Free Phthalocyanines

Metal phthalocyanines may also be prepared using alkaU metal salts or from metal-free phthalocyanine by boiling the latter in quinoline with metal... 

Some references cover direct preparation of the different crystal modifications of phthalocyanines in pigment form from both the nitrile—urea and phthahc anhydride—urea process (79—85). Metal-free phthalocyanine can be manufactured by reaction of o-phthalodinitrile with sodium amylate and alcoholysis of the resulting disodium phthalocyanine (1). The phthahc anhydride—urea process can also be used (86,87). Other sodium compounds or an electrochemical process have been described (88). Production of the different crystal modifications has also been discussed (88—93). 

However, they can also be prepared by metal exchange from alkali-metal phthalocyanines. If proton donors like hydrochloric acid, water or methanol are added to the reaction mixture of a freshly prepared alkali-metal phthalocyanine, metal-free phthalocyanines (PcH2) are formed (see Section 2.1.4.1,). If, on the other hand, the appropriate metal salt is added to a solution of an alkali-metal phthalocyanine, the product is the metalated compound (PcM) (see Section 2.1.6.). 

Especially in the case of metal-free phthalocyanines, a template effect cannot be involved and the reaction has to pass via intermediates 4, 5 and 6 which have been isolated6,87,88 or like 7 which has only been postulated.89... 

Usually metal-free phthalocyanine (PcH2) can be prepared from phthalonitrile with or without a solvent. Hydrogen-donor solvents such as pentan-l-ol and 2-(dimethylamino)ethanol are most often used for the preparation.113,127 128 To increase the yield of the product, some basic catalyst can be added (e.g., DBU, anhyd NH3). When lithium or sodium alkoxides are used as a base the reaction leads to the respective alkali-metal phthalocyanine, which can easily be converted into the free base by treatment with acid and water.129 The solvent-free preparation is carried out in a melt of the phthalonitrile and the reductive agent hydroquinone at ca. 200 C.130 Besides these and various other conventional chemical synthetic methods, PcH2 can also be prepared electrochemically.79... 

Aluminum phthalocyanine (PcAlX) can be prepared from the phthalonitrile and aluminum trichloride either in refluxing quinoline138 13g or without a solvent under addition of ammonium molybdate(VI).137 The chloro compound can be transformed to a hydroxy derivative by treatment with sulfuric acid.58-140 Also, the insertion of aluminum in a metal-free phthalocyanine is possible, for example trialkylaluminum can be used.141,142... 

Tin phthalocyanines can be prepared using tin(II)110 or -(IV)154 chlorides. The reaction can be performed in 1-chloro-1 10,1 37,1 55 or 1-bromonaphthalene,154 starting from phthalonitrile110137154,155 or phthalic anhydride. In the second case, urea and ammonium molyb-date(VI) arc added.137 The central tin atom can also be introduced into metal-free phthalocyanine by the reaction with tin(IV) chloride in dimethylformamide.141 Treatment of PcSnCl2 with disodium phthalocyanine in refluxing 1-chloronaphthalenc forms a sandwich-like bis-(phthalocyanine) Pc2Sn.154... 

Antimony phthalocyanine can be prepared in a melt of antimony(III) chloride and phthalonitrile. The obtained product is of the formula [PcSb(Cl)2] SbClfi.164 PcSbX is formed by the reaction of metal-free phthalocyanine with antimony(III) chloride in l-chloronaphthalene59 or by the reaction of metal-free phthalocyanine with antimony(III) fluoride.165... 

Palladiumphthalocyanine (PcPd) can be synthesized from phthalimide, ammonium molyb-date(VI), urea and palladium(II) chloride in nitrobenzene.285 Peripherally substituted palladium phthalocyanine is prepared by the reaction of phthalonitrile286 or isoindolinediimine114,117 and palladium(II) acetate in 2-(dimethylamino)ethanol. Also a metal insertion into metal-free phthalocyanine in dimethylfonnamide starting from bis(triphenylphos-phane)palladium(II) chloride has been performed.141,287... 

Due to its commercial importance, the synthesis of copper phthalocyanine (PcCu) is the best investigated of all the phthalocyanines. Copper phthalocyanine is prepared from phthalonitrile and copper(I) chloride without solvent137 and also in a melt of urea.229,277 Additionally, the insertion of copper into metal-free phthalocyanine in butan-l-ol and pentan-l-ol is possible. The copper salts used in this case are copper(I) chloride112 and copper(II) acetate.290 Starting from copper(II) acetate, copper phthalocyanine can also be prepared in ethylene glycol.127 As mentioned above, copper phthalocyanine often occurs as a byproduct of the Rosenmund-von Braun reaction. To increase the yield of the phthalocyanine the solvent dimethylformamide can be substituted by quinoline. Due to the higher boiling point of quinoline, the copper phthalocyanine is the main product of the reaction of copper(I) cyanide and 1,2-dibromoben-zene.130... 

