Diffusion and NOE NMR studies on the interactions of neutral amino-acidate arene ruthenium(II) supramolecular aggregates with ions and ion pairs

The interaction between [RuCl(AA)(cymene)] supramolecular aggregates (1, AA = alpha-amino-acidate = alpha-aminoisobutyrate; 2, AA = N,N-dimethyl-Gly; 3, AA = Ala; 4, AA = Pro; cymene = 4-isopropyltoluene) and ionic species derived from NBu4PF6 and KPF6 is investigated through diffusion NMR measurements and F-19,H-1-hetero-nuclear Overhauser effect spectroscopy experiments in CDCl3 and CD2Cl2. Aggregates containing the -NH2 functionality (1 and 3) interact strongly with NBu4PF6 as demonstrated by the observation of intense nuclear Overhauser effects between the fluorine atoms of PF6- and the protons of [RuCl(AA)(cymene)]. Unexpectedly, diffusion NMR measurements indicate that the average size of the aggregates increases when a small amount of NBu4PF6 is added (C-salt/C-Ru < 0.1) in CD2Cl2. At higher concentration levels of NBu4PF6 or in CDCl3, NBu4PF6 exerts a destructive effect that reduces the average size of the aggregates. [RuCl(AA)(cymene)](n) aggregates with NR-H (4) and NR2 (2) functionalities are little affected by the addition of NBu4PF6. KPF6 also interacts with [RuCl(AA)(cymene)](n) aggregates as demonstrated by the fact that it becomes noticeably soluble in CDCl3 and CD2Cl2. Diffusion H-1-NMR experiments show that the addition of KPF6 does not markedly alter the average size of [RuCI(AA)(cymene)] supramolecular aggregates. Interestingly, the average size of PF6--containing supramolecular aggregates is, in some cases, slightly higher than that of the ones that do not contain PF6-. This was deduced by independent measurements of the hydrodynamic volume of the anion and of the ruthenium complexes by diffusion F-19-and H-1-NMR experiments, respectively. Copyright (C) 2008 John Wiley & Sons, Ltd.