HYDROFORMYLATION.

Definition.  Hydroformylation is addition of hydrogen and carbonyl  group across a double bond.

Explanation . In this reaction  hydrogen and carbonyl group are added across double bond . The product will be aldehyde. This reaction was purposed by  Roelen in 1938. And mechanism was puposed by HECK and BRESLOW. The catalyst used in this reaction should homogenous and unsaturated for catalytic reaction . the catalyst used in this reaction named as Dicobalt octacarbonyl Co2(CO)8 . This catalyst is binuclear.       


general equation :      alkene + H2 + C0 →  n aldehyde / iso aldehyde 

Mechanism: When first hydrogen molecule will attack on catalyst it cause break down of main catalyst in two molecules.   


CATALYST: For catalytic  reaction catalyst should be  unsaturated and  but HCo(CO)4
follows 18 electron rule and get stable .so for unsaturation the catalyst first remove its one CO 
as a radical and make vaccant place where the alkene will react. 

Donor bonds - the bonds formed due to donation of electrons called as donor bonds.
there are three types of donor bonds.
 1- lone pair donor - bonds formed due to donation of lone pairs. 
                                                        M ⎼⎼ CO：
2 - Pi-electrons - bonds formed due to sharing of pi-electrons.
                                                        M⎼⎼⎼C2H4
3 - Sigma electron donor - bond formed due to sigma electron sharing.
                                                        M𑁋H---H
Alkene will share its pi-electrons with metal for bond formation .when alkene will attach with 
molecule then there will be a process called as alkene insertion or 1,2 migration.

 

In next step, whole alkyl group will move towards the CO and vacant its place where other 
H2, molecule  will attack. 


Next, there will attach another H2 molecule. one hydrogen will occupy vaccant place and other one
will attach with CO .
Hence there is insertion of  an  CO  and H  across double bond.

   

Disadvantages of hydroformylation -

1- linear product is more desired but chain product is dominated.