[(μ-SCH2)2CH(OH)]Fe2(CO) - American Chemical Society

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Organometallics 2010, 29, 610–617 DOI: 10.1021/om9009526

Reactions Starting from Diiron Propanedithiolate [(μ-SCH2)2CH(OH)]Fe2(CO)6 Leading to Malonyl-, PPh3-, and [60]Fullerene-Containing Compounds Relevant to the Active Site of FeFe-Hydrogenases Li-Cheng Song,* Xu-Feng Liu, Jiang-Bo Ming, Jian-Hua Ge, Zhao-Jun Xie, and Qing-Mei Hu Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People’s Republic of China Received October 31, 2009

As the active site models of FeFe-hydrogenases, a series of new diiron propanedithiolate compounds (1-7) have been synthesized starting from [(μ-SCH2)2CH(OH)]Fe2(CO)6 (A). Treatment of A with ethyl malonyl chloride or malonyl dichloride in the presence of pyridine gave the malonyl-containing compounds [(μ-SCH2)2CHO2CCH2CO2Et]Fe2(CO)6 (1) and [Fe2(CO)6(μ-SCH2)2CHO2C]2CH2 (2) in 64% and 55% yields, respectively. While A reacted with PPh3 in the presence of Me3NO to give the PPh3-substituted compound [(μ-SCH2)2CH(OH)]Fe2(CO)5(PPh3) (3) in 91% yield, reaction of 3 with malonyl dichloride in the presence of pyridine produced the malonyl-containing compound [Fe2(CO)5(PPh3)(μ-SCH2)2CHO2C]2CH2 (4) in 67% yield. More interestingly, compounds 1, 2, and 4 could react with C60 in the presence of CBr4 and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) via Bingel-Hirsch reaction to afford the [60]fullerene compounds [(μ-SCH2)2CHO2CC(C60)CO2Et]Fe2(CO)6 (5), [Fe2(CO)6(μ-SCH2)2CHO2C]2C(C60) (6), and [Fe2(CO)5(PPh3)(μ-SCH2)2CHO2C]2C(C60) (7) in 36-39% yields. While new compounds 1-7 were characterized by elemental analysis and various spectroscopic methods, 1-4 were further characterized by X-ray crystallography, and the photoinduced H2 evolution catalyzed by 5 was preliminarily investigated.

Introduction Hydrogenases are known to catalyze H2 metabolism in many microorganisms.1-4 According to the metal content in the active site, hydrogenases are primarily classified as FeFehydrogenases (FeFeHases), NiFe-hydrogenases (NiFeHases), *To whom correspondence should be addressed. Fax: 0086-2223504853. E-mail: [email protected]. (1) Adams, M. W. W.; Mortenson, L. E.; Chen, J.-S. Biochim. Biophys. Acta 1981, 594, 105. (2) Adams, M. W. W.; Stiefel, E. I. Science 1998, 282, 1842. (3) Cammack, R. Nature 1999, 397, 214. (4) Nicolet, Y.; Cavazza, C.; Fontecilla-Camps, J. C. J. Inorg. Biochem. 2002, 91, 1. (5) Nicolet, Y.; Lemon, B. J.; Fontecilla-Camps, J. C.; Peters, J. W. Trends Biochem. 2000, 25, 138. (6) Peters, J. W. Curr. Opin. Struct. Biol. 1999, 9, 670. (7) Best, S. P.; Cheah, M. H. Radiat. Phys. Chem. accepted: DOI: 10.1016/j.radphyschem.2009.03.072. (8) Fontecilla-Camps, J. C.; Frey, M.; Garcin, E.; Hatchikian, C.; Montet, Y.; Piras, C.; Vernede, X.; Volbeda, A. Biochimie 1997, 79, 661. (9) Przybyla, A. E.; Robbins, J.; Menon, N.; Peck, H. D. FEMS Microbiol. Rev. 1992, 88, 109. (10) Volbeda, A.; Martin, L.; Cavazza, C.; Matho, M.; Faber, B. W.; Roseboom, W.; Albracht, S. P. J.; Garcin, E.; Rousset, M.; FontecillaCamps, J. C. J. Biol. Inorg. Chem. 2005, 10, 239. (11) Volbeda, A.; Fontecilla-Camps, J. C. Dalton Trans. 2003, 4030. (12) Garcin, E.; Vernede, X.; Hatchikian, E. C.; Volbeda, A.; Frey, M.; Fontecilla-Camps, J. C. Structure 1999, 7, 557. (13) Albracht, S. P. J. Biochim. Biophys. Acta 1994, 1188, 167. (14) Lyon, E. J.; Shima, S.; Buurman, G.; Chowdhuri, S.; Batschauer, A.; Steinbach, K.; Thauer, R. K. Eur. J. Biochem. 2004, 271, 195. pubs.acs.org/Organometallics

Published on Web 01/05/2010

and Fe-hydrogenases (Hmd).5-15 While FeFeHases are mainly used for proton reduction to hydrogen and NiFeHases are used for hydrogen oxidation to protons,16-19 Hmd is utilized to activate hydrogen for use in catabolic processes of microorganisms.14,15 Currently, FeFeHases have attracted much more attention than NiFeHases and Hmd, because of their unusual structure and particularly their extremely rapid rates for production of “clean” and highly efficient H2 fuel.17-22 Recent X-ray crystallography23-25 and FTIR spectroscopy26-28 (15) Shima, S.; Thauer, R. K. Chem. Rec. 2007, 7, 37. (16) Adams, M. W. W. Biochim. Biophys. Acta 1990, 1020, 115. (17) Frey, M. ChemBioChem 2002, 3, 153. (18) Darensbourg, M. Y.; Lyon, E. J.; Smee, J. J. Coord. Chem. Rev. 2000, 206-207, 533. (19) Evans, D. J.; Pickett, C. J. Chem. Soc. Rev. 2003, 32, 268. (20) Lubitz, W.; Tumas, B. Chem. Rev. 2007, 107, 3900. (21) Song, L.-C. Acc. Chem. Res. 2005, 38, 21. (22) Alper, J. Science 2003, 299, 1686. (23) Peters, J. W.; Lanzilotta, W. N.; Lemon, B. J.; Seefeldt, L. C. Science 1998, 282, 1853. (24) Nicolet, Y.; Piras, C.; Legrand, P.; Hatchikian, C. E.; FontecillaCamps, J. C. Structure 1999, 7, 13. (25) Nicolet, Y.; De Lacey, A. L.; Vernede, X.; Fernandez, V. M.; Hatchikian, E. C.; Fontecilla-Camps, J. C. J. Am. Chem. Soc. 2001, 123, 1596. (26) Pierik, A. J.; Hulstein, M.; Hagen, W. R.; Albracht, S. P. J. Eur. J. Biochem. 1998, 258, 572. (27) De Lacey, A. L.; Stadler, C.; Cavazza, C.; Hatchikian, E. C.; Fernandez, V. M. J. Am. Chem. Soc. 2000, 122, 11232. (28) Chen, Z.; Lemon, B. J.; Huang, S.; Swartz, D. J.; Peters, J. W.; Bagley, K. A. Biochemistry 2002, 41, 2036. r 2010 American Chemical Society