The preparation of silver phthalocyanine (PcAg) is carried out by metal insertion into metal-free phthalocyanine from silver(I) nitrate. The reaction is performed in dimethylformamide291 or in a mixture of 1,2-dichloroethane, sodium acetate and acetic acid.231... 

Zinc phthalocyanine (PcZn) is prepared from phthalonitrile in solvents with a boiling point higher than 200 C, e.g. quinoline277,278 or 1-bromonaphthalene,137 or without solvent in a melt of phthalonitrile.83,116 The zinc compound normally used is zinc(ll) acetate or zinc powder. The reaction of zinc(II) acetate with phthalic acid anhydride, urea and ammonium mo-lybdate(VI) is also successful.262 The metal insertion into a metal-free phthalocyanine is carried out in an alcohol (e.g.. butan-l-ol).127,141,290 This reaction can be catalyzed by an alkali metal alkoxide.112,129... 

Yields not reported. h The central metal-free phthalocyanine was formed. 

The products are known as 2,3-octasubstituted or 2,3,9,10,16.17,23,24-octasubstituted phthalocyanines. As is the case for 1,4-octasubstituted phthalocyanines, only one structural isomer exists. Metal-free phthalocyanines 18 can be obtained by heating 4,5-disubstituted phthalonitriles 17 in a solvent containing a strong base such as l,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Ammonia can also be used as a base. 

Ring enlargement from subphthalocyanines has been used to synthesize unsymmetrically substituted metal-free phthalocyanines of the AAAB type (see p 738). 

A mixture of metal-free phthalocyanine PcH2 (0.3 g, 0.6 mmol), anhyd DMSO (40mL) and a solution of BuLi (0.075 g, 1.2 mmol) was heated to reflux and kept at this temperature until no more bubbles of butane came o(T. To the resulting solution of the phthalocyanine dianion I successive additions were made of solutions of Ca(OAc)2 (0.1 g, 0.6 mmol) in DMSO (2 mL)and of Lu(OAc)3 (0.5 g, 1.4 mmol) in DMSO (3 mL). The mixture was refluxed for about 1 min, cooled, and diluted with twice the volume of H,0. The precipitate formed was filtered, carefully washed with H20, and dried at 150 C/5 Torr lo give the title compound yield 0.4g (92%). 

The exchange of lithium in a dililhium phthalocyanine is a useful tool to prepare metal (e.g., zinc) or metal-free phthalocyanines. For this purpose, the dilithium phthalocyanine is prepared by reaction of phthalonitrile and lithium alkoxide in an alcohol, e.g. pentan-l-ol. In most cases, the lithium phthalocyanine is not separated but directly converted into the respective phthalocyanine by treatment with metal salts or, in the case of metal-free phthalocyanine, with acid or water. 

Metal-free phthalocyanines can also be transferred into the metal phthalocyanines (e.g., PcCu, PcZn, PcNi) by treatment with the respective metal acetates in penlan-l-ol.290... 

Dilithium phthalocyanines are readily converted to metal-free phthalocyanines on hydrolysis. To prepare 1,8,15,22-tetrasubstituted phthalocyanines 4 the corresponding 3-monosubstituted phthalonitriles 3 have to be used. 

Phthalocyanines 2 can be made from metal-free phthalocyanines 1 by hydrogen/metal exchange. 

Similarly, a nickel(II) 2,3,9,10,16,17,23,24-octacyanophthalocyanine can be produced in 86% yield from the corresponding metal-free phthalocyanine and nickel(I I) acetate in dimethylform-amidc at 100 C for two hours.427... 

If lanthanide salts (e.g., Yb(OAc)3 H20) are used as the metal compound, hexadecasub-stituted bis(phthalocyanines) can be prepared starting from 2,3,9,10,16.17,23,24-octa-substituted metal-free phthalocyanines.201... 

Similarly, metals may be introduced into un symmetrically substituted metal-free phthalocyanines, e.g. formation of the zinc coordination compound 6.419... 

Hexacoordinated phosphorus compounds derived from phthalocyanines have been similarly prepared. Hanack investigated the reaction of metal-free phthalocyanines with POBr3 or POCI3 in presence of pyridine [98]. The corresponding dihydroxyphosphorus phthalocyanine hydroxides 60 were characterized. 

Organic dyes, aside from their role as sensitization agents for wide band gap semiconductors have been employed also for stabilization of narrow band gap semiconductors. The majority of such studies have considered metal or metal-free phthalocyanine films for both sensitization and electrode protection purposes [35]. 

A novel tetraazaporphyrinato (TAP) and phthalocyaninato mixed het-eroleptic rare-earth compound, LnPc (TAP) with photochromic and electrochromic features has been readily synthesized by a one-pot reaction using Eu(acac)3-wH20, metal-free phthalocyanine H2Pc (Pc = 2,3,9,10,16,17,23,24-octakis(decyloxy)phthalo-... 

---