Intramolecular CH activation by dicationic Pt(II) complexes

The dicationic complexes [(ArNC(Me)C(Me)NAr)Pt(solv)2]X2, (Ar=2,6-(CH3)2C6H3; 5a: solv=CH3CN, X=CF3SO3−, BF4−, SbF6−; 5b: solv=(CH3)2CO, X=BF4−, SbF6−) and [(CyNC(H)C(H)NCy)Pt(CH3CN)2]X2, (Cy=C6H11, 6: X=OTf−, BF4−, PF6−, SbF6−) were synthesized from the corresponding Pt dichlorides with two equivalents of AgX. The reactions of 5a with 1-phenylpyrazole, 2-phenylpyridine, 2-vinylpyridine, and 2-(2-thienyl)pyridine afford the cyclometalated products 11–14 via intramolecular CH activation of an sp2 CH bond of the unsaturated sidegroup. Pyridines with saturated groups at the 2-position do not undergo a similar cyclometalation reaction. In trifluoroethanol-d3 solution, 6 undergoes cyclometalation of one of the cyclohexyl groups, an example of sp3 CH bond activation. The latter reaction proceeds only partway to completion, implying that an equilibrium has been reached; in the case where X=OTf−the equilibrium favors the starting dication.