Methane transition metal halides

The observation that the metal carbene complex, (CO)5W = C(Ph)2 [22], catalyzed the polymerization of cyclic olefins to ring opened polymers containing the diphenylmethylene unit of the catalyst provided additional evidence that carbenes were involved in the catalytic cycle. The formation of the initiating metal carbenes in the classic systems that consist of transition metal halides and alkylating agents was proposed to involve metal alkylation followed by oc-hydrogen loss, Eq. (6). Methane and propene were detected in the early stages of these reactions [23]. 

This mechanism is quite general for this substitution reaction in transition metal hydride-carbonyl complexes [52]. It is also known for intramolecular oxidative addition of a C-H bond [53], heterobimetallic elimination of methane [54], insertion of olefins [55], silylenes [56], and CO [57] into M-H bonds, extmsion of CO from metal-formyl complexes [11] and coenzyme B12- dependent rearrangements [58]. Likewise, the reduction of alkyl halides by metal hydrides often proceeds according to the ATC mechanism with both H-atom and halogen-atom transfer in the propagation steps [4, 53]. 

Siegbahn PEM, Blomberg MRA (1994) Halide ligand effects on the oxidative addition reaction of methane and hydrogen to second row transition metal complexes. Organometallics 13 354... 

The ALMO-EDA scheme was used to analyze a wide range of methane CH bond cleavage transition states for metal-ligand complexes that have been reported experimentally to promote or catalyze CH activation [57]. This included late transition metals such as Rh(lll), Rh(l), lr(ni), Pt(n), Pd(ll), Ru(II), and Au(III) and early transition metals such as Sc(lll) and W(ll). Ligands attached to these metal centers range from phosphine, N-heterocycle, and halide to 0-donors. Three specific examples of transition states analyzed and their ALMO-EDA interaction energy components are shown in Scheme 10. 

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