The cyclometalated platinum(II) complexes [PtMe-(C<^>N)(L)] [1(PS): C<^>N = 2-phenylpyridinate (ppy), L = SMe2; 1(BS): C<^>N = benzo[h]quinolate (bhq), L = SMe2; 1(PP): C<^>N = ppy, L = PPh3; and 1(BP): C<^>N = bhq, L = PPh3] containing two different cyclometalated ligands and two different ancillary ligands have been investigated in the reaction with CX3CO2H (X = F or H). When L = SMe2, the Pt-Me bond rather than the Pt-C bond of the cycloplatinated complex is cleaved to give the complexes [Pt(C<^>N)(CX3CO2)(SMe2)]. When L = PPh3, the selectivity of the reaction is reversed. In the reaction of [PtMe(C<^>N)(PPh3)] with CF(3)CO2(H), the Pt-C<^>N bond is cleaved rather than the PtMe bond. The latter reaction gave [PtMe(kappa N-1-Hppy)(PPh3)(CF3CO2)] as an equilibrium mixture of two isomers. For L = PPh3, no reaction was observed with CH3CO2H. The reasons for this difference in selectivity for complexes 1 are computationally discussed based on the energy barrier needed for the protonolysis of the Pt-C-sp(3) bond versus the Pt-C-sp(2) bond. Two pathways including the direct one-step acid attack at the Pt-C bond (S(E)2) and stepwise oxidative-addition on the Pt(II) center followed by reductive elimination [S-E(ox)] are proposed. A detailed density functional theory (DFT) study of these protonations along with experimental UV-vis kinetics suggests that a one-step electrophilic attack (S(E)2) at the Pt-C bond is the most likely mechanism for complexes 1, and changing the nature of the ancillary ligand can influence the selectivity in the Pt-C bond cleavage. The effect of the nature of the acid and cyclometalated ligand (C<^>N) is also discussed.