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Organometallics, Vol. 29, No. 3, 2010 Scheme 1

studies revealed that FeFeHases contain a unique active site, which consists of a diiron subsite that bears four types of ligands: CO, CN-, [4Fe4S]-S-Cys, and a less defined dithiolate (SCH2)2X (X = CH2, NH, or O) (Scheme 1). Inspired by such structural information, many chemists have designed and synthesized a great number of structural and functional models for the active site of FeFeHases.29-33 This paper reports the synthesis and characterization of seven new diiron propanedithiolate (PDT)-type model compounds obtained by reactions starting from compound [(μ-SCH2)2CH(OH)]Fe2(CO)6 (A). While simple model compounds 1-4 contain a malonyl group and/or one or two PPh3 ligands, the complicated model compounds 5-7 contain an additional π-electron-rich photosensitizer C60 sphere.34,35 Thus, 5-7 could serve as a new class of light-driven models to catalyze proton reduction to hydrogen under the action of light (vide infra).36-39

Results and Discussion Synthesis and Characterization of Malonyl- and PPh3-Containing Compounds [(μ-SCH2)2CHO2CCH2CO2Et]Fe2(CO)6 (1), [Fe2(CO)6(μ-SCH2)2CHO2C]2CH2 (2), [(μ-SCH2)2CH(OH)]Fe2(CO)5(PPh3) (3), and [Fe2(CO)5(PPh3)(μ-SCH2)2CHO2C]2CH2 (4). We found that the C-hydroxyl functionality of parent compound [(μ-SCH2)2CH(OH)]Fe2(CO)6 (A) could (29) For reviews, see for example: (a) Liu, X.; Ibrahim, S. K.; Tard, C.; Pickett, C. J. Coord. Chem. Rev. 2005, 249, 1641. (b) Capon, J.-F.; Gloaguen, F.; Schollhammer, P.; Talarmin, J. Coord. Chem. Rev. 2005, 249, 1664. (c) Fontecilla-Camps, J. C.; Volbeda, A.; Cavazza, C.; Nicolet, Y. Chem. Rev. 2007, 107, 4273. (d) Heinekey, D. M. J. Organomet. Chem. 2009, 694, 2671. (30) Liu, T.; Darensbourg, M. Y. J. Am. Chem. Soc. 2007, 129, 7008. (31) Barton, B. E.; Rauchfuss, T. B. Inorg. Chem. 2008, 47, 2261. (32) Cheah, M. H.; Tard, C.; Borg, S. J.; Liu, X.; Ibrahim, S. K.; Pickett, C. J.; Best, S. P. J. Am. Chem. Soc. 2007, 129, 11085. (33) (a) Eilers, G.; Schwartz, L.; Stein, M.; Zampella, G.; De Gioia, L.; Ott, S.; Lomoth, R. Chem.- Eur. J. 2007, 13, 7075. (b) Ezzaher, S.; Capon, J.-F.; Gloaguen, F.; Petillon, F. Y.; Schollhammer, P.; Talarmin, J. Inorg. Chem. 2009, 48, 2. (c) Windhager, J.; Rudolph, M.; Br€autigam, S.; G€ orls, H.; Weigand, W. Eur. J. Inorg. Chem. 2007, 2748. (d) Song, L.-C.; Li, C.-G.; Gao, J.; Yin, B.-S.; Luo, X.; Zhang, X.-G.; Bao, H.-L.; Hu, Q.-M. Inorg. Chem. 2008, 47, 4545. (e) Wang, W.-G.; Wang, H.-Y.; Si, G.; Tung, C.-H.; Wu, L.-Z. Dalton Trans. 2009, 2712. (f) Zhang, Y.; Hu, M.-Q.; Wen, H.-M.; Si, Y.-T.; Ma, C.-B.; Chen, C.-N.; Liu, Q.-T. J. Organomet. Chem. 2009, 694, 2576. (g) Harb, M. K.; Windhager, J.; Daraosheh, A.; G€orls, H.; Lockett, L. T.; Okumura, N.; Evans, D. H.; Glass, R. S.; Lichtenberger, D. L.; El-khateeb, M.; Weigand, W. Eur. J. Inorg. Chem. 2009, 3414. (h) Wright, R. J.; Lim, C.; Tilley, T. D. Chem.- Eur. J. 2009, 15, 8518. (34) Arbogast, J. W.; Darmanyan, A. P.; Foote, C. S.; Rubin, Y.; Diederich, F. N.; Alvarez, M. M.; Anz, S. J.; Whetten, R. L. J. Phys. Chem. 1991, 95, 11. (35) (a) Balch, A. L.; Olmstead, M. M. Chem. Rev. 1998, 98, 2123. (b) Hirsch, A. The Chemistry of Fullerenes; Thieme Medical Publishers, Inc.: New York, 1994. (36) Song, L.-C.; Tang, M.-Y.; Su, F.-H.; Hu, Q.-M. Angew. Chem., Int. Ed. 2006, 45, 1130. (37) Song, L.-C.; Tang, M.-Y.; Mei, S.-Z.; Huang, J.-H.; Hu, Q.-M. Organometallics 2007, 26, 1575. (38) Song, L.-C.; Wang, L.-X.; Tang, M.-Y.; Li, C.-G.; Song, H.-B.; Hu, Q.-M. Organometallics 2009, 28, 3834. (39) Ott, S.; Kritikos, M.; A˚kermark, B.; Sun, L. Angew. Chem., Int. Ed. 2003, 42, 3285.

