Dehydrogenation of Alkanes and Aliphatic Groups by Pincer-Ligated Metal Complexes

Abstract

The alkyl group is the most common component of organic molecules and the most difficult to selectively functionalize. The development of catalysts for dehydrogenation of alkyl groups to give the corresponding olefins could open almost unlimited avenues to functionalization. Homogeneous systems, or more generally systems based on molecular (including solid-supported) catalysts, probably offer the greatest potential for regio- and chemoselective dehydrogenation of alkyl groups and alkanes. The greatest progress to date in this area has been achieved with pincer-ligated transition-metal-based catalysts; this and related chemistry are the subject of this review. Chemists are still far from achieving the most obvious and perhaps most attractive goal in this area, the dehydrogenation of simple alkanes to yield alkenes (specifically monoenes) with high yield and selectivity. Greater progress has been made with tandem catalysis and related approaches in which the initial dehydrogenated product undergoes a desirable secondary reaction. Also reviewed is the substantial progress that has been made in the closely related area of dehydrogenation of alkyl groups of substrates containing heteroatoms.

One‐Pot Cooperation of Single‐Atom Rh and Ru Solid Catalysts for a Selective Tandem Olefin Isomerization‐Hydrosilylation Process

“…Reaction yields could be increased by af actor of 3, and the conversion extended to further internal olefins such as 4-octene,b y increasing the reaction temperature to 413 K, in this case with comparatively lower product regioselectivities,y et in excess of 80 %( entries 14 and 15). This catalytic system proved also efficient to selectively convert complex mixtures of terminal and internal olefins into terminal organosilanes.Amixture of 8-bromooctene isomers,generated by isomerization of the corresponding a-olefin (8-bromo-1-octene) with 1.0 Ru/CeO 2 ,w as converted with 91 %s electivity to the terminal 1,1,1-triethyl-8bromooctylsilane.S imilarly high regioselectivities were also achieved from industrially relevant olefin mixtures,representative for output streams from mild-temperature paraffin dehydrogenation processes, [4] and olefin oligomerization/ metathesis operations,a si nt he commercial Shell Higher Olefin Process . [10,23] In all cases,the cooperation of Ru/CeO 2 and Rh/CeO 2 single-atom catalysts in tandem led to ahighly selective (> 95 %) production of terminal organosilanes ( Table 2, entries 18 and 19).…”

Synthesis and Reactivity of Cationic Boron Complexes Distorted by Pyridine‐based Pincer Ligands: Isolation of a Photochemical Hofmann–Martius‐type Intermediate

“…[11] Due to their tunability, control over coordination sites and thermal stability, [12] various pincer-type transition metal complexes are very successful catalysts in organic synthesis. [13] Many pincer catalysts activate substrate H À X bonds via metal-ligand cooperation, [14] which does not require a change in metal oxidation state. We and others have explored cooperative H À X bond activations at chelates of redox-inert elements such as boron in complexes of bidentate ligands.…”

Acridine Variations for Coordination Chemistry

“…The development of new phosphine frameworks, enabling the fine-tuning of electronics and sterics at the supported metal center, has enabled remarkable recent advances in transition metal catalysis. [1] Pincer ligands in particular have proven valuable to the generation of reactive metal sites, [2] allowing advances in alkane activation [3] and dinitrogen fixation, [4] as well as in transformations of carbon dioxide. [5] Pursuing new pathways in CO 2 chemistry, [6] we became interested in acridine-based pincers.…”