Bonding synergic

Electron-impact ionization potentials have been determined for [W(CO)sL] (L = 2,6-Mepy, 4-Mepy, or 2-CNpy) and for the free ligands. A good linear correlation was obtained between the two values in this and other series of compounds and the results were rationalized in terms of a synergic bonding mechanism. ... 

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. 

Figure 3.54 Synergic bonding in CO (a) donation of electron density from ligand to unoccupied metal p- or s-orbital and (b) metal-to-Ligand backbonding.

Transition-metal-olefin 7r-complexes exhibit synergic bonding, which involves interaction of the filled olefin 7r-orbitals with empty metal d orbitals, and backbonding from the filled metal d orbitals to the empty 7r olefin orbitals. The net result is that stable metal-olefin 7r-complexes are formed when the metal is electron-rich (low oxidation state) and the olefin is electron deficient (32). The opposite situation would occur in 7r-complex 24 and the bonding mode may be different since the metal is in a high oxidation state. This suggested to us that olefin 7r-complexes of trivalent cobalt might be stablized by an electron-rich olefin. 

Figure 1.12 Synergic bonding of CO to a transition metal implications for nucleophilic (Nu ) attack...

Figure 2.22 Synergic bonding in dihydrogen coordination hydrogen to metal donation and metal to hydrogen retrodonation...

Figure 5.34 Carbyne [CR]+ frontier orbitals for synergic bonding with transition metals...

A key feature of alkene coordination is the loss of planar symmetry. Indeed, it is this loss of symmetry that allows the vc=c IR absorption of alkene complexes to be observed (IR inactive for the free molecule). Consistent with the synergic bonding description, coordination leads to a decrease in the C=C bond strength and accordingly a decrease in the value of vc=c. The case of prochiral alkenes is of particular importance,... 

Figure 1 Diagrammatic representation of the synergic bonding in a metal carbonyl forward a-donation from a filled CO orbital, balanced by back-donation from metal orbitals of appropriate symmetry into the CO n orbitals.

The synergic bonding in the metal-olefin complexes also reduces the bond order of the coordinated C-C bond, but these changes are less easily detected than those in the metal carbonyls. 

P-donor ligands usually form phosphorus-metal bonds with a main group or transition metal that are essentially covalent and in which the phosphorus is the lone pair donor. Despite the vast number of complexes prepared, often with elaborate architecture, the nature of the phosphorus-metal bond remains elusive and controversial, in particular, for transition metals. The simple statement of the bond as a neutral donor-acceptor complex has been elaborated by identifying the many contributing factors. We will discuss the steric factor and the electronic component of the P-M bond separately. The separation of the electronic component into a and n factors is a formal exercise, the reality being Synergic Bonding, wherein these electronic factors are mutually dependent. 

Figure 6.18 Examples of synergic bonding interactions (a) in carbonyl complexes (b) in alkene complexes...

Bond distances obtained by single-crystal X-ray diffraction structural studies can provide another source of information about synergic bonding in transition metal complexes. However, such data need to be used with care, since changes in bond lengths are small and may be less than the experimental errors in determining the bond distances. 

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. 

Stable complexes 78 Stability constant 75 Steric effects 84 Superconductors 13 Symmetry labels 100 Synergic bonding 120, 122... 

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