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Reduction of Dioxygen by a Dimanganese Unit Bonded Inside a Cavity Provided by a Pyrrole‐Based Dinucleating Ligand
Author(s) -
Franceschi Federico,
Guillemot Geoffroy,
Solari Euro,
Floriani Carlo,
Re Nazzareno,
Birkedal Henrik,
Pattison Philip
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010401)7:7<1468::aid-chem1468>3.0.co;2-a
Subject(s) - chemistry , ligand (biochemistry) , ethylenediamine , porphyrin , crystallography , crystal structure , reactivity (psychology) , stereochemistry , manganese , metal , photochemistry , inorganic chemistry , receptor , medicine , biochemistry , alternative medicine , organic chemistry , pathology
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 pyrenH 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 reactions led to dinuclear Mn III /Mn IV oxo‐hydroxo derivatives, [Mn 2 L 2 ( μ ‐O)( μ ‐OH)] ( 7 ), [Mn 2 L′ 2 ( μ ‐O)( μ ‐OH)] ( 8 ) and [Mn 2 L″ 2 ( μ ‐O)( μ ‐OH)] ( 9 ), in which the two Mn ions are strongly antiferromagnetically coupled [ J =−53 ( 7 ), J =−64 ( 8 ), J =−60 cm −1 ( 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.