How -1 and 0 oxidation states of Ti are stabilized and What is Ziegler-Natta catalyst ? Give it’s use with example .

How -1 and 0 oxidation states of Ti are stabilized –explain

The element'Ti' is a second member of 3d-series of transition metal element. It’s electronic configuration and few properties are given below,

Being a member of transition element it can show variable oxidation states.The most common oxidation states  of Ti are  -2 , -1 ,  0 +2 , +3 , +4 . 

Among  this most stable and most common oxidation states is  +4.  The given oxidation states  -1  and  0 are unusually low oxidation states .  

In  low oxidation states each and every metal atom or ion are strongly  reducing and they can reduce any species which are  present around them. 

Ions or atoms which can be easily reduced can’t  remain in contact with such system .
  
Therefore   those molecules or ions which are themselves strongly reducing  and can’t  be  further reduced can stabilize such oxidation states of any metal . 

π-acid ligands like CO , NO , PX₃ , PR₃, AsR₃, 2,2- dipyridyl  etc  are very suitable for stabilization of such unusually low oxidation  states of metals . 

They are primarily electron  pair donor , that is , they act as a Lewis  base and form ligand  L-M σ-bond .  

Secondly they can receive back donated electrons from the metal  in their π- type suitable vacant orbitals. 

As a consequence the electron density around the metal  atom is considerably reduced through  such back bonding . 

In this way such low oxidation states are stabilized.Oxidation states of  -1 and  0 for Ti are known  in 2,2-dipyridyl  complex , Li [ Ti ( dipy)₃ ] and  [ Ti ( dipy ) ] respectively.  

These are prepared as back plates or purple needless respectively by  Li-reduction of TiCl₄ in presence of dipyridyl  in tetra  hydro  furan . 

These  compounds are stabilized by delocalization of electron density from the metal atom  or ion to the  aromatic ring .

What  is Ziegler-Natta  catalyst ? Give it’s use  with example .

When TiCl₄ is added to Al ( C₂H₅ )₃ in hexane , it yields a brown solid known as Ziegler-Natta  catalyst which is employed in the conversion ethene to straight chain polymer polyethene.

The probable  mechanism is as follows, 

Practice problems:

How -1 and 0 oxidation states of Ti are stabilized-explain ?

What is Ziegler-Natta  catalyst ?show one application .
What is most stable oxidation state of Ti metal and why ?

Why stable state of Cu is +2 while that of Au is +3 ?