Metal−Alkyl Bond Protonolysis Studies of (dfepe)Pt(Me)X Complexes in Acidic Media

Protonolyses of (dfepe)Pt(Me)X (dfepe = (C 2 F 5 ) 2 PCH 2 CH 2 P(C 2 F 5 ) 2; X = O 2 CCF 3, OSO 2 H, OSO 2 CF 3, OSO 2 F) complexes in their respective neat acid solutions cleanly yield (dfepe)Pt(X) 2 products with rates dependent on relative acid strengths. No (dfepe)Pt(Me)(X) 2 (H) + intermediates were observed by variable-temperature NMR in dichloromethane. The (perfluoroaryl)phosphine analogue (dfppe)Pt(Me) 2 (dfppe = (C 6 F 5 ) 2 PCH 2 CH 2 P(C 6 F 5 ) 2 ) is much less resistant to protonolysis and rapidly converts to (dfppe)Pt(OTf) 2 in HOTf at 20 °C. Kinetic studies for protonolysis in CF 3 CO 2 H(D) and CF 3 SO 3 H(D) solvents were carried out. Examination of ionic strength and chloride anion effects in trifluoroacetic acid indicate that prior association of anion to (dfepe)Pt(Me)X systems is not kinetically important. k H / k D values were obtained from competitive protonolysis studies (CF 3 CO 2 H, 9 ± 2 (20 °C); H 2 SO 4, 7 ± 2 (100 °C); CF 3 SO 3 H, 2.7 ± 0.7 (100 °C)). In the case of CF 3 CO 2 H, separate kinetic runs in protio and deuterio acids gave a lower k H / k D value of 3.6(4). The data obtained in these studies do not differentiate between limiting S E 2 and S E (oxidative) protonolysis mechanisms.