Pillared cobalt complexes for oxygen separation

The present invention is a cobalt complex having the structural formula: ##STR1## wherein each R.sub.1 is independently, a phenyl or a C.sub.1 -C.sub.6 alkyl group; each R.sub.2 is independently hydrogen, a phenyl, or a C.sub.1 -C.sub.6 alkyl group; R.sub.3 is either N-succinimido substituted with a C.sub.3 or greater hydrocarbon functionality at the carbon atoms .alpha. to the imido carbonyl carbons, or a carbonyl functionality having a C.sub.1 greater hydrocarbon substituent with the proviso that if said substituent is methyl, R.sub.2 cannot be hydrogen; and Y is o-phenylene, --CH.sub.2 --.sub.a, wherein "a" is 2 or 3, --CH.sub.2 --.sub.b NR.sub.4 --CH.sub.2 --.sub.c, wherein "b" and "c" are independently 2 or 3 and R.sub.4 is hydrogen or a C.sub.1 -C.sub.12 alkyl group. These complexes have the ability to selectively and reversibly bind oxygen, thus making them useful components of oxygen separation membranes and absorbents.

TECHNICAL FIELD OF THE INVENTION 
The present invention relates to metal complexes that reversibly react with 
molecular oxygen and are suitable for use in air separation processes. 
BACKGROUND OF THE INVENTION 
Oxygen is produced industrially in enormous quantities from air. Currently, 
a majority of industrially-produced oxygen is separated from air by 
condensing the air and then fractionally distilling the liquid air to 
separate the oxygen from nitrogen and other gases. This liquefaction 
procedure consumes very large amounts of energy, since the boiling point 
of oxygen at atmospheric pressure is only 77.degree. K. 
In view of the known disadvantages of the air liquefaction process, 
attention has recently been directed toward methods for the separation of 
oxygen from air at temperatures much closer to ambient. In principle, such 
separation methods are very simple; a solution is prepared containing a 
compound which can complex molecular oxygen in a manner similar to that of 
the known biological oxygen-complexing proteins, myoglobin and hemoglobin, 
this solution is exposed to air or a similar oxygen-containing gas such 
that a large proportion of the oxygen-complexing compounds become 
complexed with oxygen. The solution is then removed from contact with the 
air and exposed to an environment induced by pressure or temperature 
changes in which the oxygen partial pressure is less than that in 
equilibrium with the oxygen-complexed compound, so that the compound gives 
up at least part of its oxgyen, thereby releasing into the environment a 
gas much richer in oxygen than that with which the solution was originally 
in contact. 
One technique for separating oxygen from air involves the use of 
"immobilized liquid membranes". Such immobilized liquid membranes comprise 
a solid support, typically a synthetic polymer which is inert to oxygen, 
together with liquid immobilized within the inert support. The support may 
have very fine pores therein so that the liquid is contained therein by 
capillary forces, a polymer film acting as the support may be swollen by 
contact with the liquid to form a gel or various other techniques may be 
used for immobilizing the liquid within the support. Air or some other 
oxygen-containing gas is passed over one side of the immobilized liquid 
membrane, while the gas which passes through the membrane is removed by 
pumping on the opposite side of the membrane. The oxygen "diffuses 
selectively" through the liquid membrane, due to the presence of an oxygen 
partial pressure gradient between the two sides of the membrane. The 
oxygen molecules are carried in the form of a metal complex through the 
immobilized liquid membrane at a much greater net transport rate than the 
rate in which other gases are passed through the membrane. One such 
membrane system is disclosed in U.S. Pat. No. 3,396,510 which discloses a 
facilitated transport system using a liquid membrane and a non-volatile 
species which is soluble in the immobilized liquid which reversibly reacts 
with a specific gaseous component to be separated from the gaseous 
mixture. Although the patent discloses the possibility of facilitated 
transport of oxygen, the proposed system is primarily an aqueous-based 
one, utilizing water soluble complexing agents, and was found to be 
commercially unfeasible. 
