10.1021/ja9640962.s002
Emma Gallo
Emma
Gallo
Euro Solari
Euro
Solari
Nazzareno Re
Nazzareno
Re
Carlo Floriani
Carlo
Floriani
Angiola Chiesi-Villa
Angiola
Chiesi-Villa
Corrado Rizzoli
Corrado
Rizzoli
Carbon−Carbon Bonds Functioning as Electron Shuttles: The
Generation of Electron-Rich Manganese(II)−Schiff Base
Complexes and Their Redox Chemistry
American Chemical Society
1997
salophen ligand displays
electron
THF
bond
DME
Mn 2
salophen dimer
PhCH 2 Cl
Na 2
salophen 2
II
1997-06-04 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Carbon_Carbon_Bonds_Functioning_as_Electron_Shuttles_The_Generation_of_Electron-Rich_Manganese_II_Schiff_Base_Complexes_and_Their_Redox_Chemistry/3664104
The reduction of [Mn(II)-salophen] derivatives
[salophen =
<i>N</i>,<i>N</i><i> </i>‘-ethylenebis(salicylideneaminato)
dianion]
led to the formation of C−C bridged dimers. Such C−C bonds
function as two electron shuttles in electron-transfer
reactions. The reduction of
[Mn(salophen)(THF)]<sub>2</sub> (<b>1</b>) and
[Mn(3,5-Bu<sup>t</sup><sub>4</sub>salophen)(THF)]<sub>2</sub>
(<b>3</b>) with 2 equiv of sodium
metal led to the corresponding single C−C bond bridged dimers,
[Mn<sub>2</sub>(salophen<sub>2</sub>)Na<sub>2</sub>(DME)<sub>4</sub>]
(<b>5</b>) [salophen<sub>2</sub> =
C−C bonded salophen dimer] and
[Mn<sub>2</sub>(3,5-Bu<sup>t</sup><sub>4</sub>salophen<sub>2</sub>)Na<sub>2</sub>(DME)<sub>6</sub>]
(<b>7</b>), respectively. Complexes <b>5</b> and
<b>7</b> undergo
a further two electron reduction to
[Mn<sub>2</sub>(*salophen<sub>2</sub>*)Na<sub>4</sub>(DME)<sub>6</sub>]
(<b>6</b>) [*salophen<sub>2</sub>* = C−C doubly bonded
salophen
dimer] and
[Mn<sub>2</sub>(*3,5-Bu<sup>t</sup><sub>4</sub>salophen<sub>2</sub>*)Na<sub>4</sub>(DME)<sub>4</sub>]
(<b>8</b>), respectively, both containing a double C−C bridge.
The
obtention of
[Mn<sub>2</sub>{salophen(Me)CH<sub>2</sub>)}<sub>2</sub>Na<sub>4</sub>(DME)<sub>4</sub>]
(<b>9</b>) from
[Mn(salophen-Me<sub>2</sub>)(THF)]<sub>2</sub>
(<b>2</b>) strongly supports the
existence of free radical precursors in the formation of C−C bonds.
Complex <b>6</b> has been used as a source of
four
electrons in a number of reactions, thus reduction of
Ag<sup>+</sup>, PhCH<sub>2</sub>Cl, <i>p</i>-benzoquinone,
and [Co<sup>II</sup>(MeOsalen)] occurs
with the regeneration of the starting material <b>1</b>. The
C−C bond cleavage is the source of electrons, without
being
involved in any reaction as a reactive site. With stronger
oxidizing agents not only complexes <b>6</b> and <b>8</b>
transfer the
electrons stored at the C−C bonds but also the metal undergoes a
change in the oxidation state. The reaction of
<b>6</b>
with dioxygen produces a novel form of di-μ-oxo-Mn(IV) dimers,
where the salophen ligand displays a bridging
bonding mode in
[Mn<sub>2</sub>(μ-salophen)<sub>2</sub>(μ-O)<sub>2</sub>]
(<b>15</b>) and
[Mn<sub>2</sub>(μ-3,5-Bu<sup>t</sup>salophen)<sub>2</sub>(μ-O)<sub>2</sub>]
(<b>16</b>).