Previous works by Shilov and Neumann showed that mediator (heteropolyacids) – containing systems may allow for aerobic methane CH functionalization by Pt(II) complexes, albeit at the expense of system stability and reaction selectivity. The careful design of more robust ligands that also allow for both CH and O2 activation at the metal center may mitigate these problems. Here we introduce a new class of sulfonated CNN pincer ligands that meet the above requirement. The parent ligand (6-phenylpyrid-2-yl)(2-pyridyl)methanesulfonate was cycloplatinated to form the CNN – ligated chloroplatinum(II) complex K[(CNN)PtCl]. Using perdeuterioarenes as substrates it was shown that both K[(CNN)PtCl] (1) and its aqua analog, (CNN)Pt(OH2) (2), catalyze efficient H/D exchange (TOF &gt; 10 h-1, TON 100 and TOF &gt; 60 h-1, TON 250, respectively, after 24 h) with trifluoroethanol (TFE) at 80 oC. While 1 is stable in TFE under O2, 2 was shown to undergo slow aerobic oxidation to produce (CNN)Pt(OCH2CF3)(OH), 3. Gratifyingly, when 2 is combined with benzene under an O2 atmosphere, or simply air, a much faster reaction occurs, yielding the new Pt(IV) complex (CNN)Pt(Ph)(OH), 4, as a result of consecutive C(sp2)-H and O2 activation. The formation of complex 4 is accompanied by oxidation of 2 to 3 and formation of a small amount of the Pt(II) complex (CNN’)Pt(OH2), 5, resulting from C-C coupling with the ligand. The mechanism of these transformations is analyzed using kinetics experiments and DFT calculations. Further tuning of the system to attenuate oxidation of 2 and to enable the catalytic aerobic CH functionalization of benzene and methane is also explored.

New ligand architecture to enable aerobic C-H oxidation at a platinum center

254th National Meeting (2017)

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