Hydroformylation process for producing 1,6-hexanedials

A hydroformylation process for producing a 1,6-hexanedial which comprises reacting a butadiene with hydrogen and carbon monoxide in the presence of a catalytic amount of rhodium complexed with a poly-phosphite ligand having the formula:

• ##STR9## wherein Y is a divalent organic radical that contains at least 5 carbon atoms, X is an organic radical that contains at least 12 carbon atoms, that contains at least two branched alkyl groups and that has a valence of m supplied by carbon atoms of the X radical, provided that at least two of the carbon atoms supplying the valences of the X radical are separated from each other by no more than 10 atoms and m has a value from 2 to 6 inclusive.