Synthesis and Biradicaloid Character of Doubly Linked Corrole Dimers Satoru Hiroto, ² Ko Furukawa, ‡ Hiroshi Shinokubo,* ,² and Atsuhiro Osuka* ,² Department of Chemistry, Graduate School of Science, Kyoto UniVersity, Sakyo-ku, Kyoto 606-8502, Japan, and CREST & PRESTO, Japan Science and Technology Agency (JST), and Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan Received April 17, 2006; Revised Manuscript Received August 17, 2006; E-mail: hshino@kuchem.kyoto-u.ac.jp; osuka@kuchem.kyoto-u.ac.jp Cyclic π-conjugated systems have attracted considerable interest in terms of their applications as molecular materials having conductive or nonlinear optical properties, as building blocks for supramolecular structures, and for complexation with metals or ions. Our group has developed meso-meso, -, -, triply linked porphyrin oligomers, which exhibit extremely low-energy electronic absorption bands that reach into the infrared region because of the extensive full π-conjugation. 1 Recently, this strategy has been extended to a two-dimensional porphyrin sheet that bears a planar cyclooctatetraene (COT) core, which exhibits paratropic magnetic effects. 2 This direct fusion strategy has been now applied to corrole, a porphyrin-like 18-π aromatic macrocycle except for one direct pyrrole-pyrrole linkage, which displays a unique ability to stabilize unusually high valence state transition metals. 3,4 Some nickel(II) and copper(II) corroles have been reported to show radical charac- ter. 5 We report the synthesis and anomalous properties of the doubly linked corrole dimer 1 and its metal complexes that hold a formal COT moiety in the center of the molecule. Notably, oxidized coun- terparts of 1 and its zinc(II) complex exhibit biradicaloid character. The synthesis of doubly linked corrole dimer 1 began with 2-borylcorrole 2 (Scheme 1). 6 Palladium-catalyzed oxidative cou- pling of 2 using chloroacetone as an oxidant afforded the 2,2′- linked corrole dimer 3 in excellent yield. 7 Further oxidation of 3 with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in toluene provided one product, 4, as an air- and moisture-stable solid in moderate yield. The electronic absorption spectrum of 4 showed a broad spectrum reaching the near-infrared region. Reduction of 4 with NaBH 4 resulted in a solution color change from brown to green and gave 1 quantatively. Its parent mass ion peak was observed at m/z ) 1587.1096 (calcd for (C 74 H 17 N 8 F 30 ) - ) 1587.1103 [(M - H) - ]) in its high-resolution electrospray ionization time-of-flight (HR ESI-TOF) mass spectrum. The 1 H NMR spectrum of 1 elucidated its symmetrical structure, exhibiting one singlet peak (8.91 ppm) and two doublet peaks (8.66 and 8.48 ppm) in the deshielded region. The electronic absorption spectrum of 1 exhibits three main bands at 396, 472, and 721 nm, which are characteristic of corroles but slightly red-shifted compared to those of monomers (Figure 1). DDQ oxidation of 1 yielded 4 quantitatively, indicating that 4 is an oxidized form of 1 (Scheme 2). To gain knowledge about these compounds, we performed the metalation of 1 and 4. When 1 was subjected to the conditions for cobalt metalation of corrole monomers, the bis-cobalt(III) complex 5 was obtained in good yield. On the other hand, 4 was zincated with Zn(OAc) 2 /2H 2 O in refluxing CHCl 3 to afford the bis-zinc complex 6 as a stable brown solid. Since corroles usually serve as ligands for trivalent metals, it is quite rare that a corrole can accommodate divalent metal ions such as the zinc ion. 8 These complexes showed electronic absorption spectra similar to those of the corresponding free bases 1 and 4, respectively, indicating preservation of their electronic and geo- metric structures upon metalation. Complex 6 showed its parent mass ion peak at m/z ) 1714.5249 (calcd for (C 74 H 12 F 30 N 8 Zn 2 ) - ) 1714.5272 ([M] - )) and exhibited very broad (virtually no signal) 1 H NMR spectra in CD 2 Cl 2 and THF-d 8 , even at -90 °C. The structures of the two complexes were finally confirmed by X-ray single-crystal analysis. Curiously, both complexes exhibited quite planar structures, including the COT cores (Figure 2). These ² Kyoto University and JST. ‡ Institute of Molecular Science. Scheme 1 a a Reaction conditions: (a) PdCl2(dppb), chloroacetone, THF, H2O at 70 °C, 6 h, 82%; (b) DDQ, toluene, at 50 °C, 1.5 h; (c) NaBH4, THF, MeOH, room temperature, 30 min, 67% from 3. Figure 1. Electronic absorption spectra of 1 (black solid line), 4 (red solid line), 5 (black dashed line), and 6 (red dashed line). All spectra were recorded in CH2Cl2 solution. Scheme 2 Published on Web 09/01/2006 12380 9 J. AM. CHEM. SOC. 2006, 128, 12380-12381 10.1021/ja062654z CCC: $33.50 © 2006 American Chemical Society