C–H and O2 Activation at a Pt(II) Center Enabled by a Novel Sulfonated CNN Pincer Ligand

Oxidative Addition of a Hypervalent Iodine Compound to Cycloplatinated(II) Complexes for the C-O Bond Construction: Effect of Cyclometalated Ligands

The complex [PtMe(Obpy)(OAc)₂(H₂O)], 2a, Obpy = 2,2'-bipyridine N-oxide, is prepared through the reaction of [PtMe(Obpy)(SMe₂)], 1a, by 1 equiv of PhI(OAc)₂ via an oxidative addition (OA) reaction. Pt(IV) complex 2a attends the process of C-O bond reductive elimination (RE) reaction to form methyl acetate and corresponding Pt(II) complex [Pt(Obpy)(OAc)(H₂O)], 3a. The kinetic of OA and RE reactions are investigated by means of different spectroscopies. The obtained results show that the reaction rates of OA step of 1a are faster than its analogous complex [PtMe(ppy)(SMe₂)], 1b, ppy = 2-phenylpyridine. The density functional theory (DFT) calculations signify that the OA reaction initiated by a nucleophilic attack of the platinum(II) central atom of 1b on the iodine(III) atom while it had commenced by a nucleophilic substitution reaction of coordinated SMe₂ in 1a with a carbonyl oxygen atom of PhI(OAc)₂. Our calculation revealed that the key step for 1a is an acetate transfer from the I(III) to Pt(II) through a formation of square pyramidal iodonium complex. This can be attributed to the more electron-withdrawing character of Obpy ligand than to ppy which reduces the nucleophilicity of Pt atom in 1a. Furthermore, 2a with electron-withdrawing Obpy ligand prone to C-O bond formation faster than complex [PtMe(ppy)(OAc)₂(H₂O)], 2b, with an electron-rich ppy ligand which conforms to the anticipation that REs occur faster on electron-poor metal centers.

Late-Stage β-C(sp3)-H Deuteration of Carboxylic Acids

Carboxylic acids are highly abundant in bioactive molecules. In this study, we describe the late-stage β-C(sp³)-H deuteration of free carboxylic acids. On the basis of the finding that C-H activation with our catalysts is reversible, the de-deuteration process was first optimized. The resulting method uses ethylenediamine-based ligands and can be used to achieve the desired deuteration when using a deuterated solvent. The reported method allows for the functionalization of a wide range of free carboxylic acids with diverse substitution patterns, as well as the late-stage deuteration of bioactive molecules and related frameworks and enables the functionalization of nonactivated methylene β-C(sp³)-H bonds for the first time.

A serendipitous self-assembly synthesis of CNN–Pt pincer complexes

A serendipitous one pot self-assembly synthesis of hydride CNN–Pt(iv) pincer complexes was achieved, which involves a formal C–H bond activation, with an earlier C–N bond formation via C–Br bond excision, instead of the expected rollover complex.

Preparation and characterization of terdentate [C,N,N] acetophenone and acetylpyridine hydrazone platinacycles: a DFT insight into the reaction mechanism

The reaction of N-ortho-chlorophenyl-substituted acetylpyridine hydrazones (a and d) with K₂[PtCl₄] (n-butanol/water, 100 °C) gave mononuclear complexes 1a and 1d with the ligands as [N,N] bidentate. In contrast, the reaction of N-phenyl or N-meta-chlorophenyl hydrazones (b and c, respectively) under analogous reaction conditions gave the cycloplatinated species 2b and 2c with the ligand as [C,N,N] terdentate. The treatment of the mononuclear complexes 1a and 1d with NaOAc (n-butanol, 100 °C) gave the corresponding cycloplatinated complexes 2a and 2d. Acetophenone hydrazone platinacycle 2e was prepared in a similar fashion and its reaction with tertiary mono- and triphosphines gave mono- or trinuclear species depending on the reaction conditions. The X-ray crystal structures of some of these complexes showed interesting π-π slipped stacking interactions between metallacyclic rings which, according to NCI analyses, showed an aromatic character. With an aim to rationalize the different reactivities shown by acetylpyridine hydrazones and the precise role of the acetate anion, the energy profiles for the three main steps of cycloplatination (iminoplatinum complex formation, chelation and cyclometallation) have been determined by using the DFT (M06) methods. Calculations indicate that the cycloplatination of 1b proceeds via electrophilic substitution, involving the direct replacement of the chloride anion at the Pt(ii) centre with the N-phenyl moiety as the rate-determining step, to give an agostic intermediate 5b+ that, subsequently, leads to the elimination of a proton as hydrogen chloride. When present as an "external" base, acetate enters the coordination sphere around the Pt(ii) centre and facilitates hydrazone N-H deprotonation and electrophilic C-H activation through a dissociative route, leading to a Wheland-type σ-complex intermediate 9ac.