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Ligand and solvent control of selectivity in the C-H activation of a pyridylimine-substituted 1-naphthalene; a combined synthetic and computational study.

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posted on 08.04.2019, 14:23 by Rena Simayi, Simone M. Gillbard, Warren B. Cross, Eric G. Hope, Kuldip Singh, Gregory A. Solan
The pyridylimine-substituted 1-naphthalenes, 2-(1-C10H7)-6-{CR[double bond, length as m-dash]N(2,6-i-Pr2C6H3)}C5H3N (R = Me HLMe, H HLH), react with Na2[PdCl4] in acetic acid at elevated temperature to afford either ortho-C-Hnaphthyl activated (LMe)PdCl (2ortho) or the unactivated adduct (HLH)PdCl2 (1b). Alternatively, 1b and its ketimine analogue (HLMe)PdCl2 (1a), can be prepared by treating (MeCN)2PdCl2 with either HLMe or HLH in chloroform at room temperature. Regio-selective ortho-C-H activation to form 2ortho can also be initiated by the thermolysis of 1a in acetic acid, while no reaction occurs under similar conditions with 1b. Interestingly, the C-H activation of HLMe to give 2ortho is found to be reversible with 100% deuteration of the peri-site occurring on reacting Na2[PdCl4] with HLMe in acetic acid-d4. By contrast, heating 1a in toluene gives a 55 : 45 mixture of 2ortho and its peri-activated isomer 2peri. Pure 2peri can, however, be obtained either from (LMe)PdOAc (3peri) by OAc/Cl exchange or by the sequential reactions of 1a with firstly silver acetate then with aqueous sodium chloride. Intriguingly, a peri to ortho interconversion occurs on heating 2peri in acetic acid to give 2ortho. DFT calculations have been used to investigate the C-H activation steps and it is found that in acetic acid ortho-C-H activation is kinetically and thermodynamically favoured but peri-CH activation is kinetically accessible (ΔΔG‡ = 2.4 kcal mol-1). By contrast in toluene, the reaction appears to be irreversible with the difference in barrier height for ortho- and peri-C-H activation being very small within the error of the method (ΔΔG‡ = 0.7 kcal mol-1), findings that are in agreement with the empirically observed product distribution for 2ortho and 2peri. Single crystal X-ray structures are reported for 1a, 1b, 2ortho and 2peri.

Funding

We thank the University of Leicester for financial assistance; we also thank Nottingham Trent University for an Undergraduate Research Studentship for SMG and for the provision of computational resources. Johnson Matthey PLC are thanked for their generous loan of palladium chloride.

History

Citation

Dalton Transactions, 2018, 47 (33), pp. 11680-11690

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Chemistry

Version

AM (Accepted Manuscript)

Published in

Dalton Transactions

Publisher

Royal Society of Chemistry

eissn

1477-9234

Acceptance date

06/08/2018

Copyright date

2018

Available date

07/08/2019

Publisher version

https://pubs.rsc.org/en/Content/ArticleLanding/2018/DT/C8DT02565G#!divAbstract

Notes

Electronic supplementary information (ESI) available: Figures, tables, NMR spectra, computed Cartesian coordinates and energies, details of investigations into other reaction mechanisms. CCDC range: 1586954–1586957. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/ c8dt02565g;The file associated with this record is under embargo until 12 months after publication, in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.

Language

en

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