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36. METALLOPHTHALOCYANINS AND BENZOPORPHINES
Submitted b y D. DOLPHIN,* J. R. SAMS * and T.
†
Checked by S. D. ITTEL and M. A. CUSHING, JR.†
B. TSIN*
The benzoporphines (I) and phthalocyanins (II) together constitute an unusual
class of organic ligands of exceptionally high thermal and chemical stability. As
with porphines, a large number of metals and nonmetals can replace the weakly
acidic hydrogen atoms at the center of the macrocyclic systems to form compounds that frequently contain unusual structural features and unexpected
o
stability. As an example, copper phthalocyanine can be heated in air to 550
*Department of Chemistry, The University of British Columbia, Vancouver, B .C. Canada
V6T 1W5.
†
Central Reserch and Development Department, Experimental Station, E . I. duPont de
Nemours and Co., Wilmington, DE 19898.
for hours without decomposition, and it is unaffected by cold concentrated
hydrochloric acid or molten sodium hydroxide.
1
The enormous amount of work on phthalocyanins reflects their prime importance to the dye and pigment industry and is attested to by the numerous
patents in the literature. It is our experience, however, that these materials are
rarely pure and that their purification, from unknown impurities, is invariably
more troublesome than performing the complete synthesis. Phthalocyanins are
stronger σ-donors than porphines, and the former stabilize higher oxidation
2
states of coordinated metals, while the tetrabenzoporphyrins have properties
more characteristic of porphines.
Phthalocyanine itself is best prepared3 by self-condensation of phthalimidine,
which is available from the reaction of phthalonitrile with ammonia. However,
in many cases, direct melaIation of the macrocycle cannot be achieved. Instead,
metalation by means of dilithium phthalocyanine or a template reaction,
whereby the macrocycle is formed around the metal using phthalonitrile (or one
of its derivatives), must be employed for the synthesis of metallophthalocyanins.
The tetrabenzoporphines can, like the phthalocyanins, be prepared by a
template reaction, or can, like the porphyrins, be directly metalated.
A.
[1,4,8,11,15,18,22,25-OCTAMETHYL-29H,31HTETRABENZ0[b,g l, q ] PORPHINATO(2-)] COBALT(II)
Procedure
The following reaction should be carried out under an atmosphere of nitrogen
to avoid slow air oxidation of the isoindole. Ammonium sulfate (350 g, 2.7
mole) and 2,5-hexanedione (180 g, 1.6 mole) are added to deoxygenated distilled water (3 L) in a 5-L round-bottomed flask and the solution is heated at
reflux under nitrogen for 24 hours. The red-brown solution is cooled to room
temperature and treated with 10% sodium hydroxide (about 300 mL) until it
is basic to litmus. At this stage, an off-white precipitate appears, and the mixture
is left to stand for several hours or overnight to complete precipitation of the
isoindole. The precipitate is collected by filtration, washed thoroughly with
water, and dried under vacuum for 24 hours to give 75 g of crude 1,3,4,7tetramethylisoindole (III).
The crude isoindole is dissolved in diethyl ether (2 L) under nitrogen. The
solution is filtered and reduced in volume to 300 mL. It is then left under
nitrogen for several hours until crystallization is complete. The fluffy white
precipitate is collected by filtration, washed with a Uttle diethyl ether, and dried
2
under vacuum to give pure 1,3,4,7-tetramethylisoindole (mp, 144° in vacuo).
Yield: 60 g (33%). This product is used for the preparation of metaUoporphines.
(Pink coloration due to isoindole oxidation does not reduce yields in subsequent
steps).
■ Caution. The Carius tube will explode if the reaction is scaled up or the
tube size is reduced at this point. Face shield and heavy gloves should be worn
when handling the tube after reaction. The tube should be cooled to -198°
before opening.
1,3,4,7-Tetramethylisoindole (6 g, 34.6 mmole) and cobalt powder (30 g,
0.51 mole) are mixed and loaded into a Carius tube (4 X 35 cm; volume about
450 mL). After it is evacuated and sealed, the tube is placed in a shielded oven
preheated to 390° and heated at this temperature for 4 hours. After the tube is
cooled, the dark-blue (or black) powder is placed in a Soxhlet extractor and
extracted with pentane (300 mL) until a red-brown impurity is removed (about
24 hours). The pentane is replaced by toluene (300 mL), and extraction is
continued until the extract (initially green) is colorless (about 8 hr). Finally,
pyridine (300 mL) is used to extract (Soxhlet extractor) the porphine, which
requires about 10 hours. The pyridine solution is concentrated to 20 mL, and
IOOmL of hexane is added. The precipitate is collected, washed with hexane, and
dried overnight in vacuum at 60°, to give [octamethyltetrabenzoporphinato(2-)]cobalt(II). Yield: 2-3 g (35-55%). Anal. Calcd. for C44H36N4Co: C, 77.79;
H, 5.30; N, 8.24. Found: C, 77.87; H, 5.40;N, 8.48.
