Metallophthalocyanins and Benzoporphines
David Dolphin, Sams, J.R., and Tsin, T.
Inorganic Syntheses, D.H. Busch, Ed., John Wiley & Sons, New York, Vol. XX,
METALLOPHTHALOCYANINS AND BENZOPORPHINES 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 com pounds that frequently contain unusual structural features and unexpected stability. As an example, copper phthalocyanine can be heated in air to 550o for hours without decomposition, and it is unaffected by cold concentrated hydrochloric acid or molten sodium hydroxide. 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 states of coordinated metals, while the tetrabenzoporphyrins have properties more characteristic of porphines. Phthalocyanine itself is best prepared by self-condensation of phthalimidine, which is available from the reaction of phthalonitrile with ammonia. However, in many cases, direct metalation 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 metallated. The following procedures were reported:- A. [1,4,8,11,15,18,22,25-octamethyl-29H,31H- tetrabenzo[b,g,l,q] porphinato(2-)] cobalt(II) B. [ 1,4,8,11,15,18,22,25 octamethyl-29H,31H- tetrabenzo[b,g,l,q]porphine] C. Dilithium phthalocyanine D. [Phthalocyaninato(2-)] iron(Il)