Diastereomerization Dynamics of a Bistridentate Ru^II Complex

Abstract

The unsymmetrical nature of a new tridentate ligand bis(quinolinyl)-1,3-pyrazole (DQPz) is exploited in a bistridentate Ru(II) complex [Ru(DQPz)2](2+) to elucidate an unexpected dynamic diastereomerism. Structural characterization based on a combination of nuclear magnetic resonance spectroscopy and density functional theory calculations reveals the first quantifiable diastereomerization dynamics for Ru complexes with fully conjugated tridentate heteroaromatic ligands. A mechanism that involves a large-scale twisting motion of the ligands is proposed to explain the dynamic interconversion between the observed diastereomers, and the analysis of both experiments and calculations reveals a potential energy landscape with a transition barrier for the diastereomerization of ∼70 kJ mol(-1). The structural flexibility demonstrated around the central transition metal ion has implications for integration of complexes into catalytic and photochemical applications.

Predicting Structures of Ru-Centered Dyes: A Computational Screening Tool

“…44 These are combined with other expanded cage compounds that employ both saturated, Ru(PzbPybPz) 2 (PzbPybPz = 2,6-di(pyrazol-1-ylmethyl)pyridine) 45 and Ru(DCpP) 2 (DCpP = 6- bis (2-carboxypyridyl)pyridine), 46 and aromatic, Ru(DNinP) 2 (DQinP = 2,6-di(N-7-azaindol-1-yl)pyridine), 26 extensions between the central and terminal rings. In addition, the strain in ligands can be reduced by reducing some of the aromatic rings from six-membered rings to five like in Ru(DQxP) 2 (DQxP = 2,6-di(quinoxalin-5-yl)pyridine), 26 Ru(DQPz) 2 (DQPz = 1,3- bis (8-quinolinyl)-pyrazole), 47 and in Ru(DQPl) 2 (DQPl = 1,3- bis (8-quinolinyl)-pyrrole). This extensive set of complexes gives a broad representation of ligands incorporating Ru–N bonding.…”

Chemical consequences of pyrazole orientation in RuII complexes of unsymmetric quinoline–pyrazole ligands

“…Only one oxidation feature is observed in the cyclic voltammogram with near Nernstian (63 mV) separation between the anodic and cathodic peaks. While it is not expected that the two diastereomers act as one average entity, it is clear that oxidation on top of dynamical interconversion between the isomers C-S a and C-R a 29 is not well represented by optimized individual conformation oxidation potentials. Additionally, it is possible that the redox couples of the merisomers are closer in energy than the calculations suggest due to e.g.…”

“…1. 29 Their respective enantiomers, A-R a and A-S a , as well as trans-fac-and cis-fac-isomers are schematically illustrated in Fig. S2.…”

“…Furthermore, we recently reported the bistridentate analogue mer-[Ru(DQPz) 2 ] 2+ (DQPz is bis(quinolinyl)-1,3-pyrazole, Chart 1) which displays room temperature diastereomerization between two meridional isomers. 29 The DQPz ligand is essentially a superposition of the Q1Pz and Q3PzH ligands, but with a higher relative number of quinolines. The complete pyrazole orientation series Q3PzH, Q1Pz, and DQPz, allows us to probe pyrazole orientation effects, as well as effects related to different quinoline-pyrazole ratios, on properties such as electronic absorption, electrochemical potentials and photostability by experimental and computational means.…”

Ruthenium(II) complexes bearing (NNN) ligand: catalytic evaluation of different solvent-mediated coordination modes

“…As confirmed by 1 H-NMR and ESI spectroscopy investigations two different complexes A and B were formed bearing a bidentate or tridentate ligand. [26][27][28] In the 1 On the contrary, in the presence of TEA and toluene, the tridentate complex B is obtained as evinced by the absence of the peaks belonging to p-cymene group in the 1 H-NMR spectrum. Satisfactory elemental analyses and ESI-MS data corresponding to the proposed structures were obtained for both complexes.…”