136
Published on the web January 23, 2010
2¹
Identification of a Discrete Peroxide Dianion, O2 , in a Two
Sodium-(1,6-Anhydro-¢-maltose)2-Peroxide Complex
Takayuki Kato,1 Takashi Fujimoto,2 Ayumi Tsutsui,1 Mitsuru Tashiro,1 Yoshihiro Mitsutsuka,1 and Tomoya Machinami*1,2
1Department of Chemistry, College of Science and Technology, Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-8506
2Frontier Research Center for Environmental Science, Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-8506
(Received November 30, 2009; CL-091063; E-mail: machinam@chem.meisei-u.ac.jp)
A complex formed by two 1,6-anhydro-¢-maltoses with
by the use of 30% aqueous hydrogen peroxide with sodium
hydroxide. The yield of 2 from parent 1 achieved over 80% when
excess hydrogen peroxide was used.8 The complex formation
with 1 in the presence of Na shows an exclusive system to capture
peroxide dianions and preserve them as intact dianions.
peroxide and two sodium ions has been isolated and determined
to be [Na2(1,6-anhydro-¢-maltose)2(H2O)3]O2 by X-ray crystal-
lography. The O2 moiety, 1.496(2) ¡ for the O-O distances in
the complex was identified as a discrete peroxide dianion,
whereas two sodium and two carbohydrate molecules constitute
a binuclear complex counter cation.The complex containing the
discrete peroxide dianion was proven to be a useful oxidizing
agent, which successfully oxidized ¡,¢-unsaturated ketone to
epoxyketone.
Crystal structure determination9 revealed a novel binuclear
complex cation, (1,6-anhydro-¢-maltoses)2Na2, and an intact
2¹
peroxide dianion, O2 , becoming immobilized within the
hydrogen-bond networks between two binuclear complexes
(Figure 1). The peroxo group, 3.96-4.05 ¡ away from sodium
ions, and the O-O bond and the line of Na£Na are perpendicular
to each other. The sodium ions are seven-coordinated in a
pentagonal bipyramid with seven Na+£O distances ranging 2.31
to 2.68 ¡. Four of these Na+£O bonds are from one 1,6-
anhydro-¢-maltose (1), including the glycosidic oxygen atom,
and two are from another anhydro sugar molecule (Figure 2).
This coordination sphere of Na is similar with that of [Na(18-
crown-6)H2O]SCN. For 1,6-anhydro sugar 1, it provides O-2¤,
-1¤, 5, 2 as a triethylene glycol array to coordinate with one Na+
and O-3¤, -2¤ as a ethylene glycol array to coordinated with
another Na+, thus O-2¤ is shared for the coordination around
both sodium ions (Figure 1). Remaining one Na+£O bond is
from the water molecule, which is shared by two pentagonal
bipyramids and completes the binuclear complex. Such a
structure is provided as a result of the complex formation with
the peroxide dianion. The O-O (1.49 ¡) distance in the complex
is exclusively adapted with the accepted value for the pure ionic
peroxide.6 The peroxide dianion is surrounded by six hydroxy
groups, three for each oxygen, from four carbohydrate molecules
During our work1 to study the specific complex formation of
1,6-anhydro sugar2 prepared from corresponding free sugar
through intramolecular dehydration, a complex of 1,6-anhydro-
¢-maltose (1) with sodium ion was obtained under alkaline
conditions. The complex was identified as a 1:1 ratio of anhydro
sugar with sodium ion by ion chromatography and elementary
analysis. The repeated crystallization of the 1,6-anhydro-¢-
maltose-sodium complex under alkaline conditions afforded
only a small amount of single crystals, whose structure was
suggested to be [Na2(1,6-anhydro-¢-maltose)2(H2O)3]O2 (2) by
initial X-ray crystallographic analysis. The peroxide complex
might be afforded from accidental oxidation, and the O2 moiety
in the complex must be present as the peroxide dianion in order
to maintain the charge balance. The dianion is immobilized
within the complex crystal.
The peroxide dianion has been generally reported for
organometallic peroxides recently. A heterocyclic organogal-
lium peroxide has been synthesized, and the peroxo ligand with
a O£O distance of 1.481 ¡ in the complex was identified as
peroxide dianion.3 Such a situation with a dioxygen ligand
coordinated by two metal atoms is well argued for transition-
metal compounds including proteins.4 The peroxide dianion was
reported for lithium peroxo bicyclic guanidines and lithiated
guanidinate,5 and the O£O distances in the complexes (1.501
and 1.505 ¡) are suggested to be approaching the accepted
value of 1.49 ¡ for purely ionic group 1 peroxides.6 Since a
chracteristic feature of the peroxide with the O£O distance of
1.496(2) ¡ in the complex 2 is suggested to be purely ionic when
compared with those in organometallic peroxides, the reprodu-
cible generation of the complex was conducted by the use
of sodium peroxide. An aqueous solution of 1,6-anhydro-¢-
maltose (1) was mixed with an equivalent amount of solid
Na2O2, and then 2-propanol was gradually added to the resulting
solution. Although a considerable loss of oxygen was observed
when solid Na2O2 was dissolved in water, single crystals of 2
were deposited with up to 33% yield from 1. For the peroxide,
33% of O2 in parent Na2O2 was immobilized within the complex
crystals 2.7 The reproducible generation of 2 was observed even
2¹
with six O2 £(H)O distances ranging 2.47 to 2.57 ¡ (Figure 3).
2¹
Two of these O2 £(H)O bonds are from the binuclear com-
plex counter cation, and four are from two adjacent binuclear
Anhydro
sugar (A)
O5'
C1'
C4
O1'
C5
C5
Na1
O1'
-
C4
Na2
O
Anhydro
sugar (B)
-
C1'
O
O5'
Figure 1. Structure of the [Na2(1,6-anhydro-¢-maltose)2-
(H2O)3]O2.
Chem. Lett. 2010, 39, 136-137
© 2010 The Chemical Society of Japan