Bonding, Activation, and Stabilization of Small Molecules by

Chapter 21

Bonding, Activation, and Stabilization of Small Molecules by Molybdenum—Sulfur and Iron—Sulfur Systems

Downloaded by PENNSYLVANIA STATE UNIV on December 6, 2015 | http://pubs.acs.org Publication Date: July 26, 1993 | doi: 10.1021/bk-1993-0535.ch021

Dieter Sellmann Institut für Anorganische Chemie der Universität Erlangen-Nuernberg, Egerlandstrasse 1, W-8520 Erlangen, Germany

In quest for model compounds for oxidoreductases with [MoS] and/or [FeS] centers, coordination, activation, and stabilization of CO, NO, N , N H , N H , N H , NH3, NH O, and NH2 by Mo and Fe sulfur ligand complexes was investigated. Reduction of NO to NH OH was achieved at [Mo(NO)('S4')] centers. [Mo(η -N H )(NO)('S ')] and [Mo (CO) (' S ') ] model structure and, potentially, function of the Mo centers in [Fe/Mo] nitrogenases. [Fe(L)('N S ')] complexes (L = CO, N H , Ν Η , NH ) yield a new model for the active centers of [Fe/Fe] and possibly also [Fe/Mo] nitrogenases. ('N S ' = 2,2'bis(2-mercaptophenylthio)diethylamine(2-); 'S ' = 1,2-bis(2-mer captophenylthio)ethane(2-); ' S2 - = 3,5-di(tertiarybutyl)-benzene -1,2-dithiolate(2-)). 2

2

2

2

3

2

4

2

2

2

2

IV

3

4

bu

2

2

2

H

2

2

2

4

4

3

2-

H

4

2-

4

bu

2

Activation of stable and stabilization of unstable molecules has been a long standing challenge for chemists. When [MoS] enzymes are the topic, inevitably nitrogenases and molecules such as the inert N and the elusive nitrogen hydrides N H , N H or N H 3 come into mind (7). All nitrogenases, however, contain by far more iron, and one nitrogenase contains exclusively iron (2). Thus, if chemists want to design systems that are either equally efficient as nitrogenases or allow deeper insights into the mechanisms and elementary steps of No fixation, iron-sulfur complexes are at least equally important. [MS] centers also occur in other oxidoreductases that catalyze reactions that are extremely difficult in chemical terms. What makes [MS] centers particularly suited to catalyze these reactions which require not only activation and stabilization of molecules, but also addition and release of substrates and transfer of electrons and protons? Answers to these questions may be obtained from model complexes, which may be mononuclear even though die [MS] centers of native proteins are polynuclear. 2

2

2

0097-6156/93/0535-0332$06.00A) © 1993 American Chemical Society

In Molybdenum Enzymes, Cofactors, and Model Systems; Stiefel, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

2

2

21. SELLMANN

Bonding, Activation, and Stabilization of Small Molecules

333

Ligands and complexes Suitable model compounds should have a relatively robust [MS] core and vacant sites for the coordination of substrates. For this purpose polydentate thioetherthiolate ligands were designed (scheme I) (J).


Scheme I

2

2

R = H: V "

X = S: *$ ' ' (R = H), 5

,bu

2

,

R = t-bu: S ' -

,bu

2

S ' ' (R = t-bu) 5

2

X = NH: N S ' - (R = H),

4

H

4

,bu

2

N S * - (R = t-bu) H

4

The 'XS/2" ligands allow variation of the coordination sphere of a given complex in a defined way by substituting thioether S for amine Ν or ether Ο donors. These ligands coordinate high-valent as well as low-valent molybdenum. The resulting complex fragments prefer either hard or soft coligands as is shown for a series of'S^ complexes in scheme II. l

Scheme Π: Molybdenum complexes with'S^ " ligands

% ^ ςϊψ? ¥ ¥ m

[Mo(0) ('S4 )] 2

,

it

ν

[Fe(NH )(»N S ')] Downloaded by PENNSYLVANIA STATE UNIV on December 6, 2015 | http://pubs.acs.org Publication Date: July 26, 1993 | doi: 10.1021/bk-1993-0535.ch021

3

H

RVNA'MtfWW]

4

change of spin state (inert labile)

