Quantitative 2D EXSY and Dynamic19F-NMR Studies of the Dynamic Behaviour of the Bidentate Chelate Complex Ga(fox)3 (fox = 5-fluoro-8-hydroxyquinoline)

Stereodynamics of E/Z isomerization in rotaxanes through mechanical shuttling and covalent bond rotation

“…Such a rare phenomenon has been reported so far only for a handful of small molecules. 35 , 36 , 37 Interestingly, the two processes exhibit opposite rate dependence on solvent polarity; this selective lubrication effect can be exploited to tune the kinetics of the movements and thus change the relative contribution of each mechanism to the isomerization.…”

“…In particular, it has apparently been overlooked 33 that, in principle, these architectures can undergo E / Z isomerization through three distinct paths: (1) conformational isomerization via rotation about the covalent bond at the center of the axle, (2) co-conformational “mechanical” isomerization via ring shuttling, and (3) degenerate isomerization (i.e., an automerization reaction) 34 via concerted bond rotation and ring shuttling movements ( Figure 1 C). The presence of mechanistically distinct and entirely different isomerization paths that, in principle, could take place simultaneously represents an extremely rare occurrence in chemistry, seldom experimentally verified in small molecules 35 and metal complexes, 36 , 37 and never described in MIMs. Furthermore, the possibility of a concerted automerization path, which would entail an interplay between the rotational and mechanical shuttling motion, is interesting because geared molecular movements not only represent a fundamental consequence of stereoisomeric transformations 38 but also play a key role in the development of advanced molecular devices and machines.…”

Stereochemical assignment of the meridional isomer of the trisbidentate chelate complex Ga(fox)3 (fox = 5-fluoro-8-hydroxyquinoline) by two-dimensional correlated NMR

“…Work in this area is still in progress and will be reported elsewhere. 14 To our knowledge, no such precise assignment has been described before in such tris bidentate diamagnetic complexes.…”

“…14 The aim of this work was to assign unambiguously the three ligand spatial environments. In this paper, full 19 F, 1 H and 13 C signal assignments of the Ga(fox) 3 complex obtained using one-and two-dimensional NMR techniques are described.…”

Dynamic stereochemical rearrangements in chiral organometallic complexes

“…Use of modern DNMR techniques, particularly 2D EXSY, has enabled the twist mechanisms to be studied more fully. 78,79 In the slow exchange regime they can be distinguished by virtue of their different magnetisation transfers. Although each twist interchanges a pair of ligands three such twists, each of which permutes a different pair of ligands, Scheme 14 Mechanisms of D, L racemistaion in six-coordinate tris(chelate) complexes.…”