CH bond activation

Scheme 10.6 CH bond activation within a tetrahedral self-assembled cluster.24...

Stone KL, Borovik AS. Lessons from nature unraveling biological CH bond activation. Curr Opin Chem Biol. 2009 13 114-8. 

Koga N, Morokuma K. SiH, SiSi, and CH bond activation by coordinatively unsaturated RhCl(PH3)2. Ab initio molecular orbital study. J Am Chem Soc 1993 115(15) 6883—6892. 

The activation of sp2- or sp-hybridized CH bonds (for reviews on metal-mediated CH bond activation in catalytic processes see [132-137]) generating an organopalladium species suitable for subsequent transformation is the key step for sequences initiated by CH activation. 

CH-bond Activation Using Germylenes. The discussion of CH-activation using germylenes was presented in Section 3.1.6. 

Marks has reviewed this area. Basset has bound organometallic species to a silica surface and seen interesting alkane reactions that go via initial CH bond activation this step probably proceeds by a sigma bond metathesis pathway since the metals involved are d . Snbseqnent reactions inclnde CC bond cleavage and carbon skeletal rearrangements. 

For activated CH bonds a wealth of chemical methods is available, such as singlet oxygen, A-bromosuccinimide, Br2/hv, Pb(OAc)4, or SeOi [58]. Anodically fair yields are obtained for CH bonds activated by a vinyl, phenyl, or alkoxy group, although sometimes... 

Different from methane, it already will strongly interact in the predissodation adsorbed state. This is due to the availability for adsorption through the free valence of NH3. For methane, the molecule has to distort substantially so that close contact between C and H atom becomes possible and CH bond activation can occur. This is different for NH3. Through its lone-pair orbital, it is initially adsorbed atop of a metal atom. While NH2 prefers adsorption in twofold coordination, upon dissociation... 

We observe the initial bond order of the CH bond that is cleaved to be close to one. It decreases to 0.29 in the transition state. This implies a more substantial weakening in contrast to the assumption of the activation strain model. The M-H and M-C bond orders are, respectively, 0.38 and 0.43, to be compared with the final state values 0.42 and 0.54, respectively. Compared to the initial CH bond interaction in the transition state, the CH bond interaction has been substantially weakened. One also finds that the M-C and M-H interactions are already close to those of the final state. The bonding interactions are distributed in a close to even distribution over the three bonds of H-C, C-Rh, and H-Rh. In the final state, the dissociating H atom moves to a twofold adsorption site. The closeness of the bondorders of the C-Rh bond and one of H-Rh bonds to those in the final state illustrates the late transition state nature of CH bond activation. 

Scheme 6.14 Arene CH bond activation by (PSiP)lr complexes.

The attempted alkylation of 56 with MeLi in benzene solution resulted in quantitative formation of the phenyl hydride complex 58 with concomitant evolution of methane (Scheme 6.14) [39]. The targeted methyl hydride complex 57 can be observed in situ and rapidly reacts to generate 58 via CH bond activation of the benzene solvent Complex 58 also undergoes facile arene exchange, as indicated by the formation of tolyl hydride species (59) upon treatment of 58... 

This review will deal with the direct and indirect anodic oxidation of unactivated CH bonds in alkanes, and of remote CH bonds in substrates with various functional groups. The conversion of CH bonds activated by vinyl, aryl, amino or alkoxy groups will not be dealt with in this chapter. However, the catalytic oxidation of alkanes in fuel cells and the oxidation of alkanes with molecular oxygen and iron catalysts are included. 

Polyhydrido complexes are often utilized for the CH bond activation, for example, ReH7(PCy3)2/ During heating of this complex in (333-353 K) reductive... 

A variety of low valent aryloxide derivatives of the early transition metals undergo intramolecular CH bond activation. Attempts to isolate the d -species [M(OAr)3] or [M(OAr)2Cl] (OAr = 2,6-di-rcrt-butylphenoxide or 2,6-di-phenylphenoxide M = Nb, Ta) by reduction of the corresponding d -chloride leads instead to bis-cyclometallated compounds (Eq. 6.60). ... 

Recent studies have focussed on the generation of metaUation-resistant aryloxide ligation. The strategy adopted has involved the introduction of meto-substituents onto the 2,6-diphenylphenoxide nucleus. The meta-substituents restrict rotation of the orthophenyl ring into a position for CH-bond activation. In the case of 3,5-di-tert-butyl-2,6-diphenylphenoxide, cyclometallation by tantalum alkylidene functional groups is... 

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