[FeCN S ')],(N H4) H

4

2

a low-spin [FeCNS^)]" entity. Protonation-deprotonation reactions in protein environments are not unusual, and if they could cause such spin-state changes of Fe centers, the iron centers would indeed become strong candidates for binding N in all types of nitrogenases. In contrast, complexes with the 4 d metal molybdenum always exhibit low-spin configurations. It is ironic that in a book that focuses on molybdenum we propose the importance of iron. However, the predominance of iron at the active site makes this an idea which might be worthwhile to pursue, particulary in the light of the X-ray structural model of the FeMo cofactor (D. C. Rees et al., Chapter 11) reported briefly after this article had been completed. 2

Acknowledgment I thank my coworkers who are cited in the references for their dedication, hard work, and willingness to share my hopes and disappointments. Support of our investigations by the Deutsche Forschungsgemeinschaft, Fonds der Chemischen Industrie and Bundesministerium fur Forschung und Technologie is gratefully acknowleged.

Literature Cited (1) a) Lowe, D. J.; Thorneley, R. N. F.; Smith, Β. E. In Metalloproteins Part 1, Metal Proteins with Redox Roles; Harrison P., Ed.; Verlag Chemie, Weinheim, 1985. b) Eady, R. R. In 'Perspectives on Bioinorganic Chemistry; Hay, R. W.; Dilworth, J. R.; Nolan, Κ. B. Eds.; JAI Press, London, 1991, 225. (2) Chiswell, J. R.; Premakumar, R.; Bishop, P. E.; J. Bacteriol. 1988, 170, 27. (3) a) Sellmann, D.; Jonk, H. E.; Pfeil, H. R.; Huttner, G.; v. Seyerl, J.J.Organomet. Chem. 1980, 191, 171. b) Sellmann, D.; Reisser, W. Z. Naturforsch. 1984, 39b, 1268. c) Sellmann, D.; Freyberger, G.; Eberlein, R.; Böhlen, Ε.; Huttner, G.; Zsolnai, L. J. Organomet. Chem. 1987, 323, 21. d) Sellmann, D.; Kleine -Kleffmann,U. J. Organomet. Chem. 1983, 258, 315. e) Sellmann, D.; Kunstmann, H.; Knoch, F.; Moll, M . Inorg. Chem. 1988, 27, 4183. f) Sellmann, D.; Binker, G.; Moll, M.; Hardtweck, E. J. Organomet. Chem. 1987, 327, 403. g) Sellmann, D.; Soglowek, W.; Moll, M. Z. Naturforsch., 1992, 47b, 1105.



