene, 1‐nonene, and ethyl oleate, and compared to their molecular precursors and supported classical analogs (≡SiO)M(=NAr)(=CHCMe2R)(OtBuF3) (M=Mo, R=Ph (2Mo), M=W, R=Me (2W)). Both grafted complexes 1Mo and 1W show significantly better performance as compared to their molecular precursors 1mMo and 1mW but are less efficient than the classical 4‐coordinated alkylidenes 2Mo and 2W. Noteworthy, both 1Mo and 1W can reach equilibrium conversion in metathesis of cis‐4‐nonene at catalyst loadings as low as 50 ppm. [ABSTRACT FROM AUTHOR]

Here we present our observations on a peculiar kinetic behavior observed at low catalyst loadings for the metathesis of internal olefins on a highly active silica‐supported tungsten oxo alkylidene prepared through surface organometallic chemistry (SOMC). The observed kinetic profile is comprised of two consecutive regimes, which support the presence of two different active sites on the surface of such catalysts. We propose that the more active site is operational in the beginning of the reaction but deactivates very fast, and the second one initiates over time due to the presence of ethylene formed subsequently under the reaction conditions. A combination of spectroscopic techniques and computations was used to identify the possible nature of these sites. Solid‐state NMR, EXAFS and DFT calculations are consistent with the esence of two distinct surface species that likely originate from the occurrence of slightly different local environments on the surface, that is, metal sites with a different number of nearby siloxane bridges. This data highlights the effects that may arise from the amorphous nature of the supports like silica and the difficulties to obtain truly single‐site catalysts – one of the ultimate goals of SOMC. [ABSTRACT FROM AUTHOR]