Mononuclear and Binuclear Molybdenum(V) Complexes of the Ligand N,N′-Dimethyl-N,N′-bis(2-mercaptophenyl)ethylenediamine: Geometric Isomers Keith R. Barnard, † Michael Bruck, ‡ Susan Huber, ‡ Carina Grittini, ‡ John H. Enemark, ‡ Robert W. Gable, † and Anthony G. Wedd* ,† School of Chemistry, University of Melbourne, Parkville, Victoria 3052, Australia, and Department of Chemistry, University of Arizona, Tucson, Arizona 85721 ReceiVed July 18, 1996 X The syntheses of mononuclear complexes cis-Mo V OXL (X ) Cl, Br, OMe, OEt, OPh, SPh, NCS, OSiMe 3 ) and two binuclear complexes Mo V 2 O 3 L 2 of the title ligand LH 2 are reported. Two forms of MoOClL, with cis oxo and chloro ligands, were crystallized, one in space group P2 1 /n, with a ) 10.440(2) Å, b ) 14.260(2) Å, c ) 12.041(2) Å,  ) 102.76(2)°, V ) 1748(1) Å 3 , and Z ) 4, and the other in P2 1 /c, with a ) 13.564(4) Å, b ) 7.172(2) Å, c ) 18.242(6) Å,  ) 95.19(1)°, V ) 1767(2) Å 3 , and Z ) 4. MoO(OSiMe 3 )L crystallizes in space group P2 1 /c, with a ) 15.923(3) Å, b ) 11.141(2) Å, c ) 14.186(2) Å,  ) 112.64(2)°, V ) 2323(1) Å 3 , and Z ) 4, while MoO(NCS)L crystallizes in Pna2 1 , with a ) 22.471(2) Å, b ) 12.136(2) Å, c ) 7.138(1) Å, V ) 1947(1) Å 3 , and Z ) 4. The four structures reveal two possible conformations for ligand L: one with trans S atoms (cis,trans-MoOClL and -MoO(OSiMe 3 )L) and one with cis S atoms (cis,cis-MoOClL and -MoO(NCS)L). The cis,cis isomers are converted to the cis,trans forms under reflux in MeCN at 80 °C. Only the cis,trans forms could be isolated for bulkier ligands X (OPh, SPh, OSiMe 3 ). A short H 3 C‚‚‚X interaction is present in the cis,cis forms: C‚‚‚Cl ) 3.07 Å and C‚‚‚N ) 2.93 Å, for X ) Cl and NCS, respectively. Infrared and electronic spectral data provide unambiguous identification of the stereochemistry of ligand L in mononuclear complexes MoOXL. Effective removal of ligand X ) OR from cis,cis-MoO(OR)L (R ) Me, Et) led to two binuclear complexes (Mo V OL) 2 (µ-O) of C i and C 1 point symmetries. C i -(MoOL) 2 (µ-O)‚thf crystallizes in space group P2 1 /c, with a ) 8.5650(5) Å, b ) 15.1862(9) Å, c ) 16.8038(9) Å,  ) 100.183(1)°, V ) 2157.1(8) Å 3 , and Z ) 2, while C 1 -(MoOL) 2 (µ-O)‚CH 2 Cl 2 crystallizes in space group P2 1 /c, with a ) 12.5250(5) Å, b ) 24.673(1) Å, c ) 12.7253(6) Å,  ) 108.070(4)°, V ) 3738.6(3) Å 3 , and Z ) 4. C i -(MoOL) 2 (µ-O)‚thf features two cis,trans- Mo V OXL centers with X ) µ-O, while C 1 -(MoOL) 2 (µ-O)‚CH 2 Cl 2 contains a cis,trans and a cis,cis center. In the latter, the Mo-O-Mo link is asymmetric, allowing relief of steric crowding on the cis,cis side of the molecule. Introduction 1 The pterin-containing molybdenum enzymes catalyze ex- change of an oxygen atom between substrate X and water. 2-6 In formal terms, eqs 1-3 summarize the redox chemistry. Equation 1 seems to be a concerted 2e - event (oxygen atom transfer), while the regeneration of the active site (eq 2) appears to be achieved in two 1e - steps via Mo(V) (coupled electron- proton transfer). 4-6 A combination of X-ray absorption and EPR spectroscopies for various enzymes and for analog species augmented by equilibrium electrochemical techniques has defined the partial coordination spheres at the Mo(VI), Mo(V), and Mo(IV) levels. Figure 1 documents those for two of the more intensively studied oxidase enzymes, sulfite oxidase (SO) and xanthine oxidase (XnO). At least one oxo ligand is proposed for each redox level, and two of the thiolate ligands are supplied by an ene-1,2-dithiolate function of the molyb- dopterin cofactor. 7 A crystal structure for an oxidized form of aldehyde oxidoreductase from DesulfoVibrio gigas reveals a [Mo VI O 2 (OH)] fragment bound by an ene-1,2-dithiolate in a five-coordinate site. 8 A synthetic system based upon cis,trans-Mo VI O 2 L (LH 2 : structure I) has allowed the cis isomers of [Mo V O 2 L] - , Mo V O(OH)L, [Mo V OSL] - , and Mo V O(SH)L to be generated * Corresponding author. E-mail: t.wedd@chemistry.unimelb.edu.au. † University of Melbourne. ‡ University of Arizona. X Abstract published in AdVance ACS Abstracts, January 1, 1997. (1) Abbreviations: EPR, electron paramagnetic resonance; SO, sulfite oxidase; XnO, xanthine oxidase; LH 2, N,N′-dimethyl-N,N′-bis(2- mercaptophenyl)ethylenediamine; L*H2, N,N′-dimethyl-N,N′-bis(2- mercaptoethyl)ethylenediamine; qtlH2, 8-mercaptoquinoline; thf, tet- rahydrofuran. (2) Bray, R. C. Q. ReV. Biophys. 1988, 21, 299. (3) Holm, R. H. Coord. Chem. ReV. 1990, 100, 183. (4) Young, C. G.; Wedd, A. G. In Molybdenum Enzymes, Cofactors and Model Systems; Stiefel, E. I., Coucouvanis, D., Newton, W. E., Eds.; ACS Symposium Series 535; American Chemical Society: Washing- ton, DC, 1993; p 70. (5) Enemark, J. H.; Young, C. G. AdV. Inorg. Chem.1993, 40,1. (6) Young, C. G.; Wedd, A. G. In Encyclopedia of Inorganic Chemistry; King, R. B., Ed.; Wiley: New York, 1994; p 2330. (7) (a) Rajagopalan, K. V. AdV. Enzymol. Relat. Areas Mol. Biol. 1991, 64, 215. (b) Rajagopalan, K. V.; Johnson, J. L. J. Biol. Chem. 1992, 267, 10199. (8) Ramao, M. J.; Archer, M.; Moura, I.; Moura, J. J. G.; LeGall, J.; Engh, R.; Schneider, M.; Hof, P.; Huber, R. Science 1995, 270, 1170. X + Mo VI O ) XO + Mo IV (1) Mo IV + H 2 O ) Mo VI O + 2H + + 2e - (2) net: X + H 2 O ) XO + 2H + + 2e - (3) I 637 Inorg. Chem. 1997, 36, 637-649 S0020-1669(96)00848-8 CCC: $14.00 © 1997 American Chemical Society