Daryle H. Busch, et al. in an article entitled "Molecular Species 
Containing Persistent Voids. Template Synthesis and Characterization of a 
Series of Lacunar-Nickel Complexes in the Corresponding Free Ligands", in 
J. Am. Chem. Soc. 103 pp 1472-1478 (1981), discloses a family of lacunar 
ligands synthesized in the form of nickel (II) complexes by a template 
process. The species disclosed were designed to provide a "lacuna" or 
protective void, or cavity, in the vicinity of a coordination site in 
order to facilitate the binding of small molecules to the metal ions. The 
species of complexes are characterized by having four N-atoms bound to a 
single nickel atom in a ligand system which results in an overall +2 
charge for the complex. 
Kuninobu Kasuga, et al. in an article entitled "A Preparation and Some 
Properties of Cobalt (II) Schiff-base Complexes and Their Molecular Oxygen 
Adducts", Bull. Chem. Soc. Jpn. 56, pp 95-98 (1983) disclose seven new 
cobalt (II) complexes with a tetradentate Schiff-base ligand and their 
three oxygen adducts. The disclosed complexes are reported to be stable at 
room temperature for several weeks and have the characteristic of having 
favorable affinity for molecular oxygen. 
Roman, in U.S. Pat. Nos. 4,451,270 and 4,542,010 disclose processes and an 
apparatus for the separation and purification of oxygen and nitrogen. The 
processes utilize novel facilitated transport membranes to selectively 
transport oxygen from one gaseous stream to another, thereby leaving 
nitrogen as a by-product. In accordance with this process, an oxygen 
carrier capable of reversibly binding molecular oxygen is dissolved in a 
polar organic solvent and the resulting carrier solution is contained 
within a membrane which separates a gaseous feed stream, such as 
atmospheric air, to form a gaseous product stream. The oxygen carriers 
employed in the disclosed process are metal-containing complexes wherein a 
metal is bound by four ligating atoms, and has the capacity to reversibly 
bind oxygen and is also soluble in various polar organic solvents and 
reactive with axial bases. 
U.S. Pat. No. 4,584,359 discloses a membrane of a vinyl polymer which 
contains oxygen-transferring groups not in solution, but in a chemically 
bonded form, which is used for separating molecular oxygen from a mixture 
of gases. 
BRIEF SUMMARY OF THE INVENTION 
The present invention is a class of pillared cobalt complexes which are 
capable of reversibly reacting with molecular oxygen. The cobalt complexes 
have the general structural formula: 
##STR2## 
wherein each R.sub.1 is independently, a phenyl or a C.sub.1 -C.sub.6 
alkyl group; each R.sub.2 is independently hydrogen, a phenyl or a C.sub.1 
-C.sub.6 alkyl group; R.sub.3 is either N-succinimido substituted with a 
C.sub.3 or greater hydrocarbon functionality at the carbon atoms .alpha. 
to the imido carbonyl carbons, or a carbonyl functionality having a 
C.sub.1 or greater hydrocarbon substituent with the proviso that if said 
substituent is methyl, R.sub.2 cannot be hydrogen; and Y is o-phenylene, 
--CH.sub.2).sub.a wherein "a" is 2 or 3, --CH.sub.2).sub.b NR-- 
--CH.sub.2).sub.c, wherein "b" and "c" are independently 1, 2 or 3 and 
R.sub.4 is hydrogen or a C.sub.1 -C.sub.12 alkyl group. The cobalt 
complexes described above have wide utility in oxygen separation 
operations. For example, the complex can be added to a solvent to form an 
oxygen adsorption medium, or can be present as an O.sub.2 carrier in a 
gas-separation membrane.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is a new class of cobalt complexes which are useful 
in oxygen separation processes. The new class of complexes differ from 
prior art complexes in that the structures of the new complexes enable 
them to achieve relatively long life and good O.sub.2 affinity at near 
ambient temperatures. 
