3 Ruthenium-Catalyzed Azide–Alkyne Cycloaddition (RuAAC)

Under ruthenium catalysis, 1,5-disubstituted 1,2,3-triazoles can be accessed with high selectivity from terminal alkynes and organic azides via a ruthenium-catalyzed azide–alkyne cycloaddition (RuAAC) reaction. These conditions also allow the use of internal alkynes, providing access to 1,4,5-trisubstituted 1,2,3-triazoles. This chapter reviews the scope and limitations of the RuAAC reaction, as well as selected applications. A brief mention of azide–alkyne cycloaddition reactions catalyzed by other metals is also included.

Triazole-Enabled Ruthenium(II)carboxylate-Catalyzed C–H Arylation with Electron-deficient Aryl Halides

The triazole-directed direct C–H arylation of arenes with electron-deficient aryl halides and a synthetically-useful pyrimidyl chloride was achieved via ruthenium catalysis. Our novel strategy provides operationally-simple and environmentally-benign access to highly functionalized heteroarenes, avoiding the use strong organometallic bases. Detailed studies revealed a significant effect of the phosphine ligand, thus allowing for the reaction to occur with excellent levels of chemo- and position-selectivity.

Remote C–H Functionalizations by Ruthenium Catalysis

Synthetic transformations of otherwise inert C–H bonds have emerged as a powerful tool for molecular modifications during the last decades, with broad applications towards pharmaceuticals, material sciences and crop protection. Consistently, a key challenge in C–H activation chemistry is the full control of site-selectivity. In addition to substrate control through steric hindrance or kinetic acidity of C–H bonds, one important approach for the site-selective C–H transformation of arenes is the use of chelation-assistance through directing groups, therefore leading to proximity-induced ortho-C–H metalation. In contrast, more challenging remote C–H activations at the meta- or para-positions continue to be scarce. Within this review, we demonstrate the distinct character of ruthenium catalysis for remote C–H activations until March 2021, highlighting among others late-stage modifications of bio-relevant molecules. Moreover, we highlight important mechanistic insights by experiments and computation, highlighting the key importance of carboxylate-assisted C–H activation with ruthenium(II) complexes.

Hydrogenation and Hydrogenolysis with Ruthenium Catalysts and Application to Biomass Conversion

With the rising emphasis on efficient and highly selective chemical transformations, the field of ruthenium-catalysed hydrogenation and hydrogenolysis reactions has grown tremendously over recent years. The advances are triggered by the detailed understanding of the catalytic pathways that have enabled researchers to improve known transformations and realise new transformations in biomass conversion. Starting with the properties of ruthenium, this chapter introduces the concept of the catalytic function as a basis for rational design of ruthenium catalysts. Emphasis is placed on discussing the principles of dissociative adsorption of hydrogen. The principles are then applied to the conversion of typical biomolecules such as cellulose, hemicellulose and lignin. Characteristic features make ruthenium catalysis one of the most outstanding tools for implementing sustainable chemical transformations.

Visible-light enabled room-temperature dealkylative imidation of secondary and tertiary amines promoted by aerobic ruthenium catalysis

A photoredox dealkylative imidation of tertiary and secondary amines with sulfonyl azide facilitated by aerobic ruthenium-catalysis to afford sulfonyl amidine at room temperature is reported.