Process for preparing tertiary phosphines containing phosphinate or phosphonate groups, and novel tertiary phosphines containing phosphinate groups

A compound of the formula (I) ##STR15## in which X is a group of the formula (Ia) ##STR16## in which Z is hydrogen, an alkali metal, the stoichiometric equivalent of an alkaline earth metal, an ammonium ion, a mono-, di-, tri- or tetraalkylammonium or a radical R.sup.4, where R.sup.4 is a C.sub.1 -C.sub.30 -alkyl radical;

• and
• R.sup.3 is a linear or branched C.sub.1 -C.sub.4 -alkyl radical;
• R.sup.1 and R.sup.2 are identical or different and are each a linear, branched or cyclic C.sub.1 -C.sub.30 -alkyl radical or C.sub.6 -C.sub.10 -aryl radical which is unsubstituted or mono-substituted to penta-substituted by C.sub.1 -C.sub.3 -alkyl radicals, or R.sup.1 and R.sup.2 together with the trivalent P atom form a dibenzophospholyl of the formula ##STR17## or a 3,4-dimethylphospholyl of the formula ##STR18##