The Effect of the cis-donor in pincer ligands on hydrogenolysis of Pd-OH: A DFT study

Insertion of Molecular Oxygen into a Gold(III)-Hydride Bond

The use of molecular oxygen as an oxidant in chemical synthesis has significant environmental and economic benefits, and it is widely used as such in large-scale industrial processes. However, its adoption in highly selective homogeneous catalytic transformations, particularly to produce oxygenated organics, has been hindered by our limited understanding of the mechanisms by which O2 reacts with transition metals. Of particular relevance are the mechanisms of the reactions of oxygen with late transition metal hydrides as these metal centers are better poised to release oxygenated products. Homogeneous catalysis with gold complexes has markedly increased, and herein we report the synthesis and full characterization of a rare AuIII-H, supported by a diphosphine pincer ligand (tBuPCP = 2,6-bis(di-tert-butylphosphinomethyl)benzene). [(tBuPCP)AuIII-H]+ was found to cleanly react with molecular oxygen to yield a stable AuIII-OOH complex that was also fully characterized. Extensive kinetic studies on the reaction via variable temperature NMR spectroscopy have been completed, and the results are consistent with an autoaccelerating radical chain mechanism. The observed kinetic behavior exhibits similarities to that of previously reported PdII-H and PtIV-H reactions with O2 but is not fully consistent with any known O2 insertion mechanism. As such, this study contributes to the nascent fundamental understanding of the mechanisms of aerobic oxidation of late metal hydrides.

Hydrogenolysis of Dinuclear PCNR Ligated PdII μ-Hydroxides and Their Mononuclear PdII Hydroxide Analogues

The hydrogenolysis of mono- and dinuclear Pd^II hydroxides was investigated both experimentally and computationally. It was found that the dinuclear μ-hydroxide complexes {[(PCN^R )Pd]₂ (μ-OH)}(OTf) (PCN^H =1-[3-[(di-tert-butylphosphino)methyl]phenyl]-1H-pyrazole; PCN^Me =1-[3-[(di-tert-butylphosphino)methyl]phenyl]-5-methyl-1H-pyrazole) react with H₂ to form the analogous dinuclear hydride species {[(PCN^R )Pd]₂ (μ-H)}(OTf). The dinuclear μ-hydride complexes were fully characterized, and are rare examples of structurally characterized unsupported singly bridged μ-H Pd^II dimers. The {[(PCN^Me )Pd]₂ (μ-OH)}(OTf) hydrogenolysis mechanism was investigated through experiments and computations. The hydrogenolysis of the mononuclear complex (PCN^H )Pd-OH resulted in a mixed ligand dinuclear species [(PCN^H )Pd](μ-H)[(PCC)Pd] (PCC=a dianionic version of PCN^H bound through phosphorus P, aryl C, and pyrazole C atoms) generated from initial ligand "rollover" C-H activation. Further exposure to H₂ yields the bisphosphine Pd⁰ complex Pd[(H)PCN^H ]₂ . When the ligand was protected at the pyrazole 5-position in the (PCN^Me )Pd-OH complex, no hydride formed under the same conditions; the reaction proceeded directly to the bisphosphine Pd⁰ complex Pd[(H)PCN^Me ]₂ . Reaction mechanisms for the hydrogenolysis of the monomeric and dimeric hydroxides are proposed.

Synthesis, structural properties and reactivity of ruthenocene-based pincer Pd(ii) tetrahydroborate

Non-covalent interactions determine the structure, crystal packing and reactivity of isolated ruthenocene-based pincer Pd(ii) complexes. Bifurcate dihydrogen-bonded complexes are active intermediates of tetrahydroborate alcoholysis.