Phenylalanine – a biogenic ligand with flexible η6- and η6:κ1-coordination at ruthenium(ii) centres

Abstract

The reaction of (S)-2,5-dihydrophenylalanine 1 with ruthenium(III) chloride yields the μ-chloro-bridged dimeric η⁶-phenylalanine ethyl ester complex 3, which can be converted into the monomeric analogue, η⁶:κ¹-phenylalanine ethyl ester complex 12, under basic conditions. Studies were carried out to determine the stability and reactivity of complexes bearing η⁶- and η⁶:κ¹-chelating phenylalanine ligands under various conditions. Reaction of 3 with ethylenediamine derivatives N-p-tosylethylenediamine or 1,4-di-N-p-tosylethylenediamine results in the formation of monomeric η⁶:κ¹-phenylalanine ethyl ester complexes 14 and 15, which could be saponified yielding complexes 16 and 17 without changing the inner coordination sphere of the metal centre. The structure of η⁶:κ¹-phenylalanine complex 17 and an N-κ¹-phenylalanine complex 13 resulting from the reaction of 3 with an excess of pyridine were confirmed by X-ray crystallography.