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be readily acylated with ethyl malonyl chloride and malonyl dichloride in CH2Cl2 in the presence of pyridine to give the malonyl-containing compounds 1 and 2 in 64% and 55% yields, respectively; in addition, the PPh3-containing compound 3 could be prepared in 91% yield by CO substitution of parent compound A with PPh3 in MeCN in the presence of decarbonylating agent Me3NO,40 whereas treatment of 3 with malonyl dichloride in the presence of pyridine in CH2Cl2 afforded the malonyl- and PPh3-containing compound 4 in 67% yield (Scheme 2). Compounds 1-4 are new and were characterized by elemental analysis and spectroscopy. The IR spectra of 1-4 displayed three to four absorption bands in the range 2078-1938 cm-1 for their terminal carbonyls, whereas complexes 1, 2, and 4 showed two additional absorption bands in the region 1769-1724 cm-1 for their malonate carbonyls. The 1H NMR spectra of 1-4 showed a multiplet in the range 2.24-4.38 ppm for the axial hydrogens attached to middle C atoms in their (CH2S)2CH groups and the corresponding signals in the range 1.25-2.80 ppm for the axial and equatorial hydrogens in their two or four CH2S groups.33d,41 The 13 C NMR spectra of 1-4 showed one signal at about 28 and 73 ppm for C atoms in their CH2S and middle CH groups, respectively. The 31P NMR spectra of 3 and 4 displayed a singlet at about 64 ppm for P atoms in their PPh3 ligands. The molecular structures of 1-4 have been unambiguously confirmed by X-ray crystal diffraction analysis (Figures 1-4 and Table 1). As can be seen intuitively from Figures 1-4, compounds 1 and 3 contain one diiron PDT moiety attached with an ethyl malonate group and a hydroxyl group via the equatorial C9-O7 and C25-O6 bonds, respectively, whereas compounds 2 and 4 have two diiron PDT moieties, which are bridged by a malonate group via the equatorial bonds of C14-O13 and C19-O16 (for 2) or C48-O11 and C53-O14 (for 4), respectively. In addition, similar to those previously reported monophosphine-substituted diiron dithiolate compounds,42 the monophosphine PPh3 ligand in 3 or 4 is located in an apical position of the square-pyramidal iron atom. Synthesis and Characterization of Fullerene-Containing Compounds [(μ-SCH2)2CHO2CC(C60)CO2Et]Fe2(CO)6 (5), [Fe2(CO)6(μ-SCH2)2CHO2C]2C(C60) (6), and [Fe2(CO)5(PPh3)(μ-SCH2)2CHO2C]2C(C60) (7). The light-driven models 5-7 were successfully synthesized by treatment of compound 1, 2, or 4 with C60 in the presence of CBr4 and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) in toluene at room temperature in 36-39% yields (Scheme 3). Compounds 5-7 were synthesized using Bingel-Hirsch reaction, which involves cyclopropanation of C60 with the intermediate Rbromomalonate derivatives of 1, 2, and 4 (formed in situ by bromination of 1, 2, and 4 with CBr4 under the action of organic base DBU).43 (40) (a) Albers, M. O.; Coville, N. J. Coord. Chem. Rev. 1984, 53, 227. (b) Shen, J.-K.; Gao, Y.-C.; Shi, Q.-Z.; Basolo, F. Coord. Chem. Rev. 1993, 128, 69. (41) Winter, A.; Zsolnai, L.; Huttner, G. Z. Naturforsch. 1982, 37b, 1430. (42) (a) Justice, A. K.; De Gioia, L.; Nilges, M. J.; Rauchfuss, T. B.; Wilson, S. R.; Zampella, G. Inorg. Chem. 2008, 47, 7405. (b) Song, L.-C.; Yang, Z.-Y.; Bian, H.-Z.; Liu, Y.; Wang, H.-T.; Liu, X.-F.; Hu, Q.-M. Organometallics 2005, 24, 6126. (c) Song, L.-C.; Wang, H.-T.; Ge, J.-H.; Mei, S.-Z.; Gao, J.; Wang, L.-X.; Gai, B.; Zhao, L.-Q.; Yan, J.; Wang, Y.-Z. Organometallics 2008, 27, 1409. (43) (a) Bingel, C. Chem. Ber. 1993, 126, 1957. (b) Camps, X.; Hirsch, A. J. Chem. Soc., Perkin Trans. 1 1997, 1595.

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Figure 1. Molecular structure of 1 with 30% probability level ellipsoids.

Figure 2. Molecular structure of 2 with 30% probability level ellipsoids.

These products were characterized by elemental analysis and IR, 1H NMR, and 13C NMR spectroscopic methods. The IR spectra of 5-7 showed three absorption bands in the range 2077-1931 cm-1 for their terminal carbonyls, one absorption band at about 1747 cm-1 for their malonate carbonyls, and four absorption bands in the range 1433-525 cm-1 typical of the C-C stretching vibrations for their C60 spheres.44 The 1H NMR spectra of 5-7 are similar to those of their precursors 1, 2, and 4, except that the singlets in the region 2.80-3.30 ppm for methylene groups of their precursors disappeared. This is consistent with formation of a three-membered ring from one of the [6, 6] bonds of C60 and the malonate methylene group of precursor 1, 2, or 4 via BingelHirsch reaction.43 The 13C NMR spectra of 5-7 further proved their structures. For example, the single-butterfly (44) (a) Hare, J. P.; Dennis, T. J.; Kroto, H. W.; Taylor, R.; Allaf, A. W.; Balm, S.; Walton, D. R. M. J. Chem. Soc., Chem. Commun. 1991, 412. (b) Song, L.-C.; Yu, G.-A.; Su, F.-H.; Hu, Q.-M. Organometallics 2004, 23, 4192.

Figure 3. Molecular structure of 3 with 30% probability level ellipsoids.

