Tetramethylcyclobutadiene)cobalt complexes of protected aromatic amino acids*

Reactions of [(C4Me4)Co(MeCN)3]PF6 with aromatic amino acid derivatives give the arene complexes [(C4Me4)Co(amino acid)]PF6 (amino acid = ethyl ester of N-acetylphenylalanine, N-acetyltyrosine or N-acetyltryptophan) in 75–85% yields; the structure of the tyrosine complex was determined by X-ray diffraction.