Secondary ligand–metal interactions are decisive in many catalytic transformations. While arene–gold interactions have repeatedly been reported as critical structural feature in many high‐performance gold catalysts, we herein report that these interactions can also be replaced by Au⋅⋅⋅H−C hydrogen bonds without suffering any reduction in catalytic performance. Systematic experimental and computational studies on a series of ylide‐substituted phosphines featuring either a PPh3 (PhYPhos) or PCy3 (CyYPhos) moiety showed that the arene‐gold interaction in the aryl‐substituted compounds is efficiently compensated by the formation of Au⋅⋅⋅H−C hydrogen bonds. The strongest interaction is found with the C−H moiety next to the onium center, which due to the polarization results in remarkably strong interactions with the shortest Au⋅⋅⋅H−C hydrogen bonds reported to date. Calorimetric studies on the formation of the gold complexes further confirmed that the PhYPhos and CyYPhos ligands form similarly stable complexes. Consequently, both ligands showed the same catalytic performance in the hydroamination, hydrophenoxylation and hydrocarboxylation of alkynes, thus demonstrating that Au⋅⋅⋅H−C hydrogen bonds are equally suited for the generation of highly effective gold catalysts than gold‐arene interactions. The generality of this observation was confirmed by a comparative study between a biaryl phosphine ligand and its cyclohexyl‐substituted derivative, which again showed identical catalytic performance. These observations clearly support Au⋅⋅⋅H−C hydrogen bonds as fundamental secondary interactions in gold catalysts, thus further increasing the number of design elements that can be used for future catalyst construction.

Metal-ligand cooperation has emerged as a powerful concept in bond activation chemistry and catalysis. Here, both the metal and the ligand are directly involved in the bond breaking and bond formation processes, while in "classical" activation reactions the transformations solely take place at the metal centre. Several different types of cooperating ligand systems have been developed over the years and applied in catalysis. In this Feature Article, we will discuss the use of carbene ligands in cooperative bond activation reactions. We focus on two types of carbene complexes: mid and late transition metal carbene species (i) with PCcarbeneP pincer ligands and (ii) with strong anion-stabilizing α-substituents at the carbene carbon atom. These systems are active in a variety of bond activation reactions and have found first catalytic applications.

Bisylides and methandiides are two unique families of carbon bases that have found a variety of applications in recent years. Metalated ylides (yldiides) are the link between these types of compounds. Yet, only little is known about their properties, reactivities, and particularly their electronic structure. Here, we report the preparation of the metalated ylide [Ph3P-C-SO2Tol](-) (1) with different alkali metal counterions. The compounds have been studied by X-ray diffraction analysis and NMR spectroscopy and the first structures of a sodium and potassium yldiide are presented. The electronic structure of 1 was explored by DFT calculations confirming its relation with other divalent carbon species. Reactivity studies demonstrate the strong nucleophilicity of the yldiide and its capability to act both as a σ- and π-donor.

In the last 15 years, methandiide ligands have given access to a new class of carbene complexes with unique electronic properties. The metal-carbon interactions in these complexes cover a range of bonding situations, from highly polar interactions to metal-carbon double bonds. This flexibility has allowed the isolation of complexes with metals covering the whole periodic table, including metals that had long been reluctant to form multiple bonds with carbon atoms. Thus, recent years have seen the revelation of many unusual carbene species with interesting reactivities. In this microreview, we focus on the latest developments in the chemistry of me-

Cooperative B-H bond activation reactions with thio- and iminophosphoryl tethered ruthenium-carbene complexes are reported. The complexes show surprisingly different reactivities towards the commonly employed boranes CatBH, PinBH and BH ⋅LB as a result of different modes of metal-ligand cooperation. Although the iminophosphoryl system allows for selective 1,2-addition of the B-H bond across the Ru=C double bond, the sulfur analogue only delivers the 1,2-addition product for CatBH, whereas activation of BH and PinBH lead to further insertion reactions in one or more sides of the Ru-C-P-S-ring. The different reactivities can be explained by the differences in the electronics of the carbene complexes and the phosphoryl tether and by the Lewis acidities of the boranes. DFT calculations show that the mechanism of the reactions either proceeds by an addition across the Ru=C bond with different regioselectivities or across the Ru-S linkage.