[2Fe2S] cluster compound 5, as shown in Figure 5, displays 23 resonance signals in the region 136-145 ppm, one signal

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Table 1. Selected Bond Lengths (A˚) and Angles (deg) for 1-4 1 Fe(1)-S(1) Fe(1)-S(2) Fe(1)-Fe(2) Fe(2)-S(1)

2.2478(9) 2.2401(8) 2.5148(6) 2.2437(8)

Fe(2)-S(2) O(7)-C(9) O(7)-C(10) C(10)-C(11)

2.2640(8) 1.462(3) 1.349(3) 1.497(4)

S(2)-Fe(1)-S(1) S(1)-Fe(1)-Fe(2) S(2)-Fe(1)-Fe(2) S(1)-Fe(2)-S(2)

85.44(3) 55.87(2) 56.51(2) 84.97(3)

S(1)-Fe(2)-Fe(1) S(2)-Fe(2)-Fe(1) Fe(2)-S(1)-Fe(1) C(10)-C(11)-C(12)

56.03(2) 55.61(2) 68.10(2) 111.7(2)

Fe(1)-S(1) Fe(1)-S(2) Fe(1)-Fe(2) Fe(2)-S(1)

2.2624(8) 2.2578(9) 2.5139(6) 2.2457(8)

Fe(2)-S(2) Fe(3)-Fe(4) O(13)-C(14) O(16)-C(19)

2.2543(9) 2.5079(7) 1.463(3) 1.451(3)

S(2)-Fe(1)-S(1) S(1)-Fe(2)-Fe(1) S(2)-Fe(2)-Fe(1) Fe(2)-S(1)-Fe(1) Fe(2)-S(2)-Fe(1)

84.88(3) 56.42(2) 56.21(2) 67.79(3) 67.72(3)

S(2)-Fe(1)-Fe(2) S(1)-Fe(1)-Fe(2) S(1)-Fe(2)-S(2) O(13)-C(14)-C(13) O(16)-C(19)-C(20)

56.08(2) 55.79(2) 85.35(3) 105.23(19) 104.6(2)

Fe(1)-S(1) Fe(1)-S(2) Fe(1)-Fe(2) Fe(2)-S(1)

2.2689(8) 2.2578(7) 2.5256(8) 2.2648(8)

Fe(2)-S(2) Fe(2)-P(1) O(6)-C(25) S(1)-C(24)

2.2715(8) 2.2571(9) 1.445(3) 1.821(2)

S(2)-Fe(1)-S(1) S(1)-Fe(2)-Fe(1) S(2)-Fe(2)-Fe(1) Fe(2)-S(1)-Fe(1) Fe(2)-S(2)-Fe(1)

84.82(3) 56.224(17) 55.85(2) 67.71(2) 67.78(3)

S(2)-Fe(1)-Fe(2) S(1)-Fe(1)-Fe(2) S(1)-Fe(2)-S(2) P(1)-Fe(2)-Fe(1) P(1)-Fe(2)-S(1)

56.37(2) 56.07(3) 84.60(2) 157.84(2) 111.51(2)

Fe(1)-S(1) Fe(1)-S(2) Fe(1)-Fe(2) Fe(2)-S(1)

2.2597(8) 2.2559(7) 2.5256(6) 2.2916(8)

Fe(2)-S(2) Fe(2)-P(1) Fe(3)-P(2) Fe(3)-Fe(4)

2.2558(8) 2.2483(8) 2.2579(8) 2.5291(6)

S(2)-Fe(1)-S(1) S(2)-Fe(1)-Fe(2) S(1)-Fe(1)-Fe(2) S(1)-Fe(2)-S(2) S(1)-Fe(2)-Fe(1)

84.92(4) 55.96(2) 56.90(2) 84.19(3) 55.70(2)

S(2)-Fe(2)-Fe(1) Fe(2)-S(1)-Fe(1) Fe(1)-S(2)-Fe(2) P(1)-Fe(2)-Fe(1) P(2)-Fe(3)-Fe(4)

55.96(2) 67.41(3) 68.08(2) 154.16(2) 156.30(2)

2

3

Figure 4. Molecular structure of 4 with 30% probability level ellipsoids. Scheme 3

4

at 70.08 ppm, and one signal at 50.41 ppm. The former 23 signals can be assigned to 58 sp2-C atoms in its C60 sphere, whereas the latter two signals represent two sp3-C atoms in its C60 sphere and the methano bridge C atom in its threemembered ring, respectively.43 Theoretically, compound 5, with Cs symmetry, should have 32 13C NMR signals for its C60 sphere.35 However, we observed only 24 signals for its C60 sphere owing to the overlap of some signals in very close proximity.45 In addition, the double-butterfly [2Fe2S] cluster (45) (a) Green, M. L. H.; Stephens, A. H. H. J. Chem. Soc., Chem. Commun. 1997, 793. (b) Song, L.-C.; Liu, J.-T.; Hu, Q.-M.; Wang, G.-F.; Zanello, P.; Fontani, M. Organometallics 2000, 19, 5342.

compound 7, as shown in Figure 6, exhibits 15 resonance signals in the range 138-146 ppm, which can be attributed to 58 sp2-C atoms in its C60 sphere. The signal appearing at 70.77 ppm represents two sp3-C atoms in its C60 sphere, and the signal at 50.80 ppm can be assigned to the methano bridge C atom in its three-membered ring.43 Actually, the 13C NMR spectrum of compound 7 showing 16 signals for its C60 sphere is consistent with its C2v symmetry (theoretically showing 17 signals); this is because there are two theoretical signals overlapped at 144.73 ppm.35,45 Unfortunately, the crystal structures of 5-7 have not been determined yet by X-ray crystal diffraction method, since it is too difficult to grow suitable single crystals of these C60containing model compounds for X-ray diffraction analysis. Photoinduced H2 Evolution Catalyzed by Light-Driven Model 5. Usually, the photoinduced catalytic system for H2 production mainly consists of four separate components: an electron donor, a photosensitizer, a catalyst, and a proton source.46-49 (46) Okura, I. Coord. Chem. Rev. 1985, 68, 53. (47) Ozawa, H.; Haga, M.; Sakai, K. J. Am. Chem. Soc. 2006, 128, 4926. (48) Rau, S.; Walther, D.; Vos, J. G. Dalton Trans. 2007, 915. (49) Fihri, A.; Artero, V.; Razavet, M.; Baffert, C.; Leibl, W.; Fontecave, M. Angew. Chem., Int. Ed. 2008, 47, 564.

