The (2,6-dimethylbenzenethiolato)platinum(II) complexes PtR(SC6H3Me2-2,6-κ1 S)L2 (R = Me, L = PMe3 (1a), PPh3 (1c), L2 = dppe (1d), dppp (1e); R = Et, L = PPh3 (2c); R = CH2CMe3, L = PPh3 (3c)) and Pt(SC6H3Me2-2,6-κ1 S)2L2 (L = PMe3 (4a), PEt3 (4b), PPh3 (4c), L2 = dppe (4d), dppp (4e), dppb (4f)) have been prepared. Heating of these compounds results in an internal sp3 C–H bond cleavage reaction, giving the thiaplatinacycle complexes Pt[SC6H3(CH2-2)(Me-6)-κ2 S,C]L2 (L = PMe3 (5a), PEt3 (5b), PPh3 (5c), L2 = dppe (5d), dppp (5e), dppb (5f)) in moderate to quantitative yields. The reactions of 1c and 4c proceed via prior dissociation of PPh3, and a concerted mechanism is proposed. Of particular interest is the sp3 C–H bond activation step, whose observed rate constant for 4c is no less than 104-fold faster than that for 1c. The arenethiolato group is expected to enhance the C–H bond cleavage step as a hydrogen acceptor.