Abstract
In the context of advancing the use of metal-based building blocks for the construction of mechanically interlocked molecules, we herein describe the preparation of late transition metal containing [2]rotaxanes (1). Capture and subsequent retention of the interlocked assemblies are achieved by the formation of robust and bulky complexes of rhodium(iii) and iridium(iii) through hydrogenation of readily accessible rhodium(i) and iridium(i) complexes [M(COD)(PPh3)2][BArF4] (M = Rh, 2a; Ir, 2b) and reaction with a bipyridyl terminated [2]pseudorotaxane (3·db24c8). This work was underpinned by detailed mechanistic studies examining the hydrogenation of 1 : 1 mixtures of 2 and bipy in CH2Cl2, which proceeds with disparate rates to afford [M(bipy)H2(PPh3)2][BArF4] (M = Rh, 4a[BArF4], t = 18 h @ 50 °C; Ir, 4b[BArF4], t < 5 min @ RT) in CH2Cl2 (1 atm H2). These rates are reconciled by (a) the inherently slower reaction of 2a with H2 compared to that of the third row congener 2b, and (b) the competing and irreversible reaction of 2a with bipy, leading to a very slow hydrogenation pathway, involving rate-limiting substitution of COD by PPh3. On the basis of this information, operationally convenient and mild conditions (CH2Cl2, RT, 1 atm H2, t ≤ 2 h) were developed for the preparation of 1, involving in the case of rhodium-based 1a pre-hydrogenation of 2a to form [Rh(PPh3)2]2[BArF4]2 (8) before reaction with 3·db24c8. In addition to comprehensive spectroscopic characterisation of 1, the structure of iridium-based 1b was elucidated in the solid-state using X-ray diffraction.
Highlights
Coordination chemistry is an increasingly prominent feature of contemporary methods for preparing mechanically interlocked molecules.1,2 In most cases metal ions are employed as well-defined templates, pre-organising the fusion of heteroatom-based molecular building blocks, but thereafter jettisoned to confer an interwoven organic product
Consistent with an unfavourable equilibrium reaction with dihydrogen, the only species observed by 1H NMR spectroscopy after freeze–pump–thaw degassing the solution is 6b
We are interested in exploring the latter as part of our ongoing research in this area
Summary
Coordination chemistry is an increasingly prominent feature of contemporary methods for preparing mechanically interlocked molecules.1,2 In most cases metal ions are employed as well-defined templates, pre-organising the fusion of heteroatom-based molecular building blocks, but thereafter jettisoned to confer an interwoven organic product. 13C{1H} NMR (126 MHz, CD2Cl2): δ 162.3 (q, 1JCB = 50, ArF), 135.4 (s, ArF), 134.5
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have