A silica-supported titanium catalyst for heterogeneous hydroamination and multicomponent coupling reactions

Readily available Ti-based in situ catalytic system for oxo/imido heterometathesis

We investigate Ti(NEt2)4 supported on silica dehydroxylated at 700 °C as an easily accessible pre-catalyst for oxo/imido heterometathesis reactions. Being activated with TolNH2, the supported Ti amide (SiO)Ti(NEt2)3 (1) demonstrates catalytic activity in the imidation of ketones with N-sulfinylamines comparable with the most active previously described well-defined imido catalyst (SiO)Ti(NtBu)(Me2Pyr)(py)2 (2) (Me2Pyr = 2,5-dimethylpyrrolyl), which implies the in situ formation of surface imido species in this system. The materials obtained via treatment of 1 with anilines (TolNH2 (1a) and p-MeOC6H415NH2 (1b)) were studied with IR, EA and 1H, 13C, 15N and 2D solid-state NMR, although the proposed imido intermediate has not been detected, pointing towards tris-amides (SiO)Ti(NHC6H4X)3 (X = Me, OMe) being the major surface species in the isolated materials 1a and 1b. The system 1/TolNH2 was tested in a range of imidation reactions and demonstrated excellent performance for express high-yielding preparation of ketimines, formamidines, lactone imidates and sulfurdiimines, making it a convenient alternative to the well-defined supported Ti imido catalysts.

Catalytic Approaches to Multicomponent Reactions: A Critical Review and Perspectives on the Roles of Catalysis

In this review, we comprehensively describe catalyzed multicomponent reactions (MCRs) and the multiple roles of catalysis combined with key parameters to perform these transformations. Besides improving yields and shortening reaction times, catalysis is vital to achieving greener protocols and to furthering the MCR field of research. Considering that MCRs typically have two or more possible reaction pathways to explain the transformation, catalysis is essential for selecting a reaction route and avoiding byproduct formation. Key parameters, such as temperature, catalyst amounts and reagent quantities, were analyzed. Solvent effects, which are likely the most neglected topic in MCRs, as well as their combined roles with catalysis, are critically discussed. Stereocontrolled MCRs, rarely observed without the presence of a catalytic system, are also presented and discussed in this review. Perspectives on the use of catalytic systems for improved and greener MCRs are finally presented.

Palladium oxide-decorated mesoporous silica on graphene oxide nanosheets as a heterogeneous catalyst for the synthesis of β-substituted indole derivatives

In this work, an efficient and facile strategy has been adopted for the stepwise synthesis of the RGO-MSiO2/PdO hybrid nanomaterial (HY-NM). Herein, a hybrid nanostructure of mesoporous silica over graphene oxide (GO) sheets has been developed followed by immobilizing palladium oxide nanoparticles (PdO NPs), and then it has been utilized for catalyzing a multicomponent reaction (MCR). To authenticate the successful synthesis of the HY-NM and successive immobilization of PdO NPs, various physicochemical characterization techniques were utilized such as SEM, EDAX, HR-TEM, HR-XRD, TGA, BET, FT-IR, and XPS analysis. The activity of the HY-NM has been determined by performing the catalyst-mediated synthesis of β-substituted indole derivatives (yield 90-98%). The excellent catalytic activity of the prepared HY-NM could be observed due to its high surface area and large porosity, which facilitates the penetration and interaction of reactant molecules with the catalytic active species. This protocol eliminates the requirement of further purification after the isolation of the product from the reaction mixture. The ease of handling, recyclability of the catalyst, and simple work-up procedure are the main features of this protocol. The synthesized HY-NM could be recycled for multiple catalytic cycles making it a very effective heterogeneous catalyst.

Generation of Masked TiII Intermediates from TiIV Amides via β-H Abstraction or Alkyne Deprotonation: An Example of Ti-Catalyzed Nitrene-Coupled Transfer Hydrogenation

Simple Ti amide complexes are shown to act as sources for masked Ti^II intermediates via several pathways, as demonstrated through the investigation of a unique Ti-catalyzed nitrene-coupled transfer hydrogenation of 3-hexyne. This reaction proceeds through reduction of azobenzene by a masked Ti^II catalyst, wherein both amines and 3-hexyne can serve as the hydrogen source/reductant for Ti by forming putative titanaziridines via β-H abstraction or putative titanacyclopentynes via protonolysis, respectively.

Titanium catalysis for the synthesis of fine chemicals – development and trends

Atlas as a Titan(ium) is holding the earth-abundant chemistry world. Titanium is the second most abundant transition metal, is a key player in important industrial processes (e.g. polyethylene) and shows much promise for diverse applications in the future.