Abstract
3,1,2-Ruthenadicarbadodecaborane complexes bearing the [C2B9H11]2− (dicarbollide) ligand are robust scaffolds, with exceptional thermal and chemical stability. Our previous work has shown that these complexes possess promising anti-tumor activities in vitro, and tend to form aggregates (or self-assemblies) in aqueous solutions. Here, we report on the synthesis and characterization of four ruthenium(II) complexes of the type [3-(η6-arene)-1,2-R2-3,1,2-RuC2B9H9], bearing either non-polar (R = Me (2–4)) or polar (R = CO2Me (7)) substituents at the cluster carbon atoms. The behavior in aqueous solution of complexes 2, 7 and the parent unsubstituted [3-(η6-p-cymene)-3,1,2-RuC2B9H11] (8) was investigated via UV-Vis spectroscopy, mass spectrometry and nanoparticle tracking analysis (NTA). All complexes showed spontaneous formation of self-assemblies (108–109 particles mL−1), at low micromolar concentration, with high polydispersity. For perspective applications in medicine, there is thus a strong need for further characterization of the spontaneous self-assembly behavior in aqueous solutions for the class of neutral metallacarboranes, with the ultimate scope of finding the optimal conditions for exploiting this self-assembling behavior for improved biological performance.
Highlights
Metallacarborane complexes of the icosahedral type can be roughly divided into two categories: those which feature an exo-polyhedral bond to a metal ion, and those where the metal is coordinated by an approximately planar open face of the carborane cluster, e.g., the C2 B3 open face of nido-[C2 B9 H11 ]2−, commonly known as “dicarbollide” [1].Complexes belonging to the latter typically show closo structures, formally derived from the parentC2 B10 H12 clusters by replacement of a BH unit with an isolobal metal complex fragment (Figure 1), which contributes three orbitals to the cluster bonding [2]
(8) was investigated via UV-Vis spectroscopy, mass spectrometry and nanoparticle tracking analysis (NTA)
Complex 7 was synthesized in three steps from 1,2-(CO2 Me)2 -closo-1,2-C2 B10 H10 (5) (Scheme 1)
Summary
Metallacarborane complexes of the icosahedral type can be roughly divided into two categories: those which feature an exo-polyhedral bond to a metal ion, and those where the metal is coordinated by an approximately planar open face of the carborane cluster, e.g., the C2 B3 open face of nido-[C2 B9 H11 ]2− , commonly known as “dicarbollide” (see Appendix A for cluster nomenclature) [1].Complexes belonging to the latter typically show closo structures, formally derived from the parentC2 B10 H12 clusters by replacement of a BH unit with an isolobal metal complex fragment (Figure 1), which contributes three orbitals to the cluster bonding [2]. Metallacarborane complexes of the icosahedral type can be roughly divided into two categories: those which feature an exo-polyhedral bond to a metal ion, and those where the metal is coordinated by an approximately planar open face of the carborane cluster, e.g., the C2 B3 open face of nido-[C2 B9 H11 ]2− , commonly known as “dicarbollide” (see Appendix A for cluster nomenclature) [1]. Complexes belonging to the latter typically show closo structures, formally derived from the parent.
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