Number of Electrons Donated to the Metal

A methyl group is considered to donate two electrons and to be an anionic, two-electron ligand by the first classification system and is considered to donate one electron and to be an X-type ligand by tine second classification system. 

Ligand Formal charge Ionic model Covalent model Bonding mode 

alkynyl, silyl, germyl, stannyl, alkoxo, amido, thiolato, or phosphide -1 2 1  

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The synthesis and characterization of a family of mono-Gp dichloro complexes with disubstituted aryloxo ligands has been reported, and their molecular structures provide some means of quantifying the number of electrons donated to the metal center by an aryloxide ligand. These complexes can be reduced by Grignard reagents or LiBu11 in the presence of enynes. The formation of metallacyclic derivatives (Scheme 348) was observed for the Cp but not for the Cp complexes, as deduced by NMR spectroscopy. The complexes have been investigated as catalysts... 

Table 1.1 summarizes the structures, the formal charges assigned by the first classification system, and the number of electrons donated to the metal center for a series of common ligands. In most cases, ligands coordinated through a single electron pair on a single... 

Polyenes are also considered as Lewis bases. They are counted such that all their bonding and nonbonding levels are occupied. Some representative examples are given in 16.10. Listed below each structure is the number of electrons donated to the metal. Some care, however, must be used to establish the connectivity of these... 

In addition to carbenes exerting a strong trans influence (thermodynamic), which may be manifest as a trans effect (kinetic) in ligand substitution reactions, heteroatom-functionalized carbene ligands (with their associated dipolar resonance contributor, Figure 1.16) may assist in the stabilization of transition states of reduced coordination number by electron donation to the metal. 

The fact that in the formation of the MC bond in carbonyls the metal always donates an even number of electrons, and that in the nitrosyls the number of electrons donated by the metal to the MN bond is always odd, is the reason for the formation of mono-metallic carbonyl-nitrosyl compounds, e g. Co(GO)3NO. In addition to structure II for Co(CO)3NO, in which the nine electrons (cPsp) are employed in the formation of a and n bonds,... 

In spite of such deviations, the electronic balance as derived above leads to several obvious conclusions. The occurrence of single interstitial C atoms or the formation of double or single bonds in the interstitial Q units clearly indicate that the number of electrons donated by the metal framework and, hence, the number of electrons which are still available for M-M bonding conform to the ionic limit. There is evidence for an influence of the cage size on the amount of... 

These complexes are considered according to the mode of bonding of the hydrazido fragment. The known coordination types are shown in valence bond representations in Figure 15 together with the formal charge, geometry and numbers of valence electrons donated to the metal. 

Table 3.5 contains more information on the 7r-bonding in each case. There is an estimated value of the energy lowering, AAtt, and an estimate of the number of electrons transferred from the metal to the ligand, The values of A A and AjEtt are correlated now in all cases. While A A and are correlated, they are not equal. A major correction would be n, the number of electrons donated from the ligand to the metal, but there are other factors as well. 

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