Tetracoordinated Manganese(III) Alkylcorrolates. Spectroscopic Studies and the Crystal and Molecular Structure of (7,13-Dimethyl-2,3,8,12,17,18-hexaethylcorrolato)manganese(III) Silvia Licoccia,* ,² Elisabetta Morgante, ² Roberto Paolesse, ² Francesca Polizio, ‡ Mathias O. Senge, § Eugenio Tondello, | and Tristano Boschi ² Dipartimento di Scienze e Tecnologie Chimiche and Dipartimento di Biologia, Universita ` di Roma Tor Vergata, Via della Ricerca Scientifica, 00133 Rome, Italy, Institut fu ¨r Organische Chemie (WE02), Freie Universita ¨t, Takustrasse 3, D-14195 Berlin, Germany, and Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, Universita ` di Padova, Via Loredan 4, 35131 Padua, Italy ReceiVed March 28, 1996 X (2,3,7,8,12,13,17,18-Octamethylcorrolato)manganese(III), [Mn(OMC)], has been characterized by several physical measurements. In the presence of nitrogenous bases the complex exists as a valence tautomer [Mn II (OMC •+ )] as demonstrated by 1 H NMR and EPR. Complete resonance assignment in the NMR spectrum has been achieved by systematic substitution of the peripheral substituents. The crystal structure of the first example of a tetracoordinated tetrapyrrolic macrocycle Mn(III) complex, (7,13-dimethyl-2,3,8,12,17,18-hexamethylcorrolato)- manganese(III), [Mn-7,13-Me 2 -HEC)], is also reported. Crystal data with Cu KR (λ ) 1.541 78 Å) at 293 K are as follows: C 33 H 39 MnN 4 , a ) 4.671(2) Å, b ) 28.31(2) Å, c ) 20.882(6) Å,  ) 94.60(3)°, V ) 2753(2) Å 3 , Z ) 4, monoclinic, space group P2 1 /n, 4088 data, R1 ) 0.0563 for 4088 observed reflections with I > 2σ(I). The analysis reveals a high degree of planarity of the macrocycle and the existence of strong overlap between the π systems with the formation of an infinite stack of molecules. Introduction Among the various tetrapyrrolic macrocycles corrole is a particularly interesting one because of its structure that can be considered as intermediate between that of the porphyrin, the prosthetic group of hemoproteins, and that of corrin, the nucleus of vitamin B 12 coenzyme. It has, in fact, a corrin-like molecular skeleton, with a direct link between two pyrrole rings and a porphyrin-like 18 electron π system. Corrole is then aromatic as confirmed by its electronic and NMR spectra. It is a very versatile ligand capable of coordinating several main group and transition metals. Synthetic and spectroscopic studies carried out on metal derivatives of corrole have shown that its ligand field substantially differs from that of other macrocycles. 1 To gain a better understanding of the metal-macrocycle bond we have now extended our investigations to manganese corro- lates. Manganese is present in numerous biological systems: by variation of its oxidation and ligation states it mediates several biological functions. 2,3 Furthermore manganese complexes have been successfully used as catalysts for the mild homogeneous oxidations of different organic functions. 4,5 In a previous paper we have reported on the synthesis of the manganese derivative of 2,3,7,8,12,13,17,18-octamethylcorrole (H 3 OMC). The complex was characterized by elemental analyses and electronic spectroscopy and formulated as [Mn- (OMC)]. 6 Since coordination number 4 is very unusual for Mn(III) complexes, we have now carried out several physical measure- ments to further characterize manganese corrolates and define the metal coordination number and geometry without ambiguity. We then report the synthesis and spectroscopic characterization of several Mn(III) corrolates, which structural formulas are reported in Figure 1, where the peripheral substituents have been varied in order to obtain higher solubility, achieve complete resonance assignment in their 1 H NMR spectra, and define the origin of the isotropic shift. Their axial ligand binding properties in solution have also been investigated. Experimental Section Electronic spectra have been recorded on a Philips PU8700 spec- trophotometer. Electron impact mass spectra were recorded on a VG QUATTRO spectrometer. X-ray photoelectron spectra were run on a Perkin-Elmer PHI 5600ci spectrometer employing an Al KR source (hν ) 1486.6 eV). The working pressure was 2 × 10 -8 Pa. The spectrometer was calibrated by assuming the binding energy (BE) of the Au 4f 7/2 line at 83.9 eV with respect to the Fermi level. The C 1s line of adventitious carbon was assumed at 248.8 eV as internal reference for peak positions. The uncertainty is (0.1 eV. EPR spectra were recorded at 100 K on a Bruker ESP 300 spectrometer operating at 9.44 GHz microwave frequency, 100 KHz field modulation, 20 mW microwave power, and 0.1 mT modulation amplitude; g values were calculated using diphenylpicryl hydrazyl (dpph) as calibrant. The concentrations of the samples ranged from 5 × 10 -2 to 5 × 10 -4 M. Room-temperature susceptibility measurements were obtained by the Gouy method on a permanent magnet (0.7 T) by using a solution of ² Dipartimento di Scienze e Tecnologie Chimiche, Universita ` di Roma Tor Vergata. ‡ Dipartimento di Biologia, Universita ` di Roma Tor Vergata. § Freie Universita ¨t. | Universita ` di Padova. X Abstract published in AdVance ACS Abstracts, March 1, 1997. (1) Licoccia, S.; Paolesse, R. In Metal Complexes with Tetrapyrrole Ligands III; Buchler, J. W., Ed.; Springer-Verlag: Berlin and Heidelberg, Germany, 1995. (2) Bertini, I.; Luchinat, C. In NMR of Paramagnetic Molecules in Biological Systems; Lever, A. B. P., Gray, H. B., Eds.; The B. Cummings Publ. Co.: Menlo Park, CA, 1986. (3) Larson, E. J.; Pecoraro, V. L. In Manganese Redox Enzymes; Pecoraro, V. L., Ed.; VCH Publishers Inc.: New York, 1992. (4) Stern, M. K.; Groves, J. T. In Manganese Redox Enzymes; Pecoraro, V. L., Ed.; VCH Publishers Inc.: New York, 1992. (5) Metalloporphyrins in Catalytic Oxidations; Sheldon, R. A. Ed.; Marcel Dekker Inc.: New York, 1994. (6) Boschi, T.; Licoccia, S.; Paolesse, R.; Tehran, M. A.; Pelizzi, G.; Vitali, F.; J. Chem. Soc., Dalton Trans. 1990, 463. 1564 Inorg. Chem. 1997, 36, 1564-1570 S0020-1669(96)00334-5 CCC: $14.00 © 1997 American Chemical Society