2732 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Inorg. Chem. zyxwvuts 1991, 30, 2732-2736 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJ Contribution from the Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255 Oxygenation of a Copper(1) Complex of a Binucleating Macrocyclic Schiff Base Ligand Derived from 1,4,7-Triazaheptane and Furan-2,5-dicarboxaldehyde M. Patrick Ngwenya, Dian Chen, Arthur E. Martell,* and Joseph Reibenspies zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML Received October 4, 1990 The ligand 3,6,9,16,19,22-hexaazatricyclo[22.2.1.1 12,14]octa~- zyxwvut 1 (26),2.9,11 ,I 3,15,22,24-octaene ( (FD)2(DIEN)2) was prepared from 1,4,7-triazaheptane and furan-2,5-dicarboxaldehyde. zyxwvutsrq A dinuclear copper(1) complex is formed by reacting (FD),( DIEN)* with 2 equiv of CU(CH'CN)~(CIO~) in medium formed by a 1:3 mixture of acetonitrile and methanol. The oxygenation reaction of the dinuclear Cu(1) complex was followed spectrophotometrically and by oxygen absorption at pH 9.0 and 5 OC. The crystal structure of the green degradation product formed from the dioxygen complex was determined by X-ray analysis. The results reveal that the copper centers are bridged by hydroxo and methoxo groups. Crystals are monoclinic, space group C2/c, with a = 22.248 (8) A, b = 10.194 (4) A, c = 13.986 (10) A, @ 110.48 (4)O, and zyxwv Z = 4. The C v C u distance is 2.958 (3) A. An unusual coordination mode, which is distorted square planar, is found around each copper atom. The formation of a binuclear Cu(1) dioxygen complex within the macrocycle and the lack of a oxygen insertion reaction are explained on the basis of the bridging oxygen-containing furan groups in place of an aromatic o-xylyl group. Introduction Copper(1) complexes are of relevance because of their occur- rence in natural systems and, in particular, because of their bi- ological function in proteins.' As a result, binuclear copper proteins such as hemocyanin, which serves as an oxygen carrier in molluscs and anthropods? and tyrosinad have attracted a great deal of interest on the part of chemists and biochemists alike, as each group tries to understand the coordination or binding behavior of copper and dioxygen in these systems. As a consequence, many synthetic models of these naturally occurring proteins have been Thus far, much of the most promising research undertaken has placed emphasis on the use of acyclic or open-chain ligands as potential models. For example, Karlin et al. has used open-chain ligands with alkylpyridyl and phenyl groups for modeling tyrosinase and In our endeavor to develop suitable synthetic models that elucidate the active site of oxyhemocyanin and tyrosinase, we have concentrated on the use of macrocyclic ligands, because of their relatively less flexible and more highly preorganized nature, which we anticipate to be well suited for holding coppr(1) ions at appropriate positions for promoting reversible oxygen binding ability in solution.* A typical example is that of our recently published work9 whereby a di- nuclear Cu(1) complex of a macrocyclic ligand, MX2(DIEN)2 (L'), was investigated as a model for tyrosinase. The complex was found to bind molecular oxygen to form the corresponding dinuclear Cu( 11) complex and also resulted in the hydroxylation of the para position of one of the aromatic rings of the ligand. In this work, we report the synthesis of a macrocyclic binucleating Schiff-base ligand, ( FD)2(DIEN)2 (L2), which contains two furan bridge moieties and two terdentate bis(imine) nitrogen sites. The oxygenation of the Cu(1) complex of this ligand in the absence of an endogeneous bridge or oxidizable substrate is also reported. The structural differences between (FD)2(DIEN)2 (L2) and MX2(DIEN)2 (L,) lie in the fact that the phenyl rings found in the latter have been replaced by furan rings in the former, thus Nelson, S. M. In Copper Coordination Chemisrry: Biochemical and Inorgonic Perspecriues; Karlin, K. D., Zubieta, J., Eds.; Adenine Press: New York, 1983. Gaykema, W. P. J.; Volbcda, A.; Hol, W. G. J. J. Mol. Biol. 1985, 187, 255. Wilcox, D. E.; Porras, A. G.; Hwang, Y. T.; Lerch, K.; Winkler, M. E.; Solomon, E. I. J. Am. Chem. Soc. 1985, 107,4015. Tyeklar, Z.; Karlin. K. D. Acc. Chem. Res. 1989, 22, 241. Sorrell, T. N. Tetrahedron 1989, 45, I. Karlin, K. D.; Haka, M. S.; Cruse, R. W.; Meyer, G. J.; Farooq, A.; Gultren, Y.; Hayes, J. C.; Zubieta, J. J. Am. Chem. Soc. 1987, 110, 1196. Karlin, K. D.; Cruse, R. W.; Gultren, Y.; Farooq, A.; Hayes, J. C.; Zubieta, J. J. Am. Chem. Soc. 1987, 109, 2668. Davies, G.; El-Sayed, M. A. Comments Inorg. Chem. 1985, 4, 151. Menif, R.; Martell, A. E. J. Chem. Soc., Chem. Commun. 