Patent ID: 7135542

Claim:
A bidentate ligand of formula I, R 1 R 2 M 1 -R-M 2 R 3 R 4 (I) wherein M 1 and M 2 each independently represent P, As or Sb; R 1 , R 2 , R 3 and R 4 each independently represent the same or a different optionally substituted organic group and at least one of R 1 , R 2 , R 3 and R 4 contains a tertiary carbon atom through which the group is linked to M 1 or M 2 ; and, R represents a bridging group based on a trimethylene group connecting M 1 and M 2 of which the middle carbon atom is double bonded to a non-metal element selected from the group consisting of elements of groups 14, 15 and 16 of the periodic table of elements.