Anionic carbonato and oxalato cobalt(III) nitrogen mustard complexes

Synthetic approaches to cobalt(III) complexes Co(L)(L')2] containing the bidentate dialkylating nitrogen mustard N,N-bis(2-chloroethyl)-1,2-ethanediamine (L = dce) together with anionic ancilliary ligands (L') which are either carbonato (CO3(2-)), oxalato (ox2-), bis(2-hydroxyethyl)dithiocarbamato (bhedtc-), 2-pyridine carboxylato (pico-) or 2-pyrazine carboxylato (pyzc-) were investigated. Synthetic routes were developed using the related amines N,N-diethyl-1,2-ethanediamine (dee) and 1,2-ethanediamine (en). The complexes Co(CO3)2(L)]- (L = dee 1, dce 2), Co(ox)2(L)]- (L = dee 3, dce 4), Co(bhedtc)2(dee)]+ 5, Co(bhedtc)2(en)]+ 6, mer-Co(pico)3], mer-Co(pyzc)]3 7 and Co(pico)2(dee)]+ 8 were prepared and were characterised by IR, UV-Vis, 1H and 13C1H] NMR spectroscopy, mass spectrometry and cyclic voltammetry. Co(bhedtc)2(en)]BPh4 6b and trans(O)-Co(pico)2(dee)]ClO4 8 were characterised by X-ray crystallography. In vitro biological tests were carried out on complexes 1-4 in order to assess the degree to which coordination of the mustard to cobalt attenuated its cytotoxicity, and the differential toxicity in air vs. nitrogen.