Reduction of Dioxygen by a Dimanganese Unit Bonded Inside a Cavity Provided by a Pyrrole-Based Dinucleating Ligand

Abstract

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 N4 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 pyrenH2 (LH2, 1), pyrophenH2 (L'H2, 2) and Me2pyrophenH2, (L"H2, 3), respectively. Their metallation with [Mn3-(Mes)6] (Mes = 2,4,6-trimethylphenyl) led to [Mn2L2] (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 MnIII/MnIV oxo-hydroxo derivatives, [Mn2L2(mu-O)(mu-OH)] (7), [Mn2L'2(mu-O)(mu-OH)] (8) and [Mn2L"2(mu-O)(mu-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.

Bis[4-(salicylideneamino)phenyl]methane

“…Bis-bidentate Schiff base ligands have attracted signi®cant interest as building blocks in metallo-supramolecular chemistry, especially in the synthesis of helicates (see, for example, Kruger et al, 2001;Yoshida & Ichikawa, 1997;Yoshida et al, 2000;Franceschi et al, 2001;Albrecht, 2001). The title compound, (I), has been shown to form helicate supramolecular complexes of the form [M 2 L 2 ] with transition metals (Yoshida & Ichikawa, 1997;Yoshida et al, 2000;Kruger et al, 2001).…”

Distinct M and P Helical Complexes of H2O and Metal Ions NiII, CuII, and ZnII with Enantiomerically Pure Chiral Bis(pyrrol-2-ylmethyleneamine)cyclohexane Ligands: Crystal Structures and Circular Dichroism Properties

“…[10][11][12] Despite the ongoing researches into helical structures, few examples exist of neutral compounds that adopt helical structures. [13][14][15][16] Most recently, we demonstrated that pyrrol-2-yl Schiff base ligands serve as ideal building blocks for supramolecular architectures. By variation of the spacers between two pyrrolimine units or the substituents on the pyrrole ring, multidimensional network polymers, dinuclear dimeric helicates, and trinuclear trimeric triangle and tetranuclear tetrameric square complexes were generated.…”

Coordination chemistry of a multidentate pyrrolylaldiminate ligand. X-ray crystal structure of double-helical bis-μ-[N,N′-ethylenedi(5-tert-butyl-pyrrol-2-ylaldiminate)]-dimagnesium

“…To date, compound 2 represents the third example as indicated by the Cambridge structural database. Scheme 3 depicts the magnesium compound 2 and the previously reported dinuclear copper (4) [19] and manganese (5) [18] complexes supported by the pyrrolylaldiminate ligands (L 02À ) that contain a proton rather than a t-butyl group at the 5-position. Similar to those observed in 4 and 5, complex 2 possesses a crystallographically D 2 symmetry.…”

“…Intriguing chemistry evolved from metal complexes containing these ligands has emerged extensively. In comparison, chemistry involving dianionic tetradentate pyrrolylaldiminate ligands remains relatively undeveloped [17][18][19][20][21][22][23][24]. These compounds can be regarded as a tetraaza analogue of ubiquitous salen ligands or an acyclic variation of porphyrin derivatives.…”