Synergic Bonding Models

The d electrons in heavy metals, bromine, etc. have the correct symmetry to interact with the antibonding jt-molecular of an olefin, in x-complexes from the olefin and the heavy atom. If the latter carries d-electrons, it can therefore form a second dative molecular bond with the vacant antibonding x-molecular orbital, opposite in direction to the normal molecular bond. This is illustrated diagrammatically below, the phases of the lobes of the 

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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. 

Fig. 20 Synergic bonding model for x-acceptor ligands such as CO, NO and CN...

A covalent bonding model is needed to account for the effects of Jt-donor or 7i-acceptor ligands and synergic bonding. A molecular orbital description provides a more universal description of bonding within transtion metal complexes. 

Such shifts can be rationalized in terms of the model of synergic a and ir bonding of the CO ligand in metal carbonyls (29) as was proposed by Blyholder (30). The formation of a strong surface bond involves considerable back donation from metal d... 

The cluster valence electron (c.v.e.) count usually corresponds to 12 + 22 electrons. Bonding of the C2 unit involves stabilization of a, a, and ji orbitals by interaction with radial metal MOs of the same symmetry, together with overlap of ji orbitals with filled metal MOs, i.e., a similar synergic interaction to the familiar bonding mode found in alkyne-metal complexes. For the model [Co8(C2)(n-L)(L)8]4 based on two trigonal... 

The i.r. absorption intensities of the v(N 4) stretching mode in a series of rhenium(i) dinitrogen complexes have been determined and the intensity found to increase with decreasing frequency in agreement with the synergic model of Re—N=N bonding (cf. Vol. 2, p. 132). Acylazo-rhenium(iii) complexes,... 

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