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Treatment of the dipeptides H&z.sbnd;Tyr&z.sbnd;Trp&z.sbnd;OH, H&z.sbnd;Trp&z.sbnd;Tyr&z.sbnd;OH, H&z.sbnd;Trp&z.sbnd;Phe&z.sbnd;OH and H&z.sbnd;Phe&z.sbnd;Tyr&z.sbnd;OH with [(η6-cymene)Ru(acetone)3]·(CF3SO3)2 (1) in CF3COOH leads to chemospecific η6-coordination in the order of electron-donating ability Trp>Tyr>Phe in respective complexes of the type [(η6-cymene)Ru(η6-dipeptide)](CF3SO3)2 (3–6) after 24–36 h at 20 °C. An analogous thermodynamic chemospecificity was also established for the complexes [(η5-Cp*)Ir(η6-dipeptide)](CF3SO3)2 (7, H&z.sbnd;Phe&z.sbnd;Trp&z.sbnd;OH; 8, H&z.sbnd;Phe&z.sbnd;Tyr&z.sbnd;OH). However, a time-dependent 1H NMR study of the reaction between [(η5-Cp*)Ir(acetone)3]·(CF3SO3)2 (2) and H&z.sbnd;Tyr&z.sbnd;Phe&z.sbnd;OH confirms an initial kinetic preference for η6-coordination of the C-terminal arene, as is also apparent from product mixtures obtained after treating 2 with H&z.sbnd;Trp&z.sbnd;Phe&z.sbnd;OH or H&z.sbnd;Trp&z.sbnd;Tyr&z.sbnd;OH for 1–2 d at 50 °C. Dinuclear sandwich complexes of the type [(η5-Cp*)Ir(μ2-H&z.sbnd;Met&z.sbnd;X&z.sbnd;OH&z.sbnd;η6-X:κ2NM, S)Pt(en)](CF3SO3)4 (9–11, X=Phe, Tyr, Trp) can be prepared in CF3COOH following initial N-terminal κ2NM, S chelation of the (en)PtII fragment by the methionine residue of the dipeptide. Chemospecific κS coordination of the [(η5-Cp*)Ir(dppz)]2+ fragment in [(η5-Cp*)Ir(dppz) (H2&z.sbnd;HArg&z.sbnd;Met&z.sbnd;NH2&z.sbnd;κS)]4+ (12), [{(η5-Cp*)Ir(dppz)}2(μ-H2&z.sbnd;Met&z.sbnd;Met&z.sbnd;OH&z.sbnd;κS:κS′)]5+ (13) and [(η5-Cp*)Ir(dppz)(μ-H&z.sbnd;Gly&z.sbnd;Met&z.sbnd;OH&z.sbnd;κS:κNG)Pt(terpy)]4+ (14) affords effective metallointercalators for DNA with binding constants Kb in the range 1.3–3.3×106 M−1 and marked melting temperature shifts ΔTm of respectively 10.2, 15.2 and 11.2 °C. [Copyright &y& Elsevier]