A bidentate phosphite ligand which comprises a backbone having an a,a,a,a-tetrahydrocarbyl-1,3-dioxolane-4,5-dimethanol structure in which the hydrogen atoms of the hydroxyl groups on the methanol substituents have each been replaced by a P(OR.sup.1).sub.2 group, where R.sup.1 is an aryl radical and wherein the 1,3-dioxolane ring in the ,,,-tetrahydrocarbyl-1,3-dioxolane-4,5-dimethanol backbone is optionally substituted at the 2-position with one or more alkyl groups. When combined with a transition metal, such as nickel, the ligand provides a catalyst complex useful in hydrocyanation and other reactions.

A process for the hydrocyanation of an organic compound containing at least one olefinic group comprising reacting the organic compound with hydrogen cyanide in the presence of a catalyst complex comprising at least one transition metal and a phosphorus-containing ligand comprising a calixarene backbone and at least two aryl phosphite or aryl phosphoramidite groups chemically bonded to the backbone.

A ligand which contains arsenic and has the formula (I): where n is 2 and the ligand is bidentate; each X is O or NH; and Ar.sup.1 and Ar.sup.2 may be the same or different and each is an aryl group, provided that each Ar.sup.1 group connected to the same As atom may be combined to form a single aryl group.

A process for the hydrocyanation of an organic compound containing at least one olefinic group comprising reacting the organic compound with hydrogen cyanide in the presence of a catalyst complex comprising at least one transition metal and an organic ligand containing at least one PN linkage, wherein the P and N atoms of the PN linkage are cach bonded to two other atoms.