344

MOLYBDENUM ENZYMES, COFACTORS, AND MODEL SYSTEMS

(4) a) Sellmann, D.; Zapf, L. Z. Naturforsch. 1985, 40b, 368. b) Sellmann, D.; Kaul, Β. Β. Z. Naturforsch. 1983, 38b, 562. c) Sellmann, D.; Pöhlmann, G.; Knoch, F.; Moll, Μ. Ζ. Naturforsch. 1988, 44b, 312. d) Sellmann, D.; Schwarz, J. J. Organomet. Chem. 1983, 241, 343. e) Sellmann, D.; Weiss, R.; Knoch, F. Inorg. Chim. Acta 1990, 175, 65. f) Sellmann, D.; Seubert, B.; Knoch, F.; Moll, M . Z. Allg. Anorg. Chem. 1991, 600, 95. g) Sellmann, D.; Binker, G.; Schwarz, J.; Knoch, F.; Boese, R.; Huttner, G.; Zsolnai, L. J. Organomet. Chem. 1987, 323, 323. (5) Cole, J. Α.: Assimilatory and Dissimilatory Reduction of Nitrate to Ammonia. In The Nitrogen and Sulphur Cycles'. Cole, J. Α.; Ferguson, S. J.; Eds. Cambridge University Press, 1988, 281. (6) a) McCleverty, J. A. Chem. Rev. 1979, 79, 53. b) The metal mediated electrochemical NO reduction to give various products ranging from N O , N2 and NH2OH to NH has been described by other groups. (T. J. Meyer et al., Inorg Chem. 1991, 30, 629 and references cited therein.) (7) a) Sellmann, D.; Seubert, B.; Moll, M.; Knoch, F. Angew. Chem. 1988, 100, 1221; Angew. Chem. Int. Ed. Engl. 1988, 27, 1164. b) Sellmann, D.; Seubert, B.; Knoch, F.; Moll, M . Z. Naturforsch. 1991, 46b, 1449. (8) a) Wieghardt, K.; Quilitzsch, U. Z. Naturforsch. 1991, 36b, 683. b) Wieghardt, K. Adv. Inorg. Bioinorg. Mech. 1984, 3, 213. (9) Sellmann, D.; Seubert, B. Angew. Chem. 1992, 104, 200; Angew. Chem. Int. Ed. Engl. 1992, 31, 205. (10) a) Sellmann, D.; Kern, W.; Holzmeier, Α.; Pöhlmann, G.; Moll, Μ. Ζ. Naturforsch. 1991, 46b, 1349. b) Hannakam, M . Thesis University of Erlangen, 1992. (11) Sellmann, D.; Kern, W.; Pöhlmann, G.; Knoch, F.; Moll, M . Inorg. Chim. Acta 1991, 185, 155. (12) a) Schrock, R. R.; Liu, A. H.; O'Regan, M . B.; Finch, W. C.; Payack, J. P. Inorg. Chem. 1988, 27, 3574. b) Vogel, F.; Barth, Α.; Huttner, G.; Klein, T.; Zsolnai, L.; Kremer, R. Angew. Chem. 1991, 103, 325; Angew. Chem. Int. Ed. Engl. 1991, 30, 303. (13) Burgess, Β. K. Chem. Rev. 1990, 90, 1377. (14) a) Erler, B. S.; Dewan, J. C.; Lippard, S. J. Inorg. Chem. 1981, 20, 2719. b) Crayston, J. Α.; Almond, H. J.; Downs, A. J.; Poliakoff, M.; Turner, J. J. Inorg. Chem. 1984, 23, 3051. c) Lazarowych, N. J.; Morris, R. H. Can. J. Chem. 1990, 68, 558. (15) a) Sellmann, D.; Grasser, F.; Knoch, F.; Moll, M . Angew. Chem. 1991, 103, 1346; Angew. Chem. Int. Ed. Engl. 1991, 30, 1311; b) Inorg. Chim. Acta 1992, in press. (16) Mueller-Westerhoff, U. T.; Vance, B. In Compr. Coord. Chem.; Wilkinson, G.; Gillard, R. D.; McCleverty, J. Α.; Eds.; Pergamon, Oxford, 1987, Vol2, 595. (17) a) Chatt, J.; Dilworth, J. R.; Richards, R. L. Chem. Rev. 1977, 78, 589. b) Henderson, R. A. Leigh, G. J. Pickett, Ch. J. Adv. Inorg. Chem. Radiochem. 1983, 27, 198. (18) a) Sellmann, D.; Weiss, W. Angew. Chem. 1977, 89, 918; Angew. Chem. Int. Ed. Engl. 1977, 16, 880; ibid. 1978, 90, 295; 1978, 17, 269; b) J. Organomet. Chem. 1978, 160, 183. (19) Yoshida, T.; Adachi, T.; Kaminaka, M.; Ueda, T. J. Am. Chem. Soc. 1988, 110, 4872. (20) Sellmann, D.; Soglowek, W.; Knoch, F.; Ritter, G.; Dengler, J. Inorg. Chem. 1992, 31, 3711. (21) Sellmann, D.; Kunstmann, H.; Moll, M.; Knoch, F. Inorg. Chim. Acta 1988, 154, 157. (22) Albright, T. Α.; Burdett, J. K.; Whangbo, M . H. Orbital Interactions in Chemistry; Wiley, New York, 1985. 2

3


21. SELLMANN

Bonding, Activation, and Stabilization of Small Molecules

(23) Sellmann, D.; Fünfgelder, S.; Pöhlmann, G.; Knoch, F.; Moll, M . Inorg. Chem. 1990, 29, 4772. (24) Foner, S. N.; Hudson, R. L. J. Chem. Phys. 1978, 68, 3162. (25) Sellmann, D.; Soglowek, W.; Knoch, F.; Moll, M . Angew. Chem. 1989, 101, 1244; Angew. Chem. Int. Ed. Engl. 1989, 28, 1271. (26) Sellmann, D.; Brandi, Α.; Endell, R. J. Organomet. Chem. 1975, 90, 309. April 12,1993


RECEIVED


345

Bonding, Activation, and Stabilization of Small Molecules by

Recommend Documents