Metal−ligand cooperation, in which metal and ligand participate in bond cleavage and formation, is gathering great attention in recent years. In contrast to the classical bond cleavage by active metal centers with spectator ligands, metal−ligand cooperation has enabled unprecedented reactivities. Especially, metal−ligand cooperative H−H bond cleavage has been extensively studied and applied to various catalysts. On the other hand, there are substantial efforts to expand the scope of the bond to be cleaved other than the H−H bond. This review summarizes the recent progress in the metal−ligand cooperative cleavages of Si−H, B−H, and C−H bonds and their catalytic applications.

C–H bond cleavage and formation is one of the most essential elementary reactions in organic chemistry. Herein, a heterolytic sp3 C–H bond reductive elimination from hydroxyCp dimethylplatinum­(IV) B is reported. Protonation of cyclopentadienone dimethylplatinum­(II) A afforded B via the protonation of the ligand. Successive C–H bond formation from the C anion of the methyl group and the H cation of the hydroxyCp group was observed in the presence of carboxylic acids or hydrogen chloride. The reaction was accompanied by the concurrent reduction of Pt­(IV) to Pt­(II). Experimental and theoretical investigations suggested that the mechanism for the C–H bond formation was acid-mediated metal–ligand cooperative outer-sphere reductive elimination.

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In contrast to conventional metal–ligand cooperative cleavage of a B−H bond, which provides a B cation on the ligand and an H anion on the metal, we report herein the umpolung of B−H bonds by novel cyclopentadienone iridium complexes. The B−H bonds of 4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane (HBpin) and 1,8‐naphthalenediaminatoborane (HBdan) were cleaved to give a B anion on the metal and an H cation on the phenolic oxygen atom of the ligand. Mechanistic investigation by DFT calculations revealed that the alkoxycarbonyl‐substituted cyclopentadienone ligand facilitated deprotonation from Ir−H after oxidative addition of the B−H bond to give the umpolung product. The generated boryliridium complex was found to undergo borylation of an allyl halide in the presence of base, thus showing the nucleophilic nature of the boron atom.

The cleavage of silicon−hydrogen bonds to generate silicon-containing metal complexes has played an essential role in the preparation of organosilicon compounds. Herein, we report the reaction of cyclopentadienone iridium complex 1 with hydrosilanes to afford hydroxycyclopentadienyl iridium silyl complexes 4 via the umpolung of the Si−H bond. The nucleophilicity of the Ir−Si bond in the resulting complex was demonstrated in the reaction with an allyl halide and ethyl acrylate. Furthermore, a silylene complex was formed from hydroxycyclopentadienyl silyliridium complex 4 via the formal reductive elimination of the C−H bond at the silicon center to release benzene. The silylene complex synthesized from tricarbylsilane showed ambiphilic reactivities, which are consistent with the classical reactivities of silylenes.

Oxidative addition reactions of C−H bonds that generate metal−carbon-bond-containing reactive intermediates have played essential roles in the field of organometallic chemistry. Herein, we prepared a cyclopentadienone iridium(I) complex 1 designed for oxidative C−H bond additions. The complex cleaves the various sp 2 and sp 3 C−H bonds including those in hexane and methane as inferred from their H/D exchange reactions. The hydroxycyclopentadienyl(nitromethyl)iridium(III) complex 2 was formed when the complex was treated with nitromethane, which highlights this elementary metal−ligand cooperative C−H bond oxidative addition reaction. Mechanistic investigations suggested the C−H bond cleavage is mediated by polar functional groups in substrates or another iridium complex. We found that ligands that are more electron-deficient lead to more favorable reactions, in sharp contrast to classical metal-centered oxidative additions. This trend is in good agreement with the proposed mechanism, in which C−H bond cleavage is accompanied by two-electron transfer from the metal center to the cyclopentadienone ligand. The complex was further applied to catalytic transfer-dehydrogenation of tetrahydrofuran (THF).

The borylation of Csp3‐H bonds is a challenging transformation that is typically restricted to transition metal catalysis. Herein, we report the site‐selective metal‐free Csp3–H borylation of saturated cyclic amines. It is possible to selectively borylate piperidine derivatives at the α or β positions according to the reaction conditions. The mechanism was supported by NMR spectroscopy, calorimetry experiments and density functional theory (DFT) computations. It suggests that the piperidine is dehydrogenated by complexation with BBr3 to produce an enamine intermediate, which is in turn borylated at either the α or β position according to the reaction conditions.

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