The synthesis and separation of the diastereoisomeric iron complexes (+)- and (−)-C 5H 5Fe(COOC 10H 19) (CO)P(C 6H 5) 3 is described. The optically active compounds do not racemise in solution, not even at higher temperatures. In the transesterification of the menthyl esters in methanol the methyl ester C 5H 5Fe(COOCH 3)(CO)P(C 6H 5) 3 is produced in optically inactive form. As a racemisation mechanism a series of inversion steps is proposed. Using the new optically active menthyl phosphite P(OCH 2CH 2O)OC 10H 19 the diastereoisomeric compounds C 5H 5Fe(COCH 3) (CO)P(OCH 2CH 2O)OC 10H 19 were synthesised which, however, could not be separated.