The new class of cobalt complexes are pillared Schiff-base complexes having 
the general structural formula: 
##STR3## 
The structure is characterized by the presence of two keto-imine chelate 
ring moieties, joined by the linkage denoted by "Y" and having 
substituents R.sub.1, R.sub.2 and R.sub.3. The substituent adjacent to 
each keto group, R.sub.1, is independently, a phenyl or a C.sub.1 -C.sub.6 
alkyl group. The substituent adjacent to the imine group on each 
keto-imine moiety, R.sub.2, is independently hydrogen, a phenyl or a 
C.sub.1 -C.sub.6 alkyl group. "Y" may either merely serve to link the two 
keto-imine moieties, in which case Y is either o-phenylene or 
--CH.sub.2).sub.a where "a" is 2 or 3; or Y may also contain a fifth 
ligating atom, in which case Y is --CH.sub.2).sub.b NR.sub.4L 
(CH.sub.2).sub.c, wherein "b" and "c" are independently 1, 2 or 3 and 
R.sub.4 is hydrogen or a C.sub.1 -C.sub.12 alkyl group. 
Critical components of the present structure are the R.sub.3 groups. Both 
R.sub.3 groups are bulky groups which are generally oriented perpendicular 
to the plane of the Schiff-base ligand and provide a "pillaring" effect 
which protects against peroxo-bridged dimer formation. Consequently, the 
presence of bulky R.sub.3 groups enhance the selectivity toward the 
formation of monomeric O.sub.2 complexes. Each R.sub.3 is either 
independently N-succinimido substituted with a C.sub.3 or greater 
hydrocarbon functionality at the carbon atoms .alpha. to the imido 
carbonyl carbons, or R.sub.3 is a carbonyl functionality having a C.sub.1 
or greater hydrocarbon substituent. The larger the R.sub.3 group the 
greater the "pillaring" effect, however, for ease for synthesis and 
diffusion characteristics in membrane systems, it is often preferred that 
R.sub.3 not be too large. Suitable examples of R.sub.3 groups include 
carbonyl functionalities having the structural formula COR.sub.5 wherein 
R.sub.5 is phenyl, naphthyl, antharcyl, and fluorocarbon among others. 
Additionally, N-succinimido derivatives such as phthalimido are also well 
suited. While each R.sub.3 group is independent of the other, for ease of 
synthesis, it is preferred that both R.sub.3 groups of a single complex 
have the same structure. 
The presence of the R.sub.1 and R.sub.2 groups serve to orient the R.sub.3 
group perpendicular to the plane of the ligand so as to achieve the 
"pillaring" effect. Consequently, it has been found that if R.sub.3 is a 
smaller bulky group, i.e., a carbonyl functionality having a methyl 
substituent, R.sub.2 must be C.sub.1 or greater (i.e., R.sub.2 cannot be 
hydrogen), to achieve sufficient pillaring effect to adequately prevent 
dimer formation. 
All of the above described groups may have one or more suitable organic or 
inorganic substituents such as methyl, ethyl, halogens, etc. The above 
structure provides a small, neutrally charged complex which allows for 
good diffusion characteristics. Additionally, the presence of the 
election-withdrawing groups adjacent to the carbonyl carbons increases the 
resistance of the complexes to autoxidation. Further, the R.sub.3 groups, 
militates against formation of bridged peroxy compounds which form 
irreversibly in previously known Schiff-base oxygen complexes. 
The present cobalt complexes reversibly bond oxygen, and because of their 
favorable longevity and diffusion characteristics, are well suited for use 
in a wide variety of oxygen separation processes. Specifically, the 
complexes can be used in the presence of a solvent as a selective 
absorbent for oxygen to separate oxygen from other gaseous components; 
e.g., nitrogen, argon, etc. Alternatively, the complexes can be used as 
mobile O.sub.2 carriers in gas-separation membranes. One specific 
embodiment comprises an immobilized liquid membrane containing the oxygen 
carrier as a mobile species. 
An oxygen-containing gas mixture is brought into contact with the cobalt 
complex for a time sufficient for at least a portion of the oxygen to bind 
with the complex. The bound oxygen is subsequently released from the 
complex and recovered as product. The oxygen can be released by various 
means such as pressure differential, temperature differential, or any 
other suitable means. In cases in which the cobalt complexes are 
incorporated into membrane structures, the oxygen is transported across 
the membrane and subsequently released on the side opposite the feed. 
