Rotaxane synthesis exploiting the M(i)/M(iii) redox coupleElectronic supplementary information (ESI) available: 1H, 13C{1H} and 31P{1H} NMR and ESI-MS spectra of new compounds and selected reactions. CCDC 1563158-1563164. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7dt02648j

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)(PPh 3 ) 2 ][BAr F 4 ] (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 CH 2 Cl 2 , which proceeds with disparate rates to afford [M(bipy)H 2 (PPh 3 ) 2 ][BAr F 4 ] (M = Rh, 4a [BAr F 4 ], t = 18 h @ 50 °C; Ir, 4b [BAr F 4 ], t < 5 min @ RT) in CH 2 Cl 2 (1 atm H 2 ). These rates are reconciled by (a) the inherently slower reaction of 2a with H 2 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 PPh 3 . On the basis of this information, operationally convenient and mild conditions (CH 2 Cl 2 , RT, 1 atm H 2 , 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(PPh 3 ) 2 ] 2 [BAr F 4 ] 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. In the context of advancing the use of metal-based building blocks for the construction of new and interesting mechanically interlocked molecules, we herein describe the preparation of rhodium and iridium containing [2]rotaxanes.