| B3LYP calculations have been performed to investigate various aspects of alkyl-hydride reductive elimination reactions from platinum complexes. It was determined, from calculations on (PH3)2Pt(CH 3)H and Cl2(PH3)2Pt(CH3)H model complexes, that reduced phosphine binding enthalpy in the Pt(IV) complex is the primary reason that a ligand predissociation mechanism is preferred, whereas a direct mechanism is preferred by Pt(II). In fact, forced methane elimination from several stereoisomers of Cl2(PH3) 2Pt(CH3)H caused concomitant ligand dissociation. Therefore, the ΔH‡ for direct C-H reductive elimination from Cl2(PH3)2Pt(CH3)H was estimated. Comparison of these results with those of calculations on analogous complexes, in which the PH3 ligands were replaced with PMe 3 ligands, shows that the ligand-predissociation mechanism was selectively disfavored by increasing the basicity of the phosphine ligands. As a result, it was possible to find the transition structure for direct C-H reductive elimination from several stereoisomers of Cl2(PMe3) 2Pt(CH3)H, in contrast to the results found for the PH 3-ligated complexes.; In addition, multireference CASSCF and CASPT2 calculations were performed on perfluorocyclobutyne. In contrast to the results of single reference methods, CASPT2(12,12)/cc-pVTZ calculations predict that perfluorocyclobutyne exists in a shallow potential minimum, with a barrier to isomerization of Δ H‡ = 2.3 kcal/mol. The isomerization reaction is virtually thermoneutral, ΔHrxn = −0.7 kcal/mol. The product cyclopropylidene carbene is found computationally to adopt a very bent, Cs geometry. UB3LYP/6–31+G* calculations were performed on the radical anion of perfluorocyclobutyne, and found that the most likely isomerization occurs with a reasonably high barrier of Δ H‡ = 19.5 kcal/mol. The NI-PES of the radical anion was simulated by calculation of the Franck-Condon factors for several transitions, and the qualitative features of the spectrum are predicted. Finally, the syntheses of two possible precursors of the radical anion of perfluorocyclobutyne are described: 3,3,4,4-tetrafluorocyclobutene, and 1,2-bis-trimethylsilyl-3,3,4,4-tetrafluorocyclobutene. |
