title: Competitive activation of C-H and C-X bonds in reactions of Pt+ with CH3X (X=F,Cl): experiment and theory.
abstract: The reactions of Pt(+) with CH(3)X (X=F, Cl) are studied experimentally by employing an inductively coupled plasma/selected-ion flow tube tandem mass spectrometer and theoretically by density functional theory. Dehydrogenation and HX elimination are found to be the primary reaction channels in the remarkably different ratios of 95:5 and 60:40 in the fast reactions of Pt(+) with CH(3)F and CH(3)Cl, respectively. The observed kinetics are consistent with quantum chemistry calculations, which indicate that both channels in the reaction with CH(3)F are exothermic with ground-state Pt(+)((2)D), but that HF elimination is prohibited kinetically because of a transition state that lies above the reactant entrance. The observed HF-elimination channel is attributed to a slow reaction of CH(3)F with excited-state Pt(+)((4)F) for which calculations predict a small barrier. The calculations also show that both the HCl-elimination and dehydrogenation channels observed with CH(3)Cl are thermodynamically and kinetically allowed, although the state-specific product distributions could not be ascertained experimentally. Further CH(3)F addition is observed with the primary products to produce PtCH(2) (+)(CH(3)F)(1,2) and PtCHF(+)(CH(3)F)(1,2). With CH(3)Cl, sequential HCl elimination is observed with PtCH(2) (+) to form PtC(n)H(2) (n) (+) with n=2, 3, which then add CH(3)Cl sequentially to form PtC(2)H(4) (+)(CH(3)Cl)(1-3) and PtC(3)H(6) (+)(CH(3)Cl)(1,2). Also, sequential addition is observed for PtCHCl(+) to form PtCHCl(+)(CH(3)Cl)(1,2).
authors.affiliation: Centre for Research in Mass Spectrometry and Centre for Research in Earth and Space Science, Department of Chemistry, York University, Toronto, ON M3J 1P3, Canada.
authors.forename: Xiang
authors.initials: X
authors.lastname: Zhao
authors.forename: Alan C
authors.initials: AC
authors.lastname: Hopkinson
authors.forename: Diethard K
authors.initials: DK
authors.lastname: Bohme