Nucleophile and base differentiation of pyridine with tetrahalocatechols and the formation of manganese(iii)-catecholate and pyridinium-catecholate complexes for the in situ generation of H2O2 from O2. (22nd November 2017)

• Record Type: Journal Article
• Authors: Bakewell, Nicholas; Thavarajah, Rumintha; Motevalli, Majid; Sheriff, Tippu S.
• Is Part Of: New journal of chemistry. Volume 41:Number 24(2017)
• Page Start: 15411
• Page End: 15419
• Publication Date: 2017-11-22
• Subjects: Chemistry -- Periodicals; Chimie -- Périodiques; 540
• DOI: 10.1039/c7nj02725g
• Languages: English
• ISSNs: 1144-0546

Abstract

Abstract : The structures of two novel pyridinium catecholates are reported by reaction of pyridine with tetrachloro- o -benzoquinone and tetrabromocatechol; with tetrachlorocatechol pyridine acts as a base with the structure of the pyridinium-catecholate salt reported. Abstract : Crystal structures of two novel pyridinium catecholate compounds (1, 2-dihydroxy-3, 5, 6-trichlorobenzene-4-pyridinium chloride and 1, 2-dihydroxy-3, 5, 6-tribromobenzene-4-pyridinium bromide) were obtained by the reaction of pyridine with tetrachloro- o -benzoquinone (in the presence of hydroxylamine) and tetrabromocatechol respectively. A similar reaction with tetrachlorocatechol as a starting substrate showed pyridine to act as a base rather than a nucleophile, with a crystal structure of the pyridinium-catecholate salt obtained. The role of a number of manganese-catecholate complexes as catalysts in the reduction of dioxygen to hydrogen peroxide was also investigated. Diaqua-bis(3, 5, 6-tribromobenzene-4-pyridinium catecholate)manganese(iii ) bromide·MeOH, [pyH][Mn III (Br4 Cat)2 (H2 O)(py)] and [4-MepyH][Mn III (Br4 Cat)2 (H2 O)(4-Mepy)] (where CatH2 = catechol) were synthesised and characterised by melting point, FTIR, CHN (and Mn) analysis, mass spectrometry and UV-Vis spectroscopy. All showed catalytic behaviour in dioxygen reduction at 20 ± 1 °C and pH 8.00 in the presence of hydroxylamine as reducing substrate, with initial rates of hydrogen peroxide generation and turnover frequencies of up to 11.2 × 10 −5 mol dm −3 s −1 and 8060 h −1 respectively in the presence of a 30-fold molar excess of ligand.