Dewar-Chatt-Duncanson model for

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

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

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

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). 

The two extremes of the Dewar-Chatt-Duncanson model for olefin coordination can also be applied to describe aldehyde, ketone, and imine complexes. Resonance structure A is an rf complex of Zr(II), while its resonance structure B is a zirconaaziridine containing Zr-C and Zr-N bonds (Fig. 6). X-ray structural studies of zirconaaziridines and their observed reactivity suggest that resonance structure B is more important. 

The classical Dewar-Chatt-Duncanson model for metal-alkene bonding has been revisited with a combination of X-ray structural data (see Diffraction Methods in Inorganic Chemistry) and DFT calculations (see Molecular Orbital Theory), particularly on complexes of the type (acac)Rh(alkene)2. These indicate the existence of distortions from idealized geometry involving a twist (127), where the axis of the double bond is no longer perpendicular to the molecular plane and a roll (128), where the line... 

Schwartz s reasoning for optimizing these thermodynamic considerations led to the development of hydrozirconation. Hydride complexes of the late transition metals do not in general exhibit the hydrometallation reaction, probably because the alkene complexes are too stable. This may be understood from the Dewar-Chatt-Duncanson model for alkene bonding, wherein back donation of metal d-elec-trons to the alkene Tr -orbital is a major contributor. For metal centers with d -electron configurations, there should be substantial stabilization of (3) with respect to (2). Such metals are only found towards the left end of the Periodic Table, particularly Groups III A to VA. 

The metal-dihydrogen bonding is similar to the Dewar-Chatt-Duncanson model for metal-olefin bonding [29-31]. There is a donor bond from the electron pair in the bonding orbital of the H2 ligand into an empty metal orbital (Figure 1, left-hand side). 

G.J. Kubas, Metal-dihydrogen and sigma-bond coordination the consummate extension of the Dewar-Chatt-Duncanson model for metal-olefin pi bonding . Journal of Organometallic Chemistry, 635, 37 (2001). 

The current understanding of the nature of the metal-( 72-H-X) bonding interaction for various types of cr-complexes is based on the traditional Dewar-Chatt-Duncanson model for the well-known 7r-olefin complexes which emphasizes both ligand-to-metal a bonding and metal(d7r)-to-ligand(a )... 

Remarkably, one of the simplest conceivable H2 complexes, [Ru(H20)s(H2)]2+, can be formed by displacement of an aquo ligand from the hexaquo complex by pressurized H2.14 It seems astonishing that interaction of a bonding electron pair could be on a par with that for a lone pair. What is unique about the three-center bonding in M-H2 and other bond complexes that stabilizes them and sets them apart from species such as carbocations is BD, i.e., donation of electrons from a filled metal d orbital to the a orbital of the H-H bond, similar to metal donation to n orbitals in the Dewar-Chatt-Duncanson model for olefin coordination. 

Figure 4.2. Comparison of M-H2 coordination to Dewar-Chatt-Duncanson model for M-L n bonding.

This bonding scheme is completely analogous to the Dewar-Chatt-Duncanson model for the interaction of an ethylene molecule with a metallic centre (Chapter 3, 3.4), the ncc and jr, MO being replaced here by the ohi and MO. 

Figure 24 The Dewar-Chatt-Duncanson model" for coordination of an olefin in which donation of electron density from the filled olefin rr-orbital (an L function) is supplemented by backbonding into the empty 7r -orbital (aZfunction). Depending upon the extent of backbonding, the compound may be described as either a metal-olefin adduct (little backbonding) or a...

Salvi N, Belpassi L, Tarantelli F (2010) On the Dewar-Chatt-Duncanson model for catalytie gold(I) eomplexes. Chem-Eur J 16(24) 7231-7240. doi 10.1002/chem.201000608... 

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