In addition to the longevity and diffusion properties, the most fundamental 
property of the complex is oxygen affinity, as expressed by the 
equilibrium binding constant, KO.sub.2, for the reaction: 
##STR4## 
wherein LnCo represents the cobalt complex. 
Typically KO.sub.2 is expressed as K (torr.sup.-1) which is calculated: 
##EQU1## 
The value for K therefore is the reciprocal of the pressure at which 1/2 of 
the available complex will be bound with oxygen at a given temperature. 
The cobalt complexes of the present invention have good oxygen affinity 
e.g., K (torr.sup.-1) between 10.sup.-1 and 10.sup.-3 at ambient 
temperature and pressure, and also exhibit good oxygen affinity at varying 
conditions. 
The present oxygen complexes can be used as oxygen absorbents in any 
suitable solvent. Solvents found to be useful in the present invention are 
generally organic liquids or mixtures of organic liquids which are 
preferably polar, although non-polar liquids may be useful in some cases. 
In other cases, the solvent may comprise a mixture of organic liquids in 
water. The solvent must be able to dissolve a sufficient concentration; 
e.g., preferably in excess of 0.05M, of the complex. Classes of useful 
solvents include: lactones, lactams, sulfoxides, nitriles, amids, amines, 
esters, ethers and other nitrogen-containing liquids. In cases in which 
the cobalt complex in solution has a structure wherein "Y" does not 
contain a N-atom, an "axial-base" may have to be added to the solution if 
such a base is not a component of the solvent, itself. Such axial-bases 
provide an additional coordinating atom to those contained in the oxygen 
carrier, which assists in the reversible binding of the oxygen. Classes of 
axial bases found useful are imidazoles, ketones, amides, amines, 
sulfoxides, pyridines, etc. 
Although the two most common applications for the present complexes are in 
membrane structures or in solution as absorbents, their stability makes 
them suitable for other possible applications, such as, components of 
solid state membranes, or for use in "air" batteries where gaseous O.sub.2 
forms part of one electrode. 
Synthesis of the cobalt complex is typically carried out by preparing a 
precursor nickel or copper compound wherein the nickel or copper is bound 
to two oxygen and two nitrogen atoms. The precursor compound then 
undergoes demetallation to remove the nickel or copper and form a free 
ligand. The free ligand is subsequently reacted with a source of cobalt to 
form the cobalt complex. The examples below illustrate specific techniques 
for synthesizing various pillared cobalt complexes and the use of these 
complexes in binding oxygen. These examples are only illustrative and are 
not meant to limit the scope of the present invention. 
EXAMPLES 
Various pillared cobalt complexes as described above were synthesized. All 
the experiments were carried out under moisture-free conditions. Initially 
three different precursor complexes (I, II and III) were prepared having 
the structural formula: 
##STR5## 
wherein (I) R.sub.7 .dbd.CH.sub.3 ; R.sub.8 .dbd.H; 
Y.dbd.--CH.sub.2).sub.2 ; M.dbd.Ni 
(II) R.sub.7 .dbd.R.sub.8 .dbd.CH.sub.3 ; Y.dbd.--CH.sub.2).sub.2 ; 
M.dbd.Cu or Ni 
(III) R.sub.7 .dbd.R.sub.8 .dbd.CH.sub.3 ; Y.dbd.(CH.sub.2).sub.3 
##STR6## 
M.dbd.Cu. The precursors were formed by known literature routes, such as 
taught by L. Wolf, et al. Anorg. Allg. Chem., 1966, 346, 76; Y. Chen, et 
al. Inorg. Chem., 20, 1885 (1981) and P. J. McCarthy, et al. J. Am. Chem. 
Soc. 1955, 77, 5820. 
The acid chloride, m-anisoyl chloride, was obtained from Aldrich Chemical 
Company. Benzene and triethylamine were dried over CaH.sub.2 and then 
distilled. 
