Bonding Chatt-Dewar-Duncanson model

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

The Dewar-Chatt-Duncanson Bonding Model of Transition Metal-Olefin Complexes... 

Figure 4.1 Schematic representation of various types of covalent bonding, (a) Electronsharing bonding, (b) Donor-acceptor bonding, (c) Dewar-Chatt-Duncanson bonding model for transition metal complexes.

E. Gullo, G. S. McGrady, P. Sirsch. Valence shell charge concentrations and the Dewar-Chatt-Duncanson bonding model. 

The Dewar-Chatt-Duncanson (DCD) model describes the formation of two coordinate bonds resulting from the overlap of two metal and two ligand orbitals. In other words, the DCD model of bonding of organometallic complexes is nothing else but a simple model of metal-ligand double multicenter bonding. Now, since two multicenter bonds can be formed in three distinct ways, i.e., they can be U,... 

Low-Temperature Ethylene Adsorption on Ni(lll) The adsorption of ethylene on metal surfaces can be understood in terms of the Dewar-Chatt-Duncanson (DCD) model [73], put forward to rationalize ethylene coordination in organometaUic clusters. Essentially, the interaction is controlled by donation of electron density from the highest occupied molecular tt level and backdonation from the metal into the empty tt level. Both types of electron transfers increase the metal-molecule bond strength and decrease the molecular carbon-carbon bond. On the basis of this model, three extreme descriptions of adsorbed ethylene can be formulated, depicted as the di-a, the metallocyclopropane, and the tt-adsorbed species [67, 74], Figure 3.4.1.8a. The vibrational fingerprints for these species have been reviewed [22, 23, 52, 67] and fall within three main patterns. Figure 3.4.1.8b... 

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 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. 

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