The reaction of (Sp)-2-(diphenylphosphino)ferrocenecarboxylic acid with carbodiimide reagents: Characterisation of the acid anhydride and urea products

Interaction of (Sp)-2-(diphenylphosphino)ferrocenecarboxylic acid [(Sp)-1] with N,N′-dicyclohexylcarbodiimide (DCC) and N-ethyl-N′-[3-(dimethylamino)propyl]carbodiimide (EDC) have been investigated in order to study the reacting system itself and to characterise side-products typically arising during the diimide-promoted condensation of acid (Sp)-1 with nucleophiles. The reaction between (Sp)-1 and DCC was found to give preferentially the respective urea derivative in the absence of a base, and (Sp)-2-(diphenylphosphino)ferrocenecarboxylic anhydride [(Sp,Sp)-3] when the same reaction was performed in the presence of 4-(dimethylamino)pyridine (DMAP). With EDC, the preference for a reaction pathway was less pronounced: whereas the reaction without the base afforded exclusively the corresponding urea, that in the presence of DMAP yielded a mixture of the urea and anhydride (Sp,Sp)-3.