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Issue 3, 2014
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Synthesis, structure and dynamics of NHC-based palladium macrocycles

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Abstract

A series of macrocyclic CNC pincer pro-ligands based on bis(imidazolium)lutidine salts with octa-, deca- and dodecamethylene spacers have been prepared and their coordination chemistry investigated. Using a Ag2O based transmetallation strategy, cationic palladium(II) chloride complexes [PdCl{CNC–(CH2)n}][BArF4] (n = 8, 10, 12; ArF = 3,5-C6H3(CF3)2) were prepared and fully characterised in solution, by NMR spectroscopy and ESI-MS, and in the solid-state, by X-ray crystallography. The smaller macrocyclic complexes (n = 8 and 10) exhibit dynamic behaviour in solution, involving ring flipping of the alkyl spacer across the Pd–Cl bond, which was interrogated by variable temperature NMR spectroscopy. In the solid-state, distorted coordination geometries are observed with the spacer skewed to one side of the Pd–Cl bond. In contrast, a static C2 symmetric structure is observed for the dodecamethylene based macrocycle. For comparison, palladium(II) fluoride analogues [PdF{CNC–(CH2)n}][BArF4] (n = 8, 10, 12) were also prepared and their solution and solid-state structures contrasted with those of the chlorides. Notably, these complexes exhibit very low frequency 19F chemical shifts (ca. −400 ppm) and the presence of C–H⋯F interactions (2hJFC coupling observed by 13C NMR spectroscopy). The dynamic behaviour of the fluoride complexes is largely consistent with the smaller ancillary ligand; [PdF{CNC–(CH2)8}][BArF4] exceptionally shows C2v time averaged symmetry in solution at room temperature (CD2Cl2, 500 MHz) as a consequence of dual fluxional processes of the pincer backbone and alkyl spacer.

Graphical abstract: Synthesis, structure and dynamics of NHC-based palladium macrocycles

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Supplementary files

Article information


Submitted
18 Sep 2013
Accepted
28 Oct 2013
First published
31 Oct 2013

This article is Open Access

Dalton Trans., 2014,43, 1413-1423
Article type
Paper

Synthesis, structure and dynamics of NHC-based palladium macrocycles

R. E. Andrew and A. B. Chaplin, Dalton Trans., 2014, 43, 1413
DOI: 10.1039/C3DT52578C

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