Properties
[Octamethyltetrabenzoporphinato(2-)]cobalt(II) is a green-blue powder that is
stable towards atmospheric oxidation in the solid state. The compound is readily
soluble in pyridine bases and tetrahydrofuran, and to a lesser extent in diethyl
ether, benzene, ethanol, and acetone. The electronic spectrum in pyridine shows
bands at 320 (e = 13,200), 455 (e = 71,500), and 645 nm (e = 36,700).
B. [ 1,4,8,11,15,18,22,25 OCTAMETHYL-29H,31HTETRABENZO[b,g,l,q]PORPHINE]4
J
Procedure
1,3,4,7-Tetramethylisoindole (III) (6 g, 34.6 mmole) (see above) and magnesium
powder (8 g, 0.33 mole) are allowed to react, in the manner described above for
the cobalt complex, to give [octamethyltetrabenzoporphinato(2-)] bis (pyridine)magnesium. Yield: 4.6 g (67%). The magnesium complex (0.3 g, 0.37 mmole)
is dissolved in trifluoracetic acid (25 mL), and the solution is stirred for 2 hours.
The green solution is filtered and water is slowly added until a dark-blue precipitate is formed.This precipitate is collected by filtration, washed with water, and
dried in high vacuum for 6 hours. The dark-blue material, which may still contain some unreacted magnesium octamethyltetrabenzoporphine, is suspended in
boiling pyridine (100 mL) for 5 minutes. After it is cooled to room temperature,
the mixture is filtered and the filtrate is discarded. The residue is again suspended in hot pyridine and the process is repeated until the filtrate is colorless.
The solid is then dissolved in boiling quinoline (100 mL) and is filtered hot; the
filtrate is set aside to crystallize overnight. The product is collected by filtration
and dried in vacuum at 150°. Yield: 0.25 g (83%).Anal. Calcd. TorC44H38N4:
C, 84.85; H, 6.15; N, 9.00. Found: C, 84.55; H, 6.18; N, 8.73.
Properties
Octamethyltetrabenzoporplune is a dark-blue powder that, although much more
soluble than tetrabenzoporphine, has a low solubility in most common organic
solvents. It is, however, very soluble in trifluoroacetic acid, giving a green solution of the diprotonated macrocycle. This molecule is a square-planar letradentate ligand. It reacts with a variety of metal salts to form porphine-metal
complexes. In general such metalations are best carried out in quinoline. The
electronic spectrum contains the following bands: 415 (e = 75,000), 440 (e =
280,000), 530 (e = 10,000), 630 (e = 7,500), 690 nm (e = 80,000).
C DILITHIUM PHTHALOCYANINE5
Procedure
Clean lithium metal (0.2 g, 29 mmole) is placed in reagent grade pentyl alcohol
(30 mL) in a 50-mL, round-bottomed flask fitted with a reflux condenser and
Drierite tube (the reactants and products are sensitive to moisture in all subsequent operations), and the mixture is warmed to dissolve the lithium. Phthalonitrile (3 g, 18.3 mmole) is then added to the mixture, which initially turns
yellow, then rapidly dark blue. The mixture is heated at reflux for 0.5 hour,
taking care for the first 5 minutes against too vigorous a reaction and foaming.
The solvent is removed on a rotary evaporator using a vacuum pump rather than
a water aspirator. The oily residue is heated at 250° under vacuum to produce
a green powder, which is placed in a Soxhlet extractor and extracted with
freshly distilled acetone (200 mL) (reagent grade acetone is heated at reflux for
13 hr over CaSO4 before distillation). When all the blue pigment has been extracted (usually 8 hr), the acetone is reduced in volume to 20 mL. Hexane
(100 mL) is added and the mixture is left to stand overnight. The solvated
product is collected by filtration and heated under vacuum at 250° for 3 hours
to give the blue dilithium phthalocyanine 2.3 g (75%).
