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Issue 30, 2019
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Hemilabile bonding of 1-oxa-4,7-dithiacyclononane in cyclometallated palladium(ii) complexes

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Abstract

The synthesis and characterization of a series of cyclometallated complexes of Pd(II) incorporating the mixed donor ligand 1-oxa-4,7-dithiacyclononane ([9]aneS2O) are presented in this study. Complexes of the form [Pd(C^N)([9]aneS2O)](PF6) (C^N = 2-phenylpyridine (ppy) 1b, 4-(2-pyridyl)benzaldehyde (ppyCHO) 2b, 7,8-benzoquinoline (bzq) 3b, 2-benzothienylpyridine (btp) 4b, 2-phenylbenzothiazole (pbt) 5b), were obtained in high-yield from a simple two-step synthetic scheme. All of these complexes were fully characterized by NMR, ESI-MS, IR, combustion analyses, and most (1b, 2b, 4b, 5b) by X-ray crystallography. Solution 1H and 13C NMR studies of [Pd(C^N)([9]aneS2O)](PF6) complexes demonstrate complicated [9]aneS2O behavior at room temperature. Variable temperature NMR reveals dynamic bonding of the [9]aneS2O ligand consistent with the presence of both endodentate and exodentate bonding modes. This is in stark contrast to the related [9]aneS3 (1,4,7-trithiacyclononane) cogeners that demonstrate fluxional endodentate bonding only in solution. X-ray structures reveal only exodenate [9]aneS2O bonding in this series, unlike the related [9]aneS3 complexes that show endodenate bonding with an axial Pd⋯S interaction. DFT calculations performed on endo and exo [9]aneS2O bonding forms of 4b, as well as a transition state calculation for interconversion, suggest reasonable access to both bonding forms based on the energy barrier. Natural bond order calculations provide further evidence for a weak axial Pd⋯O interaction in the endo form of 4b.

Graphical abstract: Hemilabile bonding of 1-oxa-4,7-dithiacyclononane in cyclometallated palladium(ii) complexes

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Supplementary files

Article information


Submitted
16 May 2019
Accepted
02 Jul 2019
First published
02 Jul 2019

Dalton Trans., 2019,48, 11520-11535
Article type
Paper
Author version available

Hemilabile bonding of 1-oxa-4,7-dithiacyclononane in cyclometallated palladium(II) complexes

D. E. Janzen, M. A. Bruening, A. A. Mamiya, L. E. Driscoll and D. A. da Silva Filho, Dalton Trans., 2019, 48, 11520
DOI: 10.1039/C9DT02059D

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