This invention relates to processes for making phosphorus compounds R.sub.2P--X--PR.sub.2, R.sub.2P-M, R.sub.2P-L and R.sub.3P, and the novel cation R.sub.2P.sup.+(L)-X--P.sup.+(L)R.sub.2, where R represents an optionally substituted hydrocarbyl group, X represents a bridging group, L represents a leaving group and M represents an alkali metal atom. The invention relates further to a process for making a compound R.sub.2P-L from a compound R--H via a new process for making the compound R--Li followed by its reaction with a compound Hal.sub.2P-L. The compound R.sub.2P--X--PR.sub.2 is a ligand suitable for making catalysts for copolymerizing carbon monoxide and a olefinically unsaturated compound.