5702 J. Am. Chem. zyxwvut SOC. zyxwvu 1994,116, 5702-5713 Oxidation of Metal-meso-Octaethylporphyrinogen Complexes Leading to Novel Oxidized Forms of Porphyrinogen Other than Porphyrins. 2. The Redox Chemistry of Iron(I1)- and Cobalt( 11)-meso-Oct aethylporphyrinogen Complexes Occurring with the Formation and Cleavage of Two Cyclopropane Units Stefania De Angelis,? Euro Solan,? Carlo Flonani,'J Angiola Chiesi-Villa,*and Corrado Rizzoli* Contributionfrom the Institut de Chimie Miniale et Analytique, Universitb de Lausanne, Place du Chateau 3, zyxwvut CH-1005 Lausanne. Switzerland, and Istituto di Strutturistica Chimica, Centro di Studio per la Strutturistica Diffrattometrica del CNR, Universitb di Parma. I-43100 Parma. Italy Received January 20, 1994' Abstract: In this paper we report a four-electron oxidation of a porphyrinogen tetraanion leading to a neutral form containing two cyclopropane units complexes to iron(II), iron(III), and cobalt(I1). The redox chemistry of the meso- zy octaethylporphyrinogen+xbalt(II) complex clarified the stepwiseprocess leading to the oxidized forms of porphyrinogen. The reaction of the iron(I1)-meso-octaethylporphyrinogen complex [EtsNdFeLiz(THF)4] (1) with CuClz led to a four-electronoxidation of the porphyrinogen skeleton and the formation of two cyclopropane units. Such an oxidation converts the meso-octaethylporphyrinogen tetraanion into a neutral ligand which is bonded via the nitrogen atoms to the [FeCl]+ cation and with a C = C double bond of each pyrrole to the four copper(1) atoms of the [Cu4Cls]- cluster in [E~~N~(A)~F~CI.-~C~~CII] (2). Thestabilization of the four-electronoxidized form is independentof interaction with the [Cu4Cls]- cluster, as proven by the isolation of a copper free form. The oxidation of [E~sN,]-[L~(THF)~]+ (3) with CuC12 under different conditions led to the porphyrinogen-bis(cyc1opropane) form binding exclusively iron(II1) in [Et8N4(A)2FeC1]2+[FeC14]2- (4) [(A) zyxwvuts = abbreviation for cyclopropane]. The structure of 4 has been established by an X-ray analysis. A comparison between the structures of 1 and 4 singles out the conformational changes occurring on the porphyrinogen skeleton upon a four-electron oxidation and formation of two cyclopropane units. The stepwise nature of such an oxidation has been clarified by studying the oxidation of [EtsN.&oLiz(THF)4] (5), which can be converted by reaction with 1 mol of CuClz to the corresponding cobalt(II1) derivative ( [Et8N4Co]-[Li(THF)#] (6) and undergoes a further oxidation by CuC12 to [Et8N4(A)Co] (7), containing the oxidized form of porphyrinogen with a cyclopropane unit. An intermolecular redox process, dependent on the nature of the solvent, occurs between 7 and 5, leading to the formation of 6. In the presence of coordinating solvents, 6 is the stable form, while in hydrocarbons, it disproportionates into 5 and 7. The best synthesis of 7 is achieved by the oxidation of 5 with an excess of p-benzoquinone. The cyclopropaneunit can be reduced by twoelectrons by reacting 7 with excesslithiummetalor by reductivedemetalation with HzS. The reaction of 7 with CuClz leads to a further oxidation of porphyrinogen by two electronsand the formation of a second cyclopropane unit. The fully oxidized form of porphyrinogen is a neutral ligand. Complex 8, [(EtsN4(A)2- CoCl}-.(Cu4CIs~], has been structurally characterized and like 2 contains the oxidized form bonded to [CoCl]+ via nitrogen atoms and to the [CU~CISI- cluster via the pyrrolic C = C bonds. Crystallographic details: 1 is monoclinic, space group C2/c, a = 20.749(2) A, b = 10.930(1) A, c = 22.797(2) A, a = y = 90°, @ = 104.69(2)O, Z = 4, and R = 0.044. 4 is orthorhombic, space group Pbca, a = 23.144(4) A, b = 30.264(7) A, c = 13.362(3) A, a = @ = y = 90°, Z = 8, and R = 0.053. 7 is monoclinic, space group P2,, a = 15.804(2) A, b = 12.237(1) A, c = 17.026(3) A, a = y = 90°, @ = 91.15(2)', 2 = 4, and R = 0.069. 8 is triclinic, space group Pi', a = 15.361(3) A, b = 15.548(4) A, c = 12.060(5) A, a = 107.66(2)', /I = 99.62(2)', y = 86.30(2)', Z = 2, and R = 0.080. Introduction Although meso-octaalkylporphyrinogens, a class of molecules whose prototype was discovered by Baeyer in 1886,' have some unique chemical and topological properties, they have not received much attention.2 One of the most interesting aspects of meso- * To whom correspondence should be addressed. t Universitt de Lausanne. t'Universit8 di Parma. (1) Baeyer, A. Chem. Ber. 1886,19,2184. (2) (a) Fischer, H.; Orth, H. Die Chemie des Pyrrols; Akademische Verlagsgesellschaft; Leipzig, Germany, 1934; p 20. (b) Dennstedt, M.; Zimmermann, J. Chem. Ber. 1887, 20, 850, 2449; 1888, 21, 1478. (c) Dennstedt, D. Chem. Ber. 1890,23,1370. (d) Chelintzev, V. V.; Tronov, B. V. J. Russ. Phys.-Chem. Soc. 1916, 48, 105, 127. (e) Sabalitschka, Th.; Haase, H.; Arch. Pharm. 1928, 226. 484. zyxwvutsrqp (0 Rothcmund, P.; Gage, C. L. J. Am. Chem. SOC. 1955, 77, 3340. Abstract published in Advance ACS Abstracts, June 1, 1994. OOO2-7863/94/1516-5702$04.50/0 octaalkylporphyrinogen chemistry is related to its use as a ligand for transition metals, a field entered by this groupin recent years." The tetraanion generated by reaction of the meso-octaethyl derivative EtsN4H43 with BunLi gave rise to a starting material, [ E~EN~L~~(THF)~],~ which allowed entry into organometallic and coordination chemistry in nonaqueous solutions. (3) Jacoby, D.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Chem. Soc., (4) Jacoby, D.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Chem. Soc., (5) Jacoby, D.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Am. Chem. Chem. Commun. 1991,220. Chem. Commun. 1991,790. Soc. 1993. 115. 3595. ~ (6) Jubb, J.f Jacoby, D.; Floriani, C.; Chiesi-Villa, A.; Riuoli, C. Inorg. Chem. 1992.31, 1306. (7) Jacoby, D.; Floriani, C.; Chiesi-Villa, A,; Rizzoli, C. J. Am. Chem. Soc. 1993,IlS,7025. (8) Juhb, J.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J. Am. Chem. Soc. 1992,114, 6571. 0 1994 American Chemical Society