Formation and reactions of bis(phosphino)succinic anhydrides

Abstract

A route to 2,3-bis(phosphino)succinic anhydrides and related compounds is described. The compounds are formed by reaction of a secondary phosphine with maleic anhydrides which bear a leaving group at the alkenic carbon atom. The reaction of bromomaleic anhydride with diphenylphosphine proceeds via diphenylphosphinomaleic anhydride. An acid-catalysed Michael addition leads to cis-2,3-bis(diphenylphosphino)succinic anhydride, which in turn rearranges to the trans isomer by an acid-catalysed process. The trans isomer was isolated as a hydrobromide. The formation of diphosphines from the corresponding maleic acids and esters has also been observed. A primary phosphine does not lead to a phosphinosuccinic anhydride.

Addition of a base to the bis(phosphino)succinic anhydride generally leads to the elimination of the phosphine moiety. However, the anhydride ring can be opened with sodium methoxide and a diphosphine, with both a carboxylic acid and a carboxylate ester moiety, is formed in moderate yield. Two conformers or isomers of this compound are obtained, both of which decarboxylate readily to give methyl 2,3-bis(diphenylphosphino)propanoate.

Co-ordination of the diphosphine system to Pt^II prevents both the elimination of secondary phosphine and the decarboxylation of carboxylic groups.