C–H Polyaddition of Dimethoxyarenes to Unconjugated Dienes by Rare Earth Catalysts

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation. In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate. Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it. Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure. The schemes feature typical substrates used, the products obtained as well as the required reaction conditions. Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness. The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them. Accordingly, this review should be of particular interest also for scientists from industrial R&D sector. Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date.

Efficient and selective catalysis for hydrogenation and hydrosilation of alkenes and alkynes with PNP complexes of scandium and yttrium

Scandium and yttrium congeneric complexes, supported by a monoanionic PNP ligand, were studied as catalysts for alkene hydrogenation and hydrosilation, and alkyne semihydrogenation and semihydrosilation. The yttrium congener was found to be much more active in all cases, but this greater activity is accompanied by more rapid catalyst decomposition and therefore higher total yields for some of the reactions with the scandium catalyst. Calculations indicate that the reactions may proceed via σ-bond metathesis of the alkyl complexes to form metal hydride intermediates into which alkenes/alkynes insert.

Heteroatom-assisted olefin polymerization by rare-earth metal catalysts

Heteroatom-functionalized polyolefins are of fundamental interest and practical importance. This has spurred investigations of the copolymerization of polar and nonpolar olefins. We report the first syndiospecific polymerization of a series of heteroatom-containing α-olefins and their copolymerization with ethylene catalyzed by half-sandwich rare-earth complexes. We have found that the interaction between a heteroatom in a functional α-olefin monomer and a rare-earth metal catalyst can significantly raise the olefin polymerization activity and thereby promote its copolymerization with ethylene. By using this heteroatom-assisted olefin polymerization (HOP) strategy, we have successfully synthesized a series of heteroatom (O, S, Se, N, and P)-functionalized polyolefins with high molecular weights and controllable functional monomer contents. The mechanistic aspect of the HOP process has been elucidated by computational studies. We expect that our findings will guide the design of new catalyst systems for the synthesis of various desired functional polyolefins.

Preparation of diethylenetriamine-modified magnetic chitosan nanoparticles for adsorption of rare-earth metal ions

The development of a sustainable method to conveniently separate rare-earth metal ions remains a challenge waiting for breakthrough in numerous of advanced technologies.

Scandium-catalysed intermolecular hydroaminoalkylation of olefins with aliphatic tertiary amines

A homoleptic scandium trialkyl complex in combination with a borate compound served as an excellent catalyst for the C-H addition of aliphatic tertiary amines to olefins. This highly regiospecific, 100% atom efficient C-H bond alkylation reaction was applicable to a wide variety of tertiary amines and olefins, including functionalised styrenes and unactivated α-olefins. This work represents the first example of rare-earth catalysed olefin hydroaminoalkylation and also the first example of catalytic C-H addition of aliphatic tertiary amines to olefins with any catalyst.