US Patent 7135542 Bidentate ligands for the carbonylation of unsaturated compounds

Bidentate ligand of formula (I), R1R2M1-R-M2R3R4 wherein M1 and M2 each indenpendently represent P, As or Sb; R1, R2, R3 and R4 each independently represent the same or a different optionally substituted organic group and at least one of R1, R2, R3 and R4 contains a tertiary carbon atom through which the group is linked to M1 or M2; and R represents a bridging group based on a trimethylene group connecting M1 and M2 of which the middle carbon atom is double bonded to a non-metal element chosen from group 14, 15 or 16 of the periodic table of elements. Catalyst comprising this bidentate ligand and carbonylation process n which this catalyst is used.