Synthesis and characterization of (Ru(II), Co(III)) heterobimetallic complexes formed with a 1,10-phenanthroline based hydroxamic acid conjugate

Abstract

A novel ambidentate type hydroxamic acid derivative (phenhaH, 1) containing an (O,O) and a 1,10-phenantroline (phen) based (N,N) donoratom set together with its heterobimetallic complexes incorporating an octahedral [Co(4 N)]³⁺ (4 N = tris(2-aminoethyl)amine (tren) or tris(2-methylpyridyl)amine (tpa)) and a half-sandwich type [(η⁶-p-cym)Ru]²⁺ entity have been synthesized and characterized using various analytical techniques. Reaction of [Co(4 N)Cl]Cl₂ with 1 proved the exclusive (O,O) coordination of the ligand to the [Co(4 N)]³⁺ core to yield [Co(tpa)(phenha)](ClO₄)₂, (2). Subsequent treatment of 1 with [Ru(η⁶-p-cym)Cl₂]₂ and [Co(4 N)Cl]Cl₂ in a one-pot reaction resulted in the formation of [(η⁶-p-cym)Ru(Cl)(phenha)Co(tren)]Cl(PF₆)₂ (3) and [(η⁶-p-cym)Ru(Cl)(phenha)Co(tpa)](PF₆)₃ (4) in which the organometallic Ru core is coordinated by the phen part while the Co entity by the hydroxamate part of 1. Cyclic voltammetry revealed that 4 could be reduced at a less negative potential and exhibits a reversible Co(III)/Co(II) redox process compared to 3 due to the π-back bonding interaction between the Co(III) centre and the pyridyl-N donors of tpa in 4. Complexes 2–4 were tested for their in vitro cytotoxicity using human-derived cancer cell lines (HeLa, MCF-7, HCT116 and MDA-MB-231) and showed moderate anti-proliferative activity in the double digit micromolar concentration range, 4 being the most active. Complex 4 displayed better activity against MDA-MB-231 cells than cisplatin.