EXAMPLE 1 
Synthesis of a pillared cobalt complex wherein: 
##STR7## 
(a) 1.90 gm (6.77 mmole) of the precursor complex, (II), M.dbd.Ni was 
dissolved in 200 ml of dry benzene. To this, 1.37 gm (13.54 mmole) of 
triethylamine was added, followed by 2.30 gm (13.54 mmole) of m-anisoyl 
chloride. The mixture was refluxed for three days with stirring. The 
triethylamine hydrochloride was filtered and the solvent was removed on a 
rotary evaporator. The contents of the flask were dissolved in a minimum 
volume of chloroform and chromatographed on an alumina column. A fast 
moving orange-red band was collected by eluting with chloroform. Addition 
of ethanol, followed by reduction in the volume of the solvent, resulted 
in the precipitation of the pillared nickel complex. Yield: 2.80 gm (5.10 
mmoles, 75%). 
One gram (1.82 mmole) of the pillared nickel complex was reacted with 0.8 
gm of p-toluene sulfonic acid in acetonitrile with gentle warming. The 
color of the solution immediately became green. After removal of all the 
solvent by rotary evaporation, water was added to precipitate an oily 
yellow solid. Chloroform was added to dissolve the solid and the solution 
was dried with anhydrous sodium sulfate. Reduction of the volume of the 
solvent followed by the addition of diethyl ether resulted in the 
formation of a pale yellow solid. The .sup.13 C nmr of this solid was 
identical to that of the free ligand obtained by the demetallation of the 
pillared copper complex. Yield: 0.60 gm (1.21 mmole, 66%). 
(b) The pillared cobalt complex was prepared by the following procedure. 
0.40 gm (0.80 mmole) of the free ligand was reacted with 0.24 gm (0.96 
mmole) of cobalt acetate monohydrate and 0.077 gm (1.92 mmole) of sodium 
hydroxide in methanol. Gentle reflux for a few hours yielded an orange 
solution and a bright yellow precipitate. The yellow precipitate was 
filtered and recrystallized from methylene chloride and methanol to get 
.apprxeq.200 mg of product. The filtrate, on long standing, gave another 
100 mg of product. Overall yield: 0.30 gm (68%). Infrared: C.dbd.O (1650 
cm.sup.-1) strong. 
EXAMPLE 2 
Synthesis of a pillared cobalt complex wherein: 
##STR8## 
(a) 0.73 gm (2.89 mmoles) of the precursor complex, (II), M.dbd.Ni was 
dissolved in 125 ml of dry benzene. To this, 0.82 ml of triethylamine was 
added, followed by 0.82 ml of m-anisoyl chloride. After refluxing for 60 
hours, the solution was filtered to remove triethylamine hydrochloride, 
and rotovaped to dryness. The contents of the flask were dissolved in a 
minimum volume of chloroform and chromatographed on an alumina column. A 
fast moving orange-red band was eluted with chloroform. Ethanol was added 
to the solution and the volume was reduced on a rotary evaporator. This 
resulted in the precipitation of the orange-red product. Yield: 1 gm (1.91 
mmole, 65%). 
(b) The desired pillared cobalt complex was synthesized from the resultant 
nickel complex in accordance with the procedures set out in step (b) of 
Example 1 above. 
EXAMPLE 3 
Synthesis of a pillared cobalt complex wherein: 
##STR9## 
(a) 1.298 gm (3.5 mmole) of the precursor complex, (III), M.dbd.CU was 
dissolved in 120 ml of dry benzene containing 1 ml of triethylamine. 1.194 
gm (7.0 mmole) of m-anisoyl chloride was dissolved in benzene and added 
over a period of 40 minutes. The solution was stirred a room temperature 
over a period of 48 hours. The white precipitate of triethylamine 
hydrochloride was filtered. The benzene was removed on a rotary evaporator 
and the resulting oil was dissolved in petroleum ether. Upon cooling, the 
pillared copper complex was obtained as a green powder in 98% yield. 
