Alkane activation stoichiometric chemistry

Synthetic organic chemistry applications employing alkane C-H functionalizations are now well established. For example, alkanes can be oxidized to alkyl halides and alcohols by the Shilov system employing electrophilic platinum salts. Much of the Pt(ll)/Pt(rv) alkane activation chemistry discussed earlier has been based on Shilov chemistry. The mechanism has been investigated and is thought to involve the formation of a platinum(ll) alkyl complex, possibly via a (T-complex. The Pt(ll) complex is oxidized to Pt(iv) by electron transfer, and nucleophilic attack on the Pt(iv) intermediate yields the alkyl chloride or alcohol as well as regenerates the Pt(n) catalyst. This process is catalytic in Pt(ll), although a stoichiometric Pt(rv) oxidant is often required (Scheme 6).27,27l 2711... 

Currently, one of the most sought after procedures in organometallic chemistry is a homogeneous catalytic cycle that involves the activation of a C-H bond in an alkane. We have just examined the oxidative addition of C-X bonds, and in Section 12.3 we will show how this activation of the C-X bond leads to further chemistry. Regardless of how useful this may be, one still needs a C-X bond to start. It would be very useful to directly activate a C-H bond in an alkane, without needing to first create a C-X bond. However, the oxidative addition of a standard C-H bond is a rare reaction. A handful of systems have been developed, and we discuss two. No homogeneous catalytic cycles have yet to be developed, so the examples are simply stoichiometric reactions. 

It is now extremely frequent in transition-metal chemistry in which it plays a key role in catalytic processes. Usually, it involves organic halides and substrates of the RH type (R = H, CN, SiMes), these categories of substrates being frequently involved in catalysis. Other substrates whose activation would be very valuable such as alkanes sometimes undergo stoichiometric oxidative addition, most often with late, third-row transition metals. The mechanism varies and depends on the polarity of the A-B bond and the nature of the complex. We will distinguish the classic 3-center concerted mechanism, the bimolecular nueleophihe substitution, the ionic mechanism and the radical-type mechanisms. 

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