Issue 10, 2018

Half-sandwich type rhodium(iii)–aminohydroxamate complexes: the role of the position of the amino group in metal ion binding

Abstract

Complex formation equilibria between [(η5-Cp*)RhIII(H2O)3]2+ and aminohydroxamic acids (L-2-amino-N-hydroxyacetamide (α-alahaH), 3-amino-N-hydroxypropanamide (β-alahaH) and 4-amino-N-hydroxybutanamide (GABAha, γ-abhaH)) having the primary amino group in different chelatable positions relative to the hydroxamic function were studied using pH-potentiometric, 1H NMR and ESI-MS methods and the formation constants of the complexes present in aqueous solution are reported. The relative order of the pH-dependent conditional stability of the hydroxamate type (O,O) and (Namino,Nhydroxamato) chelates was found to determine to a great extent the coordination modes both in the mono- and various dinuclear species formed. While with α-alaha, a 5-membered (N,N) chelated mononuclear complex predominates, with β-alaha in a wide pH-range, very stable dinuclear cluster ions exist. With γ-abha, in the most stable complexes, two ligands (in reverse variation) link two half-sandwich cations, coordinating each ligand via the hydroxamate chelate to one metal centre, while via the amino-N to the other one. This arrangement seems to be further stabilized by a hydrogen bond as DFT calculations support the extra stabilization effect of internal H-bonding in [{(η5-Cp*)RhIII}2H−1(γ-abha)2]+. The synthesis, spectral (NMR and IR) and MS characterization of a novel complex with an iridium analogue, [(η5-Cp*)IrIII(α-alaha)Br] (1) is also described. This complex was tested for its in vitro cytotoxicity using human-derived cancer cell lines (A2780, HeLa, DU-145, A549, and MCF-7) and showed insignificant anti-proliferative activity in the micromolar concentration range.

Graphical abstract: Half-sandwich type rhodium(iii)–aminohydroxamate complexes: the role of the position of the amino group in metal ion binding

Supplementary files

Article information

Article type
Paper
Submitted
30 Nov 2017
Accepted
12 Mar 2018
First published
12 Mar 2018

New J. Chem., 2018,42, 7659-7670

Half-sandwich type rhodium(III)–aminohydroxamate complexes: the role of the position of the amino group in metal ion binding

P. L. Parajdi-Losonczi, P. Buglyó, H. Skakalova, J. Kasparkova, N. Lihi and E. Farkas, New J. Chem., 2018, 42, 7659 DOI: 10.1039/C7NJ04711H

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