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Figure 5. (a) Original 13C NMR spectrum of 5. (b) Expanded 13C NMR spectrum of 5.

Figure 6. (a) Original 13C NMR spectrum of 7. (b) Expanded 13C NMR spectrum of 7.

However, recently we and others utilized a three-component system (which includes an electron donor, proton source, and a light-driven model that contains a photosensitizer moiety attached to catalyst, a simple active site model) to achieve such photoinduced H2 production;38,50 in addition, a possible pathway for the photoinduced H2 production catalyzed by a light-driven model (which contains a porphyrin moiety and a simple model) was briefly suggested, as shown in Figure 7.38 Now, we report a new example of such photoinduced H2 production catalyzed by light-driven model 5 in which a photosensitizer C60 moiety is covalently connected to the skeleton of simple model 1. First, in order to know if the (50) Li, X.; Wang, M.; Zhang, S.; Pan, J.; Na, Y.; Liu, J.; A˚kermark, B.; Sun, L. J. Phys. Chem. B 2008, 112, 8198.

photoexcited electron of the C60 moiety in 5 could be intramolecularly transferred to the catalytic diiron active site, we studied the UV-vis absorption and fluorescence emission spectra of 5. This is because such an electron transfer (ET) process is one of the important steps required for proton reduction to H2 performed by light-driven models. The UV-vis absorption spectra of 5 along with free C60 and simple model 1 were determined under the same conditions for comparison. As can be seen in Figure 8, compound 5 displays three strong absorption bands at 228, 256, and 325 nm, whereas free C60 exhibits three strong bands at 229, 258, and 329 nm. Obviously, the former three bands are caused by the C60 moiety in compound 5 since they are just slightly blue-shifted by 1-4 nm relative to the latter three bands caused by free C60. In addition, the strongest band of free C60, at 258 nm, becomes much weaker than the

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Figure 7. Possible pathway for the photoinduced H2 production catalyzed by a light-driven model.

Figure 9. Fluorescence emission spectra of 5, C60, and an equimolar mixture of 1 with C60 (λex = 300 nm) in CH2Cl2 (1  10-5 M).

not by an intermolecular collision process between molecules of 5.57 On the basis of the aforementioned spectral studies, we carried out the expected photoinduced H2 production in the presence of light-driven model 5. The light irradiation of a solution of 5, electron donor EtSH, and proton source CF3CO2H gave small amounts of H2. This intriguing finding will be fully developed in a future report.

Conclusion -5

Figure 8. UV-vis spectra of 5, C60, and 1 in CH2Cl2 (1  10

M).

corresponding one caused by the C60 moiety in compound 5, whereas simple model 1 shows only two very weak bands, at 228 and 330 nm. Although numerous UV-vis spectra of free C60 and its derivatives were previously determined under different conditions,51-53 reported UV-vis spectral studies on a dyad compound consisting of C60 and a [2Fe2S] cluster are very few.54 The fluorescence emission spectra of 5 along with free C60 (for C60 and its derivatives, the fluorescence emission spectra were also previously reported)55,56 and an equimolar mixture of free C60 with simple model 1 were determined under the same conditions for comparison. As shown in Figure 9, they all display one sharp band at about 600 nm and one broad band centered at about 700 nm. While the first sharp band of 5 is just red-shifted by ca. 1 nm relative to that of free C60, its intensity is considerably quenched relative to the intensity of free C60, with a quenching efficiency of 48%. Since the intensity of the first band of the equimolar mixture is virtually the same as that of free C60, it is believed that the decreased intensity of the first band of 5 could be mainly attributed to the intramolecular ET from the photoexcited photosensitizer C60 moiety to the diiron active site and (51) Taylor, R.; Hare, J. P.; Abdul-Sada, A. K.; Kroto, H. W. J. Chem. Soc., Chem. Commun. 1990, 1423. (52) Song, L.-C.; Wang, G.-F.; Liu, P.-C; Hu, Q.-M. Organometallics 2003, 22, 4593. (53) An, Y.-Z.; Rubin, Y.; Schaller, C.; McElvany, S. W. J. Org. Chem. 1994, 59, 2927. (54) Westmeyer, M. D.; Galloway, C. P.; Rauchfuss, T. B. Inorg. Chem. 1994, 33, 4615. (55) Lin, S.-K.; Shiu, L.-L.; Chien, K.-M.; Luh, T.-Y.; Lin, T.-I. J. Phys. Chem. 1995, 99, 105. (56) Catal an, J.; Elguero, J. J. Am. Chem. Soc. 1993, 115, 9249.

The simple model compounds 1-4 and light-driven models 5-7 have been successfully prepared by various synthetic methods. While simple models 1 and 2 are prepared by acylation of A with ethyl malonyl chloride or malonyl dichloride, 3 and 4 are made by CO substitution of A with PPh3 and acylation of 3 with malonyl dichloride, respectively. More interestingly, light-driven models 5-7 are shown to be prepared by Bingel-Hirsch reaction of simple models 1, 2, and 4 with C60 in the presence of CBr4 and DBU. New model compounds 1-7 have been structurally characterized, whereas the photoinduced proton reduction to H2 catalyzed by light-driven model 5 is preliminarily studied. Further studies on structural modification of such lightdriven models to improve their photoinduced catalytic activity for H2 production are in progress in this laboratory.

Experimental Section General Comments. All reactions were performed using standard Schlenk and vacuum-line techniques under an atmosphere of nitrogen. Dichloromethane was distilled over P2O5 and acetonitrile over CaH2 under N2. Toluene was purified by distillation under N2 from sodium/benzophenone ketyl. C60, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), CBr4, PPh3, Me3NO 3 2H2O, and pyridine were available commercially and used as received. Compound [(μ-SCH2)2CH(OH)]Fe2(CO)6,33d ethyl malonyl chloride,58 and malonyl dichloride59 were prepared (57) (a) Dudie, M.; Lhotak, P.; Kral, V.; Lang, K.; Stibor, I. Tetrahedron Lett. 1999, 40, 5949. (b) Baskaran, D.; Mays, J. W.; Zhang, X. P.; Bratcher, M. S. J. Am. Chem. Soc. 2005, 127, 6916. (58) Breslow, D. S.; Baumgarten, E.; Hauser, C. R. J. Am. Chem. Soc. 1944, 66, 1286. (59) McCloskey, A. L.; Fonken, G. S.; Kluiber, R. W.; Johnson, W. S. Organic Syntheses; Wiley: New York, 1963; Collect. Vol. 4, p 261.

