Novel phosphonium salts of the general formula ##STR1## wherein R.sup.1 and R.sup.2 each is a hydrogen atom or a hydrocarbon group of 1 to 12 carbon atoms which may optionally be substituted; R.sup.3 is a hydrogen atom or a hydrocarbon group of 1 to 5 carbon atoms which may optionally be substituted; R.sup.4, R.sup.5 and R.sup.6 each is a hydrocarbon group of 1 to 8 carbon atoms which may optionally be substituted; X is a hydroxyl group, a hydroxycarbonyloxy group or a lower alkylcarbonyloxy group, and processes for production of the salts are described. Telomerization catalysts containing said phosphonium salts and processes for production of straight-chained alkadienyl compounds using the same catalysts are also provided.