The complex (1.2 gm) was dissolved in 100 ml of dry chloroform. Hydrogen 
sulfide was bubbled for ten minutes and the copper sulfide precipitate was 
filtered over celite. The solvent was removed under vacuo to get a yellow 
oil that was identified as the pillared free ligand by .sup.13 C nmr. 
(b) 0.3532 g (0.61 mmole) of the ligand synthesized in step (a) was 
suspended in .apprxeq.50 ml of dry t-butyl alcohol. To this, 0.389 gm 
(0.61 mmole) of (Et.sub.4 N).sub.2 CoBr.sub.4 was added, followed by 0.137 
gm (1.2 mmole) of potassium t-butoxide; at this point the solution turned 
red-brown. The solution was stirred for 21/2 hours and the solvent was 
removed under vacuo, 200 ml of dry benzene was added, stirred for two 
hours and then filtered. The solvent was removed and the products 
recrystallized from CH.sub.2 Cl.sub.2 /pet ether to get a dark yellow 
powder. Yield: 65%; IR, 1630 cm.sup.-1 (C.dbd.O) strong. 
EXAMPLE 4 
To demonstrate the utility of the present pillared cobalt complexes for 
binding oxygen, the complex synthesized in Example 1 above was dissolved 
in a solution containing 2% pyridine in toluene. The solution was 
contacted with a gas stream containing nitrogen and oxygen at -15.degree. 
C. The binding constants (KO.sub.2) with oxygen for the complex were 
calculated, and the results are reported below. 
______________________________________ 
Wavelength* (nm) 
KO.sub.2 (torr.sup.-1) 
Standard Deviation 
______________________________________ 
370 2.574 0.433 
360 2.865 0.424 
350 3.031 0.432 
342 3.160 0.447 
______________________________________ 
*Wavelength of light used to measure the concentration of oxygenated and 
unoxygenated complex. 
A KO.sub.2 of 3.0 (torr.sup.-1) = P1.sub./.sbsb.2 (O) = 1.sub./.sbsb.3.0 
0.33 torr 
The above results indicate that at -15.degree. C., 1/2 of the complex will 
be bound with oxygen at a pressure of only 0.33 torr. Increasing the 
pressure will result in more oxygen being bound while decreasing the 
pressure will cause the oxygen to be released. 
EXAMPLE 5 
The pillared cobalt complex synthesized in Example 3 was dissolved in 
toluene, and the resulting solution was contacted with a gas stream 
containing nitrogen and oxygen at -20.degree. C. The binding constants 
(KO.sub.2) with oxygen for the complex were calculated, and the results 
are reported below. 
______________________________________ 
Wavelength (nm) KO.sub.2 (torr.sup.-1) 
______________________________________ 
350 12.4 .+-. 0.8 
360 12.6 .+-. 0.8 
370 13.0 .+-. 0.9 
380 12.8 .+-. 0.9 
400 12.6 .+-. 0.9 
______________________________________ 
The above results indicate that at low temperatures, the complexes have a 
high affinity for oxygen even at low pressure. 
EXAMPLE 6 
Pillared cobalt complexes wherein R.sub.3 is a substituted N-succinimido 
were synthesized by initially synthesizing a precursor compound having the 
structural formula 
##STR10## 
by standard routes as described by P. J. McCarthy, et al. J. Am. Chem. 
Soc., 1955, 77, 5820. 
(a) SYNTHESIS OF Br.sub.2 ACACEN 
10 g of the above precursor compound was dissolved in 50 ml CHCl.sub.3, 10 
mg of benzoyl peroxide added, then 15.9 g of powdered N-bromosuccinimide 
added directly over 5 mins. A mild exotherm was observed and the solution 
became progressively cloudier. Stirring was continued at room temperature 
for 45 minutes followed by filtration which yielded a white solid. This 
was boiled in 800 ml. MeOH, concentrated by boiling to 400 ml then left to 
cool and crystallize. Filtration of first cooling yielded 8.0 g pure 
Br.sub.2 acacen. Reconcentration and cooling of liquors yielded a further 
1.4 g. Total yield=9.4 g. 
