Reduction of Dioxygen by a Dimanganese Unit Bonded Inside a Cavity Provided by a Pyrrole-Based Dinucleating Ligand
✍ Scribed by Federico Franceschi; Geoffroy Guillemot; Euro Solari; Carlo Floriani; Nazzareno Re; Henrik Birkedal; Philip Pattison
- Publisher
- John Wiley and Sons
- Year
- 2001
- Tongue
- English
- Weight
- 241 KB
- Volume
- 7
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
A novel class of dinucleating ligands has been introduced into manganese chemistry to study the reactivity of this metal towards dioxygen under strictly controlled conditions. Such N 4 ligands combine some of the major peculiarities of tetradentate Schiff bases and the porphyrin skeleton. They are derived from the condensation between 2-pyrrolaldehyde and ethylenediamine or o-phenylenediamine, leading to pyr-enH 2 (LH 2 , 1), pyrophenH 2 (L'H 2 , 2) and Me 2 pyrophenH 2 , (L''H 2 , 3), respectively. Their metallation with [Mn 3 -(Mes) 6 ] (Mes 2,4,6-trimethylphenyl) led to [Mn 2 L 2 ] (4), [MnL'(thf) 2 ] (5) and [MnL''(thf) 2 ] (6). Complex 4 displays a double-stranded helical structure, while 5 and 6 are mononuclear complexes containing hexacoordinated metals. Regardless of their structure, complexes 5 and 6 behave in a similar manner to 4 in their reaction with dioxygen, namely, as a dimetallic unit inside a cavity defined by two dinucleating ligands. These reac-tions led to dinuclear Mn III /Mn IV oxohydroxo derivatives, [Mn 2 L 2 (m-O)(m-OH)] ( 7), [Mn 2 L' 2 (m-O)(m-OH)] ( 8) and [Mn 2 L'' 2 (m-O)(m-OH)] ( 9), in which the two Mn ions are strongly antiferromagnetically coupled [J À 53 (7), J À 64 (8), J À 60 cm À1 (9)]. The crystal structure of 7 could only be solved with synchrotron radiation as the crystals diffracted very poorly and suffered from twisting and disorder. The formation of 7 ± 9 has been proposed to occur through the formation of an intermediate dinuclear hydroperoxo species.