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Table 2. Crystal Data and Structure Refinement Details for 1-4

mol formula mol wt cryst syst space group a/A˚ b/A˚ c/A˚ R/deg β/deg γ/deg V/A˚3 Z Dc/g cm-3 abs coeff/mm-1 F(000) index ranges no. of rflns no. of indep rflns 2θmax/deg R Rw gooodness of fit largest diff peak and hole/e A˚-3

1

2

3

4

C14H12Fe2O10S2 516.06 triclinic P1 7.9643(16) 11.486(2) 11.532(2) 95.098(2) 94.811(2) 106.411(2) 1001.4(3) 2 1.711 1.705 520 -9 e h e 6 -13 e k e 13 -13 e l e 13 5472 3519 50.06 0.0287 0.0770 1.044 0.391/-0.365

C21H12Fe4O16S4 871.95 triclinic P1 9.371(16) 12.755(2) 14.676(3) 72.226(11) 72.158(10) 66.825(9) 1500.5(5) 2 1.930 2.125 868 -11 e h e 10 -14 e k e 15 -17 e l e 17 14 256 5273 50.04 0.0280 0.0607 0.997 0.651/-0.332

C26H21Fe2O6PS2 636.22 monoclinic P2(1)/c 9.2085(18) 17.506(4) 16.610(3) 90 102.28(3) 90 2616.4(9) 4 1.615 1.370 1296 -12 e h e11 -23 e k e13 -20 e l e21 18 891 6224 55.78 0.0392 0.0869 1.053 0.408/-0.491

C55H42Fe4O14P2S4 1340.47 monoclinic P2(1)/c 14.370(3) 18.366(4) 21.399(4) 90 92.28(3) 90 5643(2) 4 1.578 1.277 2728 -18 e h e14 -23 e k e24 -22 e l e28 40 926 13 455 55.82 0.0411 0.0880 1.061 0.420/-0.422

according to the published methods. Preparative TLC was carried out on glass plates (26  20  0.25 cm) coated with silica gel G (10-40 μm). IR spectra were recorded on a Bio-Rad FTS 6000 or Nicolet MAGNA 560 FTIR photospectrometer. 1 H NMR, 31P NMR, and 13C NMR spectra were obtained on a Bruker Avance 300 or 400 NMR or a Varian Mercury Plus 400 NMR spectrometer. Elemental analyses were performed on an Elementar Vario EL analyzer. Melting points were determined on a Yanaco MP-500 apparatus and are uncorrected. Preparation of [(μ-SCH2)2CHO2CCH2CO2Et]Fe2(CO)6 (1). To a solution of [(μ-SCH2)2CH(OH)]Fe2(CO)6 (A) (0.120 g, 0.30 mmol) in CH2Cl2 (15 mL) at 0 °C was added ethyl malonyl chloride (0.06 mL, 0.50 mmol) and pyridine (0.04 mL, 0.50 mmol). The reaction mixture was stirred at 0 °C for 15 min and then at room temperature for 45 min. Volatiles were removed under vacuum, and the residue was subjected to TLC separation using CH2Cl2/petroleum ether (v/v = 2:1) as eluent. From the main red band, 1 was obtained as a red solid (0.099 g, 64%), mp 96-98 °C. Anal. Calcd for C14H12Fe2O10S2: C, 32.58; H, 2.34. Found: C, 32.69; H, 2.41. IR (KBr disk): νCtO 2073 (s), 2038 (vs), 1986 (vs), 1951 (m); νCdO 1758 (s), 1729 (s) cm-1. 1H NMR (300 MHz, CDCl3): 1.26 (t, 3H, J = 6.6 Hz, CH3), 1.64 (t, 2Ha, JHaHe = JHaHa0 = 12.0 Hz), 2.78 (dd, 2He, JHeHa = 9.6 Hz, JHeHa0 = 3.0 Hz), 3.30 (s, 2H, O2CCH2CO2), 4.18 (q, 2H, J = 6.6 Hz, CH2CH3), 4.32-4.38 (m, 1Ha0 ) ppm (in this paper Ha and He denote the axially and equatorially bonded H atoms in CH2S groups, while Ha0 and He0 represent those axially or equatorially bonded to the bridgehead C atom). 13C NMR (75.4 MHz, CDCl3): 14.03 (CH3), 26.58 (SCH2), 41.34 (O2CCH2CO2), 61.72 (CH2CH3), 74.44 (CH), 164.80, 165.94 (CdO), 207.03, 207.12 (CtO) ppm. Preparation of [Fe2(CO)6(μ-SCH2)2CHO2C]2CH2 (2). To a solution of A (0.200 g, 0.50 mmol) in CH2Cl2 (15 mL) at 0 °C was added pyridine (0.05 mL, 0.62 mmol) and malonyl dichloride (0.03 mL, 0.30 mmol). The reaction mixture was stirred at 0 °C for 15 min and then at room temperature for 45 min. After removal of volatiles at reduced pressure, the residue was subjected to TLC using CH2Cl2/petroleum ether (v/v = 2:1) as eluent. From the main orange-red band, 2 was obtained as a red solid (0.120 g, 55%), mp 200-202 °C (in a sealed capillary). Anal. Calcd for C21H12Fe4O16S4: C, 28.93; H, 1.39. Found: C, 28.91; H, 1.38. IR (KBr disk): νCtO 2078 (vs), 2037 (vs), 1992 (vs); νCdO 1769 (s), 1749 (s) cm-1. 1H NMR (300 MHz, CDCl3):