1989, 1521. removing the possibility of aromatic hydroxylation. Experimental Section Instrumentation. The ligand and metal complex were characterized by standard techniques for compounds, namely, melting-point determi- nation, infrared spectroscopy, nuclear magnetic resonance spectroscopy, and microanalysis for carbon, hydrogen, and nitrogen. Melting point determinations were performed on a Fisher-Johns melting-point appa- ratus. Infrared spectra were recorded on an IBM IR/44 Version 1.0 spectrometer. The oxygen absorption measurements were carried out as previously described.'0 Solid samplcs were used as KBr pellets. The NMR spectra were recorded with a Varian XL 200 spectrometer. Ele- mental analysis for carbon, hydrogen, and nitrogen was carried out by Galbraith Laboratories, Inc., Knoxville, TN. UV-vis spectrophotometric measurements were performed with a Perkin-Elmer Model 553 fast scan UV-vis spectrophotometer. Materials: All reagents and chemicals were of highest grade com- mercial quality and were used without further purification. Funn-2,5-dicarboxaldebyde (1). Initially, one of the precursors, Fu- ran-2,5-dicarboxaldehyde, was prepared by modifying an established method."9l2 Furan-2,S-dimethanoI (4.00 g) was dissolved in CHC13 (400 cm') in a 1000 cm3 round bottomed flask. After complete dissolution, 50 g of molecular sieves (3 A) was added. Thereafter 60 g of activated Mn02 was introduced followed by the addition of more CHC13 (300 cm3). The reaction mixture was left to stir at room temperature for 18 h and filtered, the residue washed with more CHCI', and the volume of solvent reduced to about one-third its original. The solvent was again filtered through a sintered glass funnel of very fine porosity to remove some traces of the activated charcoal. The yellow green solution that resulted was then evaporated to complete dryness. Recrystallization was carried out with a mixture of petroleum ether and chloroform, resulting in a creamy, fluffy solid (1.69 g, yield = 42.0%). Mp: 109-1 10 OC. IH NMR (CDCI'): 7.28 ppm (2 H, singlet, C-CH=O); 9.79 ppm (2 H, singlet, C=CK). 3,6,9,16,19,22-Hexaazatricyclo[22.2.1.1 12*13]octrcosa- 1(26),f9,11,13,15,25~oetrene, (FD)2(DIEN)2 (2). Exactly 1.075 g (10.4 mmol) of DlEN (diethylenetriamine) was dissolved in 400 cm3of pure acetonitrile, in a 1000 cm3 round-bottomed flask. An equivalent amount of furan-2,5-dicarboxaldehyde (1.196 g, 9.64 mmol) was dis- solved separately in 250 cm3of acetonitrile. The latter was then added dropwise to the stirred amine solution over a period of 3 h, during which the color of the solution changed from clear to yellow. The drop rate was continuously monitored (one drop per 2-3 s). The reaction mixture was stirred for 12 h upon which a creamy precipitate was formed. Thereafter the creamy product was filtered, weighed (1.07 g, 53.7% yield) and then recrystallized from a CHClp/MeCN mixture. The IH NMR spectrum of the product was complex indicating the presence of an isomeric mix- ture in solution. Characterization of the product was as follows. Mp: 183-185 OC. Anal. Calcd for C, H and N based on the formula C20H26N602: c, 62.81; H, 6.85; N, 21.97. Found: C, 62.60; H, 6.73; N, 21.88. (IO) Chen, D.; Martell, A. E. Inorg. Chem. 1987, 26, 1026. (1 I) Oleinik, A. F.; Novitski, K. Yu. Zh. Org. Khim. 1970, 6, 2632. (12) Fatiadi, A. J. Synthesis 1976, 5, 65. 0020-1669/91/1330-2732$02.50/0 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCB 0 1991 American Chemical Society