Angen Chem. Inr Ed. Engl. 25 (1986) No. 3 0 VCH Verlagsgesellschafi mbH. 0-6940 Wernheim, I986 0570-0833/86/0303-0259 $ 02 50/0

Dtw'ilctrtecl to Piofcrc.or Eimt Otto F i~t h e r 017 the> ol c ci\ioi? of h r~ 75th birt~7da1The coordination chemistry of metals in unusual oxidation states is a fascinating aspect of research in the field ofmetalloporphyrins. Of particular significance in this respect are oxoiron porphyrins containing tetravalent iron, since complexes of this sort occur as reactive intermediates in numerous biological and biomimetic oxidation processes."] Iron(iv) porphyrins, in which the metal is not present as part of a [Fe=O] (FRG) phyrinoids corrole["-the aromatic parent substance of corrin. the ring system of vitamin B,, --and iso~orrole['~ may enable the preparation of the corresponding neutral complexes, that is. types 2 and 4, respectively. This supposition appeared to be substantiated all the more so. as it was recently shown that stable iron(iv) complexes with ligands based on pentane-2,4-dione-bis(S-alky1isothiosemicarbazides)-which are also trianionic-could be synthesized.18,9] We have now found that octaethylcorrole 5 can be readily converted into the triad of stable complexes 7-9, all of which contain formally tetravalent iron."'] Furthermore, the existence of the iron corrole 10 (bearing an axial pyridine ligand) with a formal oxidation state of the metal of + 111 was corroborated.

Until very recently the Ni and Cu corroles, already described in the sixties, were regarded as the MII complexes 1 (M = Ni, Cu). Some doubt arose about this interpretation after the existence of FeIV corroles demonstrated that corroles can stabilize metals in unusual oxidation states. Thorough physical studies have now shown that the metal atoms in the Ni and Cu corroles do in fact have the formal oxidation state +III (2).

Angew. Chem. lnt. Ed. Engl. 26 (1987) No. 9 Angen Chem. I n f . Ed. Engl. 26 (1987) No. 9 0 VCH Verlagsgesellschafi mbH. 0-6940 Weinheim. 1987 0570-0833/87/0909-0931 $ 02.50/0

The electrochemistry and spectroscopic properties of three iron corroles were examined in benzonitrile, dichloromethane, and pyridine containing 0.1 M tetra-n-butylammonium perchlorate or tetra-n-ethylammonium hexafluorophosphate as supporting electrolyte. The investigated compounds are represented as (OEC)Fe(IV)(C(6)H(5)), (OEC)Fe(IV)Cl, and (OEC)Fe(III)(py), where OEC is the trianion of 2,3,7,8,12,13,17,18-octaethylcorrole. Each iron(IV) corrole undergoes two one-electron reductions and two or three one-electron oxidations depending upon the solvent. Under the same solution conditions, the iron(III) corrole undergoes a single one-electron reduction and one or two one-electron oxidations. Each singly oxidized and singly reduced product was characterized by UV-vis and/or EPR spectroscopy. The data indicate a conversion of (OEC)Fe(IV)(C(6)H(5)) and (OEC)Fe(IV)Cl to their iron(III) forms upon a one-electron reduction and to iron(IV) corrole pi cation radicals upon a one-electron oxidation. The metal center in [(OEC)Fe(III)(C(6)H(5))](-) is low spin (S = (1)/(2)) as compared to electrogenerated [(OEC)Fe(III)Cl](-), which contains an intermediate-spin (S = (3)/(2)) iron(III). (OEC)Fe(III)(py) also contains an intermediate-spin-state iron(III) and, unlike previously characterized (OEC)Fe(III)(NO), is converted to an iron(IV) corrole upon oxidation rather than to an iron(III) pi cation radical. Singly oxidized [(OEC)Fe(IV)(C(6)H(5))](*)(+) is the first iron(IV) tetrapyrrole pi cation radical to be isolated and was structurally characterized as a perchlorate salt. It crystallizes in the triclinic space group P&onemacr; with a = 10.783(3) Å, b = 13.826(3) Å, c = 14.151(3) Å, alpha = 78.95(2) degrees, beta = 89.59(2) degrees, and gamma = 72.98(2) degrees at 293 K with Z = 2. Refinement of 8400 reflections and 670 parameters against F(o)(2) yields R1 = 0.0864 and wR2 = 0.2293. The complex contains a five-coordinated iron with average Fe-N bond lengths of 1.871(3) Å. The formulation of the electron distribution in this compound was confirmed by Mössbauer, X-ray crystallographic, and magnetic susceptibility data as well as by EPR spectroscopy, which gives evidence for strong antiferromagnetic coupling between the iron(IV) center and the singly oxidized corrole macrocycle.