1.62 (t, 4Ha, JHaHe = JHaHa0 =11.7 Hz), 2.73 (d, 4He, JHeHa = 12.6 Hz), 3.23 (s, 2H, O2CCH2CO2), 4.28-4.35 (m, 2Ha0 ) ppm. 13 C NMR (75.4 MHz, CDCl3): 26.55 (SCH2), 41.00 (O2CCH2CO2), 74.68 (CH), 164.31 (CdO), 207.08 (CtO) ppm. Preparation of [(μ-SCH2)2CH(OH)]Fe2(CO)5(PPh3) (3). To a solution of A (0.120 g, 0.30 mmol) and PPh3 (0.079 g, 0.30 mmol) in MeCN (20 mL) was added Me3NO 3 2H2O (0.033 g, 0.30 mmol), and then the mixture was stirred at room temperature for 1 h. Volatiles were removed under vacuum to give a residue, which was subjected to TLC using CH2Cl2 as eluent. From the main red band, 3 was obtained as a red solid (0.173 g, 91%), mp 233-234 °C (in a sealed capillary). Anal. Calcd for C26H21Fe2O6PS2: C, 49.08; H, 3.33. Found: C, 49.19; H, 3.31. IR (KBr disk): νCtO 2039 (vs), 1987 (vs), 1938 (s); νOH 3616 (m) cm-1. 1H NMR (400 MHz, CDCl3): 1.02 (s, 1H, OH), 1.26 (t, 2Ha, JHaHe = JHaHa0 = 11.2 Hz), 2.14 (d, 2He, JHeHa = 11.2 Hz), 2.24-2.30 (m, 1Ha0 ), 7.47, 7.67 (2s, 15H, 3C6H5) ppm. 31P NMR (162 MHz, CDCl3, 85% H3PO4): 64.92 (s) ppm. 13C NMR (75.4 MHz, CDCl3): 29.86 (SCH2), 72.85 (CH), 128.58, 128.71, 130.38, 133.27, 133.41, 135.52, 136.05 (C6H5), 209.05, 213.54, 213.67 (CtO) ppm. Preparation of [Fe2(CO)5(PPh3)(μ-SCH2)2CHO2C]2CH2 (4). The same procedure was followed as for 2, but 0.318 g (0.50 mmol) of 3 was employed in place of A. A 0.225 g (67%) amount of 4 was obtained as a red solid, mp 238-240 °C (in a sealed capillary). Anal. Calcd for C55H42Fe4O14P2S4: C, 49.28; H, 3.16. Found: C, 49.39; H, 3.18. IR (KBr disk): νCtO 2046 (vs), 1988 (vs), 1961 (s), 1945 (s); νCdO 1758 (m), 1724 (m) cm-1. 1H NMR (300 MHz, CDCl3): 1.25 (t, 4Ha, JHaHe = JHaHa0 = 12.0 Hz), 2.04 (dd, 4He, JHeHa = 12.6 Hz, JHeHa0 = 4.2 Hz), 2.80 (s, 2H, O2CCH2CO2), 3.42-3.51 (m, 2Ha0 ), 7.42, 7.62-7.68 (s, m, 30H, 6C6H5) ppm. 31P NMR (121 MHz, CDCl3, 85% H3PO4): 63.27 (s) ppm. 13C NMR (75.4 MHz, CDCl3): 26.53 (SCH2), 40.83 (O2CCH2CO2), 75.33 (CH), 128.49, 128.61, 130.35, 133.40, 133.55, 135.07, 135.61 (C6H5), 163.63 (CdO), 208.90, 213.45, 213.59 (CtO) ppm. [(μ-SCH2)2CHO2CC(C60)CO2Et]Fe2(CO)6 (5). To a solution consisting of 1 (0.041 g, 0.078 mmol), CBr4 (0.026 g, 0.078 mmol), C60 (0.040 g, 0.055 mmol), and toluene (30 mL) was added DBU (23.8 μL, 0.159 mmol), and then the reaction mixture was stirred at room temperature overnight. Volatiles were removed under vacuum, and the residue was subjected to TLC separation using CH2Cl2/petroleum ether (v/v = 4:3) as

