Ligand Effects on the Mechanisms of Thermal Bond Activation in the Gas-Phase Reactions NiX+/CH4→Ni(CH3)+/HX (X=H, CH3, OH, F). Short Communication

✍ Scribed by Maria Schlangen; Helmut Schwarz

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: German
• Weight: 472 KB
• Volume: 91
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200890238

✦ Synopsis

The thermal ion-molecule reactions NiX þ þ CH 4 ! Ni(CH 3 ) þ þ HX (X ¼ H, CH 3 , OH, F) have been studied by mass spectrometric methods, and the experimental data are complemented by density functional theory (DFT)-based computations. With regard to mechanistic aspects, a rather coherent picture emerges such that, for none of the systems studied, oxidative addition/reductive elimination pathways are involved. Rather, the energetically most favored variant corresponds to a s-complexassisted metathesis (s-CAM). For X ¼ H and CH 3 , the ligand exchange follows a two-state reactivity (TSR) scenario such that, in the course of the thermal reaction, a twofold spin inversion, i.e., triplet ! singlet ! triplet, is involved. This TSR feature bypasses the energetically high-lying transition state of the adiabatic ground-state triplet surface. In contrast, for X ¼ F, the exothermic ligand exchange proceeds adiabatically on the triplet ground state, and some arguments are proposed to account for the different behavior

does not undergo a thermal ligand switch, the DFT computations suggest a potential-energy surface that is mechanistically comparable to the NiF þ /CH 4 system. Obviously, the ligands X act as a mechanistic distributor to switch between single vs. two-state reactivity patterns.