A portion of the product (0.5 g, 0.95 mmole) is dissolved in freshly distilled
dry acetone (100 mL) and the solution is filtered. The filtrate is reduced in volume to about 10 mL, dry toluene/hexane,49:1 (50 mL) is added, and the mixture is allowed to stand overnight to give crystals of the solvated product, which,
after filtration and washing with a little toluene/hexane (49:1), are heated under
vacuum at 250° for 2 hours to give pure dilithium phthalocyanine, 0.45 g (90%).
Anal. Calcd. for C32H16N4Li2: C, 73.0; H, 3.04; N, 21.30. Found: C, 72.8;
H,3.08;N, 21.10.
Properties
Dilithium phthalocyanine is obtained as dark-blue crystals. The compound has
high thermal stability, as is typical of many phthalocyanins. It is soluble in
acetone, giving a deep-blue solution that deposits phthalocyanine when in contact with even trace amounts of water. The material is also soluble in ethanol
and tetrahydrofuran, but it is insoluble in diethyl ether, hexane, or chloroform.
Solutions of the dilithium complex in ethanol react rapidly and quantitatively
with a variety of metal salts to give the metallophthalocyanines, which precipitate, in very pure form, from solution. The electronic spectrum contains the
bands (acetone solution): 370 (e = 24,800), 596 (e = 17,300), 630 (e = 16,100),
655 n m ( e = 11,100).
D. [PHTHALOCYANINATO(2-)] IRON (Il)6
Procedure
Phthalonitrile (2.9 g, 17.7 mmole) and iron powder 5 g, 0.09 mole) are intimately mixed and placed in a 25-mL conical flask. The mixture is heated in a
Wood's metal or sand bath at 260° for 5 hours. Phthalonitrile that condenses
on the cooler upper portion of the flask should be scraped down to the bottom
periodically. The blue product is finely ground and extracted in a Soxlilet
extractor with ethanol (200 mL) for 5 hours. The ethanol is replaced by pyridine (200 mL), and the extraction is continued for a further 5 hours. The
pyridine extract is reduced in volume to 20 mL, and hexane is added to precipitate the blue [phthalocyaninato(2-)] bis(pyridine)iron(II), which is collected by
filtration, washed with ethanol, and dried in vacuum to give 0.8 g of Fe(pc)py2
(pc = phthalocyanine, py = pyridine). A portion (0.1 g) of tills material can be
further purified by dissolving in pyridine (30 mL) and filtering the solution by
suction through alumina (3 X 10 cm Woelm alumina grade I). Hexane (100 mL)
is added to the filtrate and the blue precipitate is collected by filtration, washed
with petroleum ether, and sublimed in vacuum at 300° to give the dark-blue
[phthalocyaninato(2-)]iron(II). Yield: 0.05 g (50%). Anal. Calcd. for C32H16N8Fe: C, 67.5;H, 2.8;N, 19.7. Found: C, 67.1;H, 2.8;N, 19.7.
Properties
[Phthalocyaninato(2-)] iron(II) is a dark blue, thermally stable solid that can be
sublimed in vacuo a t 300°. It is very soluble in pyridine, giving deep blue solutions of the bis(pyridine) adducts. It also forms an unstable purple hexaaniline
adduct when dissolved in aniline. It is soluble in concentrated sulfuric acid and
dimethyl sulfoxide (slightly) but is insoluble in most other organic solvents. The
iron (II) complex, unlike the corresponding iron (II) porphines, is relatively
stable toward oxidation to the iron (III) state. The electronic spectrum shows the
following absorption bands: (1-chloronaphthalene solution) 595 (e = 16,000),
630 (e « 17,000), 658 (e = 63,000); (pyridine solution) 333 (e = 45,000), 415
(e = 15,000), 395 (e = 2000), 658 nm (e = 8000).
References
1.
2.
3.
4.
5.
6.
A. H. Jackson, Azaporphyrins, Vol. I of The Porphyrins, D. Dolphin, Ed., Academic,
New York, 1978.
C O. Bender and R. Bonnett,/. Chem. Soc (C), 1968, 3036.
P. J. Brach, S. J. Grammatica, O. A. Ossanna, and L. Weinberger, /. Heterocyclic Chem.,
7, 1403 (1970).
C. O. Bender, R. Bonnett, and R. G. Smith,/. Chem. Soc (C), 1970, 1251.
P. A. Barrett, D. A. P'rye, and R. P. Linstead,/. Chem. Soc., 1938, 1157.
R. P. Linstead,/. Chem. Soc., 1934, 1016.