Article eluent. From the purple band, C60 (0.015 g) was recovered. From the main brown band, 5 was obtained as a brown solid (0.016 g, 39% based on the consumed C60), mp >300 °C (in a sealed capillary). Anal. Calcd for C74H10Fe2O10S2: C, 71.99; H, 0.82. Found: C, 71.80; H, 0.93. IR (KBr disk): νCtO 2074 (s), 2035 (vs), 1998 (vs); νCdO 1748 (s); νC60 1432 (m), 1178 (m), 580 (s), 527 (s) cm-1. 1H NMR (300 MHz, CDCl3): 1.48 (t, 3H, J = 7.2 Hz, CH3), 1.85 (t, 2Ha, JHaHe = JHaHa0 = 12.0 Hz), 2.95 (dd, 2He, JHeHa = 8.7 Hz, JHeHa0 = 4.2 Hz), 4.54 (q, 2H, J = 7.2 Hz, CH2CH3), 4.67-4.74 (m, 1Ha0 ) ppm. 13C NMR (100.6 MHz, oC6D4Cl2): 13.06 (CH3), 25.67 (SCH2), 50.41 (O2CCCO2), 62.24 (OCH2), 74.70 (CH), 160.60, 161.66 (CdO), 206.00 (CtO), C60: 70.08 (2sp3-C), 136.94 (2C), 138.69 (2C), 139.48 (2C), 139.60 (2C), 140.30 (2C), 140.44 (2C), 140.71 (3C), 141.39 (2C), 141.56 (4C), 141.61 (4C), 142.36 (2C), 142.44 (2C), 143.08 (1C), 143.19 (4C), 143.23 (4C), 143.28 (2C), 143.33 (2C), 143.43 (2C), 143.55 (2C), 143.69 (4C), 143.76 (2C), 143.83 (4C), 144.16 (2C) ppm. Preparation of [Fe2(CO)6(μ-SCH2)2CHO2C]2C(C60) (6). To a solution consisting of 2 (0.091 g, 0.104 mmol), CBr4 (0.035 g, 0.104 mmol), C60 (0.050 g, 0.069 mmol), and toluene (30 mL) was added DBU (16 μL, 0.107 mmol), and then the reaction mixture was stirred at room temperature overnight. After removal of the volatiles at reduced pressure, the residue was subjected to TLC using CH2Cl2/petroleum ether (v/v = 2:3) as eluent. From the purple band, C60 (0.012 g) was recovered. From the main brown band, 6 was obtained as a brown solid (0.032 g, 38% based on the consumed C60), mp >300 °C (in a sealed capillary). Anal. Calcd for C81H10Fe4O16S4: C, 61.17; H, 0.63. Found: C, 60.90; H, 0.87. IR (KBr disk): νCtO 2077 (s), 2037 (vs), 1999 (vs); νCdO 1750 (m); νC60 1428 (w), 1200 (m), 581 (m), 527 (w) cm-1. 1H NMR (300 MHz, CDCl3): 1.81 (t, 4Ha, JHaHe = JHaHa0 = 12.0 Hz), 2.91 (dd, 4He, JHeHa = 12.9 Hz, JHeHa0 = 4.2 Hz), 4.59-4.69 (m, 2Ha0 ) ppm. 13C NMR (100.6 MHz, CS2/CDCl3): 27.08 (SCH2), 50.95 (O2CCCO2), 76.56 (CH), 161.59 (CdO), 207.07 (CtO), C60: 70.97 (2sp3-C), 139.15 (4C), 141.34 (4C), 141.93 (4C), 142.43 (4C), 143.23 (4C), 143.34 (4C), 143.40 (2C), 144.11 (4C), 144.59 (4C), 144.71 (2C), 144.97 (4C), 145.03 (8C), 145.24 (2C), 145.51 (4C), 145.61 (4C) ppm. Preparation of [Fe2(CO)5(PPh3)(μ-SCH2)2CHO2C]2C(C60) (7). To a solution consisting of 4 (0.209 g, 0.156 mmol), CBr4 (0.053 g, 0.156 mmol), C60 (0.075 g, 0.104 mmol), and toluene (30 mL) was added DBU (24 μL, 0.160 mmol), and then the reaction mixture was stirred at room temperature overnight. Volatiles were removed to give a residue, which was subjected to TLC separation using CH2Cl2/petroleum ether (v/v = 2:3) as eluent. From the purple band, C60 (0.014 g) was recovered. From the main brown band, 7 was obtained as a brown solid (0.063 g, 36% based on the consumed C60), mp >300 °C (in a sealed capillary). Anal. Calcd for C115H40Fe4O14P2S4: C, 67.08; H, 1.96. Found: C, 66.98; H, 2.27. IR (KBr disk): νCtO 2042 (vs), 1982 (vs), 1931 (s); νCdO 1744 (s); νC60 1433 (m), 1185 (w), 581 (m), 525 (s) cm-1. 1H NMR (300 MHz, CDCl3): 1.47 (t, 4Ha, JHaHe = JHaHa0 = 12.9 Hz), 2.23 (d, 4He, JHeHa = 12.9 Hz), 3.79-3.85 (m, 2Ha0 ), 7.46, 7.70 (2s, 30H, 6C6H5) ppm. 31P NMR (162 MHz, CDCl3, 85% H3PO4): 63.91 (s) ppm. 13C NMR (75.4 MHz, CDCl3): 26.66 (SCH2), 50.80 (O2CCCO2), 76.90 (CH), 128.58, 128.71, 130.49, 133.35, 133.50, 135.09, 135.62 (C6H5),

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160.71 (CdO), 208.88, 213.35, 213.48 (CtO), C60: 70.77 (2sp3C), 138.92 (4C), 140.97 (4C), 141.53 (4C), 142.18 (4C), 142.97 (4C), 143.12 (4C), 143.26 (2C), 143.90 (4C), 144.39 (2C), 144.56 (4C), 144.73 (8C), 144.87 (4C), 144.96 (2C), 145.27 (4C), 145.36 (4C) ppm. Photoinduced H2 Evolution Catalyzed by Light-Driven Model 5. A 30 mL Schlenk flask equipped with a N2 inlet tube, a serum cap, a magnetic stir-bar, and a water-cooling jacket was charged with model 5 (1.23 mg, 0.001 mmol), EtSH (7.4 μL, 0.10 mmol), CF3CO2H (7.4 μL, 0.10 mmol), and THF (10 mL). While stirring, the resultant solution was deoxygenated by bubbling with nitrogen for at least 10 min, and then it was irradiated using a 500 W Hg lamp at about 25 °C (controlled by the cooling jacket) for 0.5 h. During the light irradiation, the evolved H2 was withdrawn periodically using a gastight syringe, which was analyzed by gas chromatography on a Shimadazu GC-2014 instrument with a thermal conductivity detector and a carbon molecular sieve column (3 mm  2.0 m) and N2 as the carrier gas. X-ray Structure Determinations of 1-4. Single crystals of 1-4 suitable for X-ray diffraction analyses were grown by slow evaporation of the CH2Cl2/petroleum ether solution of 1 at -20 °C or the CH2Cl2/hexane solutions of 2-4 at -10 °C, respectively. A single crystal of 1 or 3 was mounted on a Bruker SMART 1000 automated diffractometer. Data were collected at room temperature using a graphite monochromator with Mo KR radiation (λ = 0.71073 A˚) in the ω-φ scanning mode. Absorption correction was performed by the SADABS program.60 A single crystal of 2 or 4 was mounted on a Rigaku MM007 (rotating anode) diffractometer equipped with a Saturn 70CCD. Data were collected at 113(2) K, using a confocal monochromator with Mo KR radiation (λ = 0.71070 A˚) in the ω-φ scanning mode. Data collection, reduction, and absorption correction were performed by the CRYSTALCLEAR program.61 All the structures were solved by direct methods using the SHELXS-97 program62 and refined by full-matrix least-squares techniques (SHELXL-97)63 on F2. Hydrogen atoms were located using the geometric method. Details of crystal data, data collections, and structure refinements are summarized in Table 2.

Acknowledgment. We are grateful to the National Natural Science Foundation of China and the Tianjin Natural Science Foundation for financial support. Supporting Information Available: Full tables of crystal data, atomic coordinates and thermal parameters, and bond lengths and angles for 1-4 as CIF files. This material is available free of charge via the Internet at http://pubs.acs.org. (60) Sheldrick, G. M. SADABS, A Program for Empirical Absorption Correction of Area Detector Data; University of G€ottingen: Germany, 1996. (61) CRYSTALCLEAR 1.3.6; Rigaku and Rigaku/MSC: The Woodlands, TX, 2005. (62) Sheldrick, G. M. SHELXS97, A Program for Crystal Structure Solution; University of G€ottingen: Germany, 1997. (63) Sheldrick, G. M. SHELXL97, A Program for Crystal Structure Refinement; University of G€ottingen: Germany, 1997.