Microwave assisted synthesis of rhodium(Ⅰ) N-heterocyclic carbene complexes and their cytotoxicity against tumor cell lines

Abstract

Organometallic rhodium(Ⅰ) complexes of the general type [(COD)(NHC)RhCl] (where COD = 1,5-cyclooctadiene, NHC = N-heterocyclic carbene) were prepared according to a two-step transmetalation method via a silver carbene intermediate. The procedure was supported by microwave irradiation allowing reduced reaction periods. The complexes were evaluated for cytotoxic effects in selected cancer cell lines, namely HT-29 colon adenocarcinoma, MDA-MB-231 breast carcinoma and MCF-7 breast adenocarcinoma, and generally triggered strong cytotoxic effects with IC50 values in the low micromolar range. Evaluation of structure-activity relationships clearly indicated a preference for branched isopropyl side chains at the nitrogen atoms of the NHC ligands versus non-branched ethyl side chains. Further studies on selected examples in HT-29 cells indicated that this could be the result of a higher cellular uptake.