Yosi Kratish, Arseni Kostenko, Alexander Kaushansky, Boris Tumanskii, Dmitry Bravo-Zhivotovskii* and Yitzhak Apeloig*
Platinum is one of the catalytically most versatile transition metal with numerous applications in the fields of organic synthesis, materials synthesis and medicine. Platinum complexes are efficient catalysts in a wide range of reactions, e.g. hydroformylation, hydrosilylation, hydrogenation and polymerization. Platinum complexes are also frequently employed in cancer therapy; approximately half of all patients who receive anticancer chemotherapy are treated with platinum drugs. Consequently, an enormous amount of information is available on the structures and reactivity of platinum complexes. Most of the knowledge is for diamagnetic, closed shell Pt(0), Pt(II), and Pt(IV) complexes. Much less is known about the structures, reactivity, and physical properties of Pt(I) and Pt(III) paramagnetic complexes, despite their postulated role in anticancer activity of platinum based drugs and as intermediates in several chemical transformations. Recently, different Pt(III) paramagnetic complexes were reported. In contrast, very little is known about open-shell Pt(I) complexes and only unstable short-lived Pt(I) intermediate species were detected in some electrochemical or pulse radiolysis reactions, but these proposed Pt(I) species were not characterized spectroscopically.
In this paper, we report the generation of the first room temperature persistent platinum(I) centered radical (1) and its characterization by EPR spectroscopy, chemical trapping experiments and Density Functional Theory (DFT) calculations. The platinum(I) centered radical (1) was generated by homolytic cleavage of a Pt-HgSiR3 bond of a mercury substituted platinum(II) complex (2) (Scheme, step a). The Pt(I) radical is persistent with a half-life of 3 days at 300 K. Further support for the Pt(I) radical is provided by direct chemical trapping experiments. Thus, addition of TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxyl) to 1 leads to disappearance of the EPR signals and formation of the expected platinum-TEMPO adduct 3 (Scheme, path b),
According to the EPR spectra and the DFT calculations, 1 has a T-shaped geometry and 56% of the electron spin density is localized in a Pt(spxpydx2-y2) type orbital and 19% and 8% of the spin density are delocalized to the trans-P atom and Hg, respectively (Figure). This is the first spectroscopic observation of a metal-centered Pt(I) radical.
The research was carried by PhD students: Yosi Kratish (main author) , Arseni Kostenko, Alexander Kaushansky; research associates: Dr. Boris Tumanskii and Dr. Dmitry Bravo-Zhivotovskii, in the group of Prof. Yitzhak Apeloig.
This study was published in Angewandte Chemie International Edition, 57, 8275-8279, 2018 and was selected as a VIP paper (very important paper).