Selective Mono- and Diamination of 2,6-Dibromopyridine for the Synthesis of Diaminated Proligands

Abstract

Selective mono- or diaminations of 2,6-dibromopyridine were performed using microwave irradiation with water as solvent in 2-2.5 h. The only significant difference between the syntheses was the inclusion of K₂CO₃ as base and CuI/DMPAO catalyst for the diaminations. The mono- and diaminations had approximately 7 and 2 g isolated yields, respectively. The monoaminated bromopyridines were attached to a TREN scaffolding molecule yielding novel ligands to support extended metal atom chain complexes.

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Structure of historically used EMAC supporting ligands: (a) 2,2′-dipyridylamine, (b) 2,6-bis­(trimethylsilylamino)­pyridine, and ligands developed herein, (c) 2,6-diaminopyridines and (d) scaffolded aminopyridines.

1. Summary of Synthetic Methods

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Partial ¹H NMR spectra of Am1–Am5 and Am7–Am8 in chloroform-d. The asterisk denotes a signal from the diaminated byproduct for Am2 and residual DBP for Am5.

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Partial ¹H NMR spectra of DAm1–4 and DAm6 in chloroform-d.

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Comparison of partial ¹H NMR spectra for TrAm1 (top), TrAm2 (middle), and TrAm3 (bottom) in chloroform-d.