Methane coordination theoretical calculations

In a study of the methane complex [(diimine)Pt(CH3)(CH4)]+ (diimine = HN=C(H)-C(H)=NH), relevant to the diimine system experimentally investigated by Tilset et al. (28), theoretical calculations indicate preference for the oxidative addition pathway (30). When one water molecule was included in these calculations, the preference for oxidative addition increased due to the stabilization of Pt(IV) by coordinated water (30). The same preference for oxidative addition was previously calculated for the ethylenediamine (en) system [(en)Pt(CH3)(CH4)]+ (151). This model is relevant for the experimentally investigated tmeda system [(tmeda)Pt(CH3)(solv)]+ discussed above (Scheme 7, B) (27,152). For the bis-formate complex Pt(02CH)2, a a-bond metathesis was assumed and the energies of intermediates and transition states were calculated... 

Over the past 15 years, many theoretical treatments of C-H activation have appeared. Early work by Hoffmann addressed qualitative orbital approaches to C-H activation by CpML fragments [52]. More quantitative approaches have appeared recently for the addition of methane to the [CpRh(CO)] fragment [53— 56]. These more recent calculations provide support for the presence of methane a-complexes along the reaction coordinate for methane oxidative addition, and confirm the weak nature of the interaction between the metal center and the C-H sigma bond ( 20 kj mol-1). A more detailed comparison of these results is beyond the scope of this chapter. 

Varied Methane Cations The methane molecular ion (methane radical cation, CI b -), the parent ion in MS, and the methane dication (CH42 ) are of great significance and have been the subject of experimental and theoretical studies. Its five-coordinate planar structure was suggested in the early calculations by Olah and Klopman, and indeed shown to be correct in subsequent more advanced studies. 

---