IC-Lewis acid strengths application (1) Catlytic Properties of Cations*

Yonghe Zhang
American Huilin Institute


    As is known, olefins are bonded to transition metals and their cations via electron delocalization from the bonding π-orbital of olefin to vacant orbitals of adsorption centers (σ-bond) and from the filled d-orbitals of adsorption centers to the πk-orbital of olefin (π-bond). So only σ-bonding occurs in the case of non-transition metal cations. 

     Both σ- and π-bonding weakens the C=C bond of olefin. The former leads to a decrease in the population of its bonding orbitals and the latter increase the electron density on πk-bonding orbital’s. 

Therefore, with decreasing the charged transition-cation state and increasing the number of d electrons back-donated to the π-orbital of olefin, the surface strengths of olefin bonding to cation increase. So the bond strengths of the covalent (soft) base to the transition metal cations (the covalent or soft acids) are higher than those of non-transition cations which only σ-bonding occurs.

These results, as shown in Table 2, agree well with analysis of the literature and the data on the spectral identification of the adsorption π-complexes of olefins, reported by Efremov, et al. [21].

     For highly charged transition metal ions (e.g. M2+) we can practically neglect the contribution of π-bonding and consider the olefins adsorbed on M2+ as σ-bonded. Indeed, as shown in Table 2, the properties of such complexes are similar to those of C2H4 complexes with non-transition cations.

     As shown in Table 2, in the case of low-valence transition metal ions (M1+ and M0), the Lewis acid strength is stronger.

 

Table 2. vC=C, Lic , IC in π-complexes of ethylene with metal ions

 

 

 

   Transition meter cations     

 

 

M1+

 

 

 

M2+

 

 

 

 

vC=C

Lic

IC

 

vC=C

Lic

IC

Cu

1545

0.295

2.343

Cu

*

0.622

3.155

Ag

1570

0.384

2.147

Zn

1600

0.697

2.772

 

 

 

 

Cd

1594

0.579

2.658

 

 

Non transition meter cations

 

 

 

vC=C

Lic

IC

 

vC=C

Lic

IC

Li

1614

3.322

1.023

Ca

1610

2.05

1.617

Na

1613

2.755

1.13

Ba

1612

1.267

1.646

K

1615

2.893

0.999

 

 

 

 

 

 

On the basis of ionocovalent theory and the methods we received the same results as the experiment data concluded that vC=C and the stability of surface-complexes of olefins with transition metal ions are governed by the nature of metal and its valence state.

 

[*] Zhang, Y.Ionocovalency and Applications. 2. IC-Lewis acid strengthsJ. Am. huilin. Ins. 2011, 11, 1-10

[*] Zhang, Y. Ionocovalency, J. Am. huilin. Ins. 2011, 5, 1-11  

[*] Zhang, Y. Ionocovalency and Applications 1. Ionocovalency Model and Orbital Hybrid Scales. Int. J. Mol. Sci. 2010, 11, 4381-4406 

 

Write a comment

Comments: 0