Dewar-Chatt bonding model

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.

Fig. 3. Schematic bonding pictures for transition metal atoms (M) binding to C2H4 via the Dewar-Chatt-Duncanson model.

The bonding between these two fragments can be understood using the Dewar-Chatt-Duncanson model of donation and backdonation [79, 80], The frontier orbitals responsible for these interactions between 15 and 16-R are drawn to scale in Figure 15. 

In accord with the Dewar-Chatt-Duncanson model, we find that the dominant interaction is donation from the C C n bond into the rhodium LUMO. This interaction is enhanced when the double bond lies in the rhodium-diphosphine plane and with electron donating substituents which raise the energy of 7ito more closey match the LUMO Charge Decomposition Analysis (CDA) [81] shows that the amount of donation is... 

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 electronic structure of the surface chemical bond is discussed in depth in the present chapter for a number of example systems taken from the five categories of bonding types (i) atomic radical, (ii) diatomics with unsaturated -systems (Blyholder model), (iii) unsaturated hydrocarbons (Dewar-Chatt-Duncanson model), (iv) lone pair interactions, and (v) saturated hydrocarbons (physisorption). 

Fig. 2. The Dewar-Chatt-Duncanson model for olefin bonding showing the

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). 

Figure 7. The metal r 2-silane bonding interactions based on the Dewar-Chatt-Duncanson model.

The bonding of transition metal fragments to a silicon surface can also be described with the Dewar-Chatt-Duncanson model. There is a striking similarity between the reactivity of the Si(100) surface and that of disilene (Si2H4)97. 

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... 

G. J. Kubas, Metal-Dihydrogen and cr-Bond Coordination The Consummate Extension of the Dewar-Chatt-Duncanson Model for Metal-Olefin n Bonding, J. Organomet. Chem. 635, 37-68 (2001). 

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