The synthesis, electrochemistry, spectroscopy, and structural characterization of two high-valent phenyl sigma-bonded cobalt corroles containing a central cobalt ion in formal +IV and +V oxidation states is presented. The characterized compounds are represented as phenyl sigma-bonded cobalt corroles, (OEC)Co(C(6)H(5)) and [(OEC)Co(C(6)H(5))]ClO(4), where OEC is the trianion of 2,3,7,8,12,13,17,18-octaethylcorrole. The electronic distribution in both molecules is discussed in terms of their NMR and EPR spectroscopic data, magnetic susceptibility, and electrochemistry.

COMMUNICATIONS [7] Crystal structure analyses. colorless crystals of 3a and 15 were investieated on a lour-circle diffractometcr (CAD4, at -80 'c' with Cu,, radiation ( 2 =154.178 pm). 3a: C,,H,,B,Li,SiZ.2THF. crystal dimensions 0 6 x 0.3 x 0.2 inm'. monoclinic. space group P2,c. Z = 4. (I = 9 7 2 3 2 ) . h = 1173.5(2). <' = 2890.7(6) pm. / I = 98.45(3) . Vr7 = 3262.1 x lO-"m', pca,Ld = 0.99X gcm -'; 3994 measured reflections in the range up to 20 = 110 (w scans). 3903 of which \+ere independent and were used for the further calculati~ns alter Loreiitz and polarization correction: no absorpt~on correction 111 = I 1 Ocm-') The structure was solved by direct methods and refined against the ti: data xith full matrix. A disorder showing up in the differenceFourlei-5yntheses was accounted for bq a "split atom model" where a C 5 -SiMe, group superposes the B3-iBu unit at 8 3 and. vice versa. a B3-/Bu group superposes the C5-SiMe3 unit at C 5 . Due to these superpositions. geometrrc restraints olihe B C (160 pm) and Si-C (187 pm) bond length wcrc used during refinement. and the temperature factors of atoms approaching each other were defined to be equal. In this way good conbergence and a maximal residual electron density 0.35 e k ' were achieved. The distribution of the alternative arrangements of the molecules was determincd to be 59.3(4) aiid 40.7%). The H a t o m u'ere localized iii part by dillerence Fourier syntheses: the others were calculated; they were included in the calculation riding on their bonding partners and with isotropic temperature factors coinmon by gsoups. Anisotropic teinpcratui-e factors %ese used foi-all the remaining atom& except C 7 . wRi = 0.2066 (SHELX 93 program). corresponding to R = 0.069 for 2951 reflections with &>4u(F,>). inanimal residual electron density 0.33 e k ' . -15: C,,H,,B,Si,, crystal dimcnsions 0.7 x 0.3 x 0.2 n1m3, monoclinic. space group P2,:n. Z = 4. ci = 928.9(2). h = 1655,2(3). c = 2154.4(4) pin. /) = 92.80(3) , VF7 = 3308.5 x I O -" in'. pc,,L6 = 1.009 gcni-'; 4461 reflections iii the range up to 211 =110 ( ( , I scans), 4157 of wliicli were independent 41 54 reflections \+ere used foi-further calculations after Lorentr aiid polarizatioii correction. the structure solutioii and refinement a s for 3 a led to wR,=0.1955, corresponding to R = 0.064 for 2123 reflections uith ti) > 40(&,). and ;I maximal residual electron densit) of 0 34 e k ' . Further details of the crystal structure investigations inay be obtained from the Fachiiiformationsreiitrum Karlsruhe. D-76344 Eegenstein-Leopoldslitifeii (FRG). on quoting the depository number CSD-58435.

No abstract