Reaction of 2-Methylanisole with TpMe2Ir(C6H5)2(N2): A Comprehensive Set of Activations

Radical-Friedel-Crafts benzylation of arenes with benzyl ethers over 2H-MoS2: ether cleavage into carbon- and oxygen-centered radicals

The selective activation of C-O ether bonds is an essential tool in organic synthesis and natural polymer depolymerization. However, the direct cleavage of the ether bond is still challenging work, especially breaking this inert and redox-neutral bond to provide one active carbon radical and another oxygen-centered fragment with oxidation capacity that can participate in the controllable radical reaction. We herein report that commercial 2H-MoS₂ with negligible acidity can efficiently catalyze the benzylation of arenes with benzyl ethers, and a new Radical-Friedel-Crafts mechanism is proposed, which is quite different from the strong acid-catalyzed Friedel-Crafts mechanism. With dibenzyl ether as the model benzylation reagent, 2H-MoS₂ can achieve the homolytic cleavage of the Bn-OR bond to generate the benzyl carbon radical and RO˙ species, identified by EPR measurement and radical trap experiments. The following radical-involved benzylation is confirmed by the Hammett results and a plausible pathway is proposed to clarify the Radical-Friedel-Crafts process. Heterogeneous 2H-MoS₂ can be consecutively used four times without regeneration and it offers 94-95% yields of 2-benzyl-1,4-dimethylbenzene from dibenzyl ether and p-xylene in 30 min at 140 °C. Furthermore, this mechanism can provide some inspiration to activate the ether bond and to utilize ether as an oxidant in C-H bond activation.

Activation of diverse carbon-heteroatom and carbon-carbon bonds via palladium(II)-catalysed β-X elimination

Chemists' ability to synthesize structurally complex, high-value organic molecules from simple starting materials is limited by methods to selectively activate and functionalize strong alkyl C(sp³) covalent bonds. Recent activity has focused on the activation of abundant C-O, C-N and C-C bonds via a mechanistic paradigm of oxidative addition of a low-valent, electron-rich transition metal. This approach typically employs nickel(0), rhodium(I), ruthenium(0) and iron catalysts under conditions finely tuned for specific, electronically activated substrates, sometimes assisted by chelating functional groups or ring strain. By adopting a redox-neutral strategy involving palladium(II)-catalysed C-H activation followed by β-heteroatom/carbon elimination, we describe here a catalytic method to activate alkyl C(sp³)-oxygen, nitrogen, carbon, fluorine and sulfur bonds with high regioselectivity. Directed hydrofunctionalization of the resultant palladium(II)-bound alkene leads to formal functional group metathesis. The method is applied to amino acid upgrading with complete regioselectivity and moderate to high retention of enantiomeric excess. Low-strain heterocycles undergo strong-bond activation and substitution, giving ring-opened products.

Recent advances in well-defined, late transition metal complexes that make and/or break C-N, C-O and C-S bonds

Chemical transformations that result in either the formation or cleavage of carbon-heteroatom bonds are among the most important processes in the chemical sciences. Herein, we present a review on the reactivity of well-defined, late-transition metal complexes that result in the making and breaking of C-N, C-O and C-S bonds via fundamental organometallic reactions, i.e. oxidative addition, reductive elimination, insertion and elimination reactions. When appropriate, emphasis is placed on structural and spectroscopic characterization techniques, as well as mechanistic data.

Platinum(0)-mediated C–O bond activation of ethers via an SN2 mechanism

DFT calculations demonstrate that Pt(0) bis(phosphine) complexes react with Ar^F–O–Me via an S_N2 mechanism to activate the O–CH₃ bond; experimental support is provided by reaction of Pt(PCy₃)₂ with 2,3,5,6-tetrafluoro-4-allyloxypyridine to form an aryloxide salt of [Pt(η³-allyl)(PCy₃)₂]⁺.

Oxidative addition of ether O-methyl bonds at a Pt(0) centre

Fluorinated (hetero)aromatic ethers undergo O–Me oxidative addition to form Pt–CH₃ complexes at Pt(PCyp₃)₂ in preference to C–H or C–F activation.

Chlorido[1-(2-oxidophen-yl)ethyl-idene][tris-(3,5-dimethyl-pyrazol-1-yl)hydro-borato]iridium(III) chloro-form monosolvate

In the title compound, [Ir(C₁₅H₂₂BN₆)(C₈H₇O)Cl]·CHCl₃, the Ir atom is formally trivalent and is coordinated in a slightly distorted octa­hedral geometry by three facial N atoms, one C atom, one O atom and one Cl atom. The Ir=C_carbene bond is strong and short and exerts a notable effect on the trans-Ir—N bond, which is about 0.10 Å longer than the two other Ir—N bonds. The chloro­form solvent mol­ecule is anchored via a weak C—H⋯Cl hydrogen bond to the Cl atom of the Ir complex mol­ecule. In the crystal, the constituents adopt a layer-like arrangement parallel to (010) and are held together by weak inter­molecular C—H⋯Cl hydrogen bonds, as well as weak Cl⋯Cl [3.498 (2) Å] and Cl⋯π [3.360 (4) Å] inter­actions. A weak intra­molecular C—H⋯O hydrogen bond is also observed.