(b) SYNTHESIS OF A PILLARED COBALT COMPLEX wherein: R.sub.1 .dbd.R.sub.2 
.dbd.CH.sub.3 ; Y=(CH.sub.2).sub.2 ; R.sub.3 =phthalimido functionality 
0.485 g of potassium phthalimide and 0.5 g Br.sub.2 acacen were loaded into 
a 100 ml three-necked round bottom flask fitted with a condenser. Under a 
blanket of nitrogen, 50 ml dry DMF was added and the mixture refluxed for 
30 minutes. After cooling, a small amount of white solid was filtered off, 
the filtrate added to 500 ml H.sub.2 O and this mixture extracted with 
3.times.10 ml dichloromethane. The organic layer was then washed .times.3 
with H.sub.2 O and dried over anhydrous Na.sub.2 SO.sub.4. Evaporation 
yielded a yellow oil, plus some crystals which were filtered and 
recrystallized from 50/50 dichloromethane/methanol. Yield: 0.35 pure 
(phth).sub.2 acacen ligand (52% of theoretical). 
Under a blanket of nitrogen, 0.20 g (phth).sub.2 acacen was treated with 36 
mg of sodium metal predigested in 5 ml methanol. To this was added 86 mg 
CoBr.sub.2 in 5 ml MeOH and the mixture refluxed for 30 minutes. An 
initial yellow color was observed followed by the formation of an orange 
powder which was filtered off as the desired pillared cobalt complex. 
(c) USE OF THE COMPLEX TO BIND OXYGEN 
A solution of the above synthesized complex in either toluene +5% N-methyl 
imadazole or 1,2 dichloro ethane +5% pyridine was observed to reversibly 
bind O.sub.2 at room temperature. Exposure to air caused a rapid darkening 
in color. Application of vacuum or flushing with nitrogen restored the 
original color. 
EXAMPLE 7 
SYNTHESIS OF A PILLARED COBALT COMPLEX WHEREIN: 
##STR11## 
0.25 g of the Diels Alder adduct of maleimide and anthracene, prepared as 
taught by Ray, et al, JACS, 74, 1247 (1952) was mixed with 50 mg KOH in 10 
ml absolute ethanol and boiled for 10 minutes. This produced a white 
precipitate which was filtered, dried, then added to 10 ml DMF. 174 mg 
Br.sub.2 acacen and excess K.sub.2 CO.sub.3 were added and this mixture 
stirred 18 hours at room temperature. 500 ml H.sub.2 O were then added and 
the resultant suspension extracted .times.3 with 50 ml CHCl.sub.3. The 
organic layer was washed with H.sub.2 O and dried over anhydrous Na.sub.2 
SO.sub.4. Evaporation gave a yellow oil which was boiled in a minimum of 
50:50 methanol/dichloromethane to give a crystalline white material 
(.apprxeq.20 mg). 'HNMR spectroscopy indicated this to be substantially 
the free ligand of the desired cobalt complex. 
Under a blanket of nitrogen, this free ligand was dissolved in 100 ml 
MeOH/toluene 50:50 and shaken vigorously with excess CoBr.sub.2 +KOH for 
10 minutes. The organic layer was washed with H.sub.2 O to give a turbid 
orange solution. Drying over anhydrous NaSO.sub.4 overnight gave a 
transparent orange solution. Evaporation gave a yellowish solid. Addition 
of acetonitrile broke this up into a slurry of orange microcrystals of the 
Cobalt Complex having the above structure. 
Diacetamide or acetonitrile solutions of the above cobalt complex in the 
presence of a trace of pyridine, were observed to reversibly bind oxygen. 
Since maleimide is an excellent dienophile in Diels Alder reactions, it is 
capable of reacting with a wide range of diene-containing substances. The 
preparation of the above cobalt complex demonstrates that such Diels Alder 
adducts could be reacted with Br.sub.2 acacen to give a whole new series 
of pillared complexes. 
Having thus described the present invention, what is now deemed appropriate 
for Letters Patent is set out in the following appended claims.