A RE(I) COMPLEX OF THE PHOSPHINE OBTAINED BY REACTING DIPHENYLPHOSPHINE WITHTERT-BUTYL ACRYLATE: A PHOSPHINE-ESTER COMPLEX THAT CAN BE CONVERTED TO THE PHOSPHINE-ACID COMPLEX UNDER MILD CONDITIONS

The base-catalyzed reaction between diphenylphosphine and tert-butyl acrylate results in the formation of Ph2PCH2CH2CO2C(CH3)3 (I). This ligand readily forms a Re(I) complex of the type fac-Re(CO)3Cl(I)2 that can be converted to the corresponding Ph2PCH2CH2CO2H complex under mild conditions by using hydrogen chloride in dioxane. Refluxing this carboxylic-acid-containing complex in acidified methanol provides the methyl ester analog of I. In contrast, this methyl ester-containing complex is stable to the ester cleavage reaction conditions used for I. Molecular mechanics calculations on I and the related methyl ester ligand provide data that are consistent with the conclusion that these phosphine-esters have cone angles that are ca. 10° smaller than that of Ph3P.