Patrick Melvin

The robust, high-valent Ni^IV complex [(Py)₂Ni^IVF₂(CF₃)₂] (Py=pyridine) was synthesized and fully characterized by NMR spectroscopy, X-ray diffraction, and elemental analysis. It reacts with aromatic compounds at 25 °C to form the corresponding benzotrifluorides in nearly quantitative yield. The monomeric and dimeric Ni^IIICF₃ complexes 2⋅Py and 2 were identified as key intermediates, and their structures were unambiguously determined by EPR spectroscopy and X-ray diffraction. Preliminary kinetic studies in combination with the isolation of reaction intermediates confirmed that the C−H bond-breaking/C−CF₃ bond-forming sequence can occur both at Ni^IVCF₃ and Ni^IIICF₃ centers.

The robust, high-valent complex [(Py)₂Ni^IVF₂(CF₃)₂] (Py=pyridine) was isolated on gram scale. This unique Ni^IVCF₃ species reacts with aromatic compounds to yield benzotrifluorides in >90 % yield. The mechanism of the reaction was comprehensively investigated, and the involvement of unprecedented Ni^IIICF₃ intermediates was confirmed.

We have prepared and fully characterized two isomers of [Ir^IV(dpyp)₂] (dpyp=meso-2,4-di(2-pyridinyl)-2,4-pentanediolate). These complexes can cleanly oxidize to [Ir^V(dpyp)₂]⁺, which to our knowledge represent the first mononuclear coordination complexes of Ir^V in an N,O-donor environment. One isomer has been fully characterized in the Ir^V state, including by X-ray crystallography, XPS, and DFT calculations, all of which confirm metal-centered oxidation. The unprecedented stability of these Ir^V complexes is ascribed to the exceptional donor strength of the ligands, their resistance to oxidative degradation, and the presence of four highly donor alkoxide groups in a plane, which breaks the degeneracy of the d-orbitals and favors oxidation.

A robust ligand and a rare oxidation state: [Ir^IV(dpyp)₂] cleanly oxidizes to [Ir^V(dpyp)₂]⁺, the first mononuclear example of Ir^V in an N,O-donor environment. Full characterization of the Ir^V species, including by X-ray crystallography in one case, allows exploration of this rare oxidation state.