Infrared Spectra of Platinum Insertion and Methylidene Complexes Prepared in Oxidative C-H(X) Reactions of Laser-Ablated Pt Atoms with Methane, Ethane, and Halomethanes

Reactions of laser-ablated Pt atoms with CH4 and C2H6 produce CH3-PtH and CH3CH2-PtH via oxidative C-H insertion and show that the Pt atom is an effective C-H insertion agent. The methylidene CH2=PtH2 is also detected in methane experiments. Methyl fluoride, CH3F, on the other hand, yields C-H as well as C-F insertion products (CH2F-PtH and CH3-PtF). The CH3-PtF molecule exists in photochemical equilibrium with an agostic CH2(H)-PtF isomer in the matrix, which is unique for an insertion product, and the CH2=PtHF methylidene appears to participate in the rearrangement process. Moreover, CHF=PtHCl, CHF=PtHF, and CF2=PtHF are primary products from the reactions of CH2FCl, CH2F2, and CHF3, while CHCI=PtCl2 is generated from CHCl3. The surprising preference of the Pt-H over the Pt-F bond in reactions of fluorine containing precursors is traced to the similar Pt-H and Pt-F bond energies. The formation of small Pt carbenes also reveals that high oxidation-state complexes are favored in reactions with di- and trihalomethanes as well as in previously studied reactions of Pt and tetrahalomethanes. Calculations show that endothermic HF elimination from CHF=PtHF can produce the HC Ptf molecule, which contains a platinum-carbon triple bond.