We report diverse C–N cross-coupling reactions of aryl thianthrenium salts that are formed site-selectively by direct C–H functionalization. The scope of N-nucleophiles ranges from primary and secondary alkyl and aryl amines to various N-containing heterocycles, and the overall transformation is applicable to late-stage functionalization of complex, drug-like small molecules.

Herein, we report a two‐step process forming arene C−O bonds in excellent site‐selectivity at a late‐stage. The C−O bond formation is achieved by selective introduction of a thianthrenium group, which is then converted into C−O bonds using photoredox chemistry. Electron‐rich, ‐poor and ‐neutral arenes as well as complex drug‐like small molecules are successfully transformed into both phenols and various ethers. The sequence differs conceptually from all previous arene oxygenation reactions in that oxygen functionality can be incorporated into complex small molecules at a late stage site‐selectively, which has not been shown via aryl halides.

A library of 29 homologous Ru-based olefin metathesis catalysts has been tested for ethenolysis of cyclic olefins toward the goal of selectively forming α,ω-diene using cis-cyclooctene as a prototypical substrate. Dissymmetry at the N-heterocyclic carbene (NHC) ligand was identified as a key parameter for controlling the selectivity. The best-performing catalyst bearing an N-CF group significantly outperformed the benchmark second-generation Grubbs catalyst in the ethenolysis of cis-cyclooctene. Application of this optimal catalyst to the ethenolysis of various norbornenes allows the efficient synthesis of valuable diene intermediates in good yields. The observed ligand effect trends could be rationalized through univariate and multivariate parameter analysis involving steric and electronic descriptors of the NHC ligand in the form of the buried volume and the Se NMR chemical shift, in particular the σ component of the shielding tensor of [Se(NHC)] model compounds, respectively. Natural chemical shift analysis of this chemical shielding tensor shows that σ probes the π-acceptor property of the NHC ligand, the essential electronic parameter that drives the relative rate of degenerate metathesis and selectivity in ethenolysis with catalysts bearing dissymmetric NHC ligands.

Starting from N-trifluoromethyl benzimidazole (1), a series of N-trifluoromethyl benzimidazolium salts 2a–f·HA have been prepared and fully characterized. These were engaged in the formation of [Ir­(CO)2(NHC)­Cl], [Rh­(COD)­(NHC)­Cl], [Se­(NHC)], and [Au­(NHC)­Cl] derivatives. IR analysis of [Ir­(CO)2(NHC)­Cl] complexes revealed that the trifluoromethyl substituent on nitrogen significantly decreases the σ-donating ability of the carbene carbon. On the other hand, the π-acceptor property of these novel ligands is enhanced. Examination of the 77Se NMR resonance of [Se­(NHC)] adducts and the redox potentials of [Rh­(NHC)­(COD)­Cl] complexes further supports this assumption. In addition, the efficiency of these new N-trifluoromethyl NHC ligands was investigated in π-acidic Au­(I)-catalyzed hydroalkoxylation of cyclohexene. The gold complexes bearing NHCs 2a and 2c–e compete with [Au­(PPh3)­Cl] in terms of catalytic activity.

We report the synthesis of ruthenium metathesis catalysts containing unsymmetrical N-trifluoromethyl NHC ligands. These complexes have been fully characterized, and a Ru–F interaction has been identified in the solid state by X-ray crystallographic analysis for three catalysts with Ru–F distances between 2.629(2) and 2.652(2) Å. The influence of the N-trifluoromethyl NHC ligands on the initiation rates and activation parameters was studied. The activity of these catalysts was evaluated in benchmark olefin metathesis reactions and compared to the standard second-generation Grubbs catalyst. Remarkably, N-trifluoromethyl catalysts display an unusually high selectivity for the formation of terminal olefins (up to 90%) in the ethenolysis of ethyl oleate. Much improved selectivity is demonstrated for alternating copolymerization of cyclooctene and norbornene as well. These results underline the importance of electronic effects exerted by the NHC ligand.