Dewar-Chatt-Duncanson complex

Features (2) and (3) are explicable in terms of the Dewar-Chatt-Duncanson model for bonding in alkene complexes (Figure 3.63), which involves... 

Surprisingly, in contrast to the reaction of the Si=P bond with mesityl azide, the reaction of 15a with diphenyldiazomethane resulted in the formation of the [2+l]-cycloadduct 35 (Scheme S).38 The bonding situation in 35 (Fig. 11) may be described in terms of a 7r-complex, by employing the Dewar-Chatt-Duncanson model, in which the Si=P bond acts as v donor and acceptor at the same time (Scheme 9). The corresponding [2+31-cycloaddition product 36 was generated only on thermal activation of 35. 

Scheme 9. Description of 35 as 77-complex (Dewar-Chatt-Duncanson model) (a) Si=P bond as ir-donor (b) Si=P bond as 77-acceptor.

The Dewar-Chatt-Duncanson model of the binding of an olefin in a transition metal complex involves two types of interactions. Transfer of electron density from the relatively high-lying olefinic ic-orbital to the metal (cf. 20) represents a Lewis acid Lewis base interaction (a-bonding). A metal-olefin jr-bond due to interaction... 

The course of modern organometallic chemistry has been greatly influenced by three simple generalizations the Dewar-Chatt-Duncanson synergic bonding model for metal-olefin complexes (40, 72) Pauling s electroneutrality principle (174), and the 18-electron or inert gas rule (202). In this section the impact of recent theoretical calculations on these important generalizations will be evaluated. 

Chemical and physical properties of metal alkene complexes have been rationalized on the basis of the Dewar-Chatt-Duncanson bonding model167,1 8 and a number of semiempirical and ab initio MO calculations have been performed for a more quantitative description of the bonding.16 "177... 

Figure 3.55 Dewar Chatt Duncanson bonding model in metal alkene complexes.

Positively-charged fragments such as [ML,]+, CH , and H + are all strong electrophiles ( superelectrophiles in the extreme sense (13)) towards the Lewis basic H2, but transition metals can uniquely stabilize H2 and other cr-bond coordination by back donation from d-orbitals that main group analogues cannot do. This bonding is then remarkably analogous (14) to the Dewar-Chatt- Duncanson model (15) for ji-complexes (6). 

Fig. Dewar-Chatt-Duncanson model for bonding in p complexes of C2H4. 

The Dewar-Chatt-Duncanson model of bonding in ethene complexes is shown in figure below. And is analogous to the... 

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