The dicationic complexes [(ArN=C(Me)-C(Me)=NAr)Pt(Solv)(2)]X-2, (Ar = 2,6-(CH3)(2)C6H3; 5a: solv = CH3CN, X = CF3SO3-, BF4-, SbF6-; 5b: solv = (CH3)(2)CO, X = BF4-, SbF6-) and (CyN=C(H)-C(H)=NCy)Pt(CH3CN)(2)]X-2, (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 sp(2) C-H bond of the unsaturated sidegroup. Pyridines with saturated groups at the 2-position do not undergo a similar cyclometalation reaction. In trifluoroethanol-d(3) solution, 6 undergoes cyclometalation of one of the cyclohexyl groups, an example of sp(3) 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. (C) 2002 Elsevier Science B.V. All rights reserved.