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(5) J. W. Buchler, Home-Seyler’s 2.Physiol. Chem., 359, 1065 (1978). (6) (a) E. B. Fleischer and R. V. Ferra, Inorg. Biochem., 10, 91 (1979); (b) R. F. Pasternack and E. Halliwell, J. Am. Chem. SOC., 101, 1026 (1979): (c) J. S.Valentine and A. E. Quinn, Inorg. Chem.. 15, 1997 (1976); (d) D. R. Paulson, A. W. Addison, D. Dolphin, and B. R. James, J. Biol. Chem., 254, 7002 (1979). (7) M. M. L. Chu, C. E. Castro, and G. M. Hathaway, Biochemistry, 17, 481 (1978). (8)(a) J. W. Buchler and P. D. Smith, Angew. Chem., Int. Ed. Engl., 13, 745 (1974):(b) A. Antipas, J. W. Buchler, M. Gouterran, and P. D. Smith, J. Am. Chem. SOC., 100,3015 (1978). (9) (a) J. W. Buchler, W. Kokisch, and P. D. Smith, manuscript in preparation: (b) W. Kokisch, Doctoral Thesis, Technische Hochschule Aachen, 1979; (c) W. Kokisch, Diplomarbeit, Technische Hochschule Aachen, 1976; (d) P. D. Smith, unpublished experiments, 197611977: (e) P. D. Smith, Doctoral Thesis, Technische Hochschule Aachen, 1976; (f) J. W. Buchler, W.Kokisch, and P. D. Smith, Struct. Bonding (Berlin), 34, 79 (1978). (10) Os(OEP)(1-Meim)2,9ad [ O S ( O E P ) ( ~ - M ~ ~ ~ ) and Z ] P[0~(OEP)py2]Bph~~ F~,~ were characterized by elemental analyses, ’H NMR, optical, and infrared spectra. For selected spectral data, see ref 9f. Additionally, the effective magnetic moments have been determined for [Os(OEP)py2]CI04 by the ) of [Os(OEPHNH&]BF4 with a Faraday balance NMR method (1.52 1 ~and (Dr. H. Lueken. Aachen: 1.85 FB, Curie law, 70-300 K).B8 (11) G. M. Brown, F. R. Hopf, T. J. Meyer, and D. G. Whitten, J. Am. Chem. Soc., 97,5385 (1975). (12) J. Billecke and J. W. Buchler, unpublished experiments. (13) R. C. Bray, G. N. Mautner, E.M. Fieiden, and C. I.Carle in “Superoxide and Superoxide Dismutase”, A. M. Michelson, J. M. McCord, and I. Fridovich, Eds., Academic Press, London, 1977, p 61. (14) M. R. Green, H. A. 0. Hill, and D. R. Turner, F€BS Lett., 103, 176 (1979). (15) M. E. Peover and B. S. White, Nectrochim. Acfa, 11, 1061 (1966). Neither the osmochrome nor the dioxygen potential is altered by addition of 1% water to pyridine solutions. Obviously the electrodes do not indicate eq 9 although the latter exists in the bulk of the solution. (16) J. Billecke, Diplomarbeit, Technische Hochschule Aachen, 1977. (17) A more detailed report of this work will appear in “Superoxide and Superoxide Dismutase”, Elsevier, New York, in press.
Jochen Billecke, Wolfgang Kokisch Institut f u r Anorganische Chemie Technische Hochschule Aachen 0 - S I 0 0 Aachen, West Germany J. W. Buchler* Fachbereich Anorganische Chemie und Kernchemie Technische Hochschule Darmstadt 0-6100 Darmstadt, West Germany Received November 14, 1979
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Table 1. Bond Distances and Angles in M O O ~ [ S C ( C H ~ ) ~ C H ~ Nand H CRelated H ~ ] ~ Complexes 4
1
5
Mo-S( 1) Mo-S( 2) Mo-O( 1) Mo-O( 2) Mo-N( 1) Mo-N(2) S(1I-W)
Bond Distances, A 2.420 (3) 2.420 ( I ) 2.409 (3) 2.409 (1) 1.723 ( 5 ) 1.699 (2) 1.711 (5) 1.705 (2) 2.262 (9) 2.372 (2) 2.277 (8) 2.510 (2) 2.764 (5) [4.71]
S( I)-Mo-S(2) O( l)-M0-0(2) N( I)-Mo-N(2) S(l)-Mo-O(l) S(2)-M0-0(2) S( l)-M0-0(2) S(2)-Mo-O( 1) S( l)-Mo-N( 1) S(2) -Mo-N( 2) S( l)-Mo-N(2) S(2)-Mo-N( 1) O( l)-Mo-N( 1) 0(2)-Mo-N(2) O( I)-Mo-N(2) 0(2)-Mo-N( 1)
Bond Angles, deg 69.8 (19) 154.3(3) 122.2 (3) 107.9 (1) 144.0 (3) 107.7 (3) 107.5 (2) 118.3 (2) 120.4 (2) 72.9 (3) 74.6 (2) 142.6 (2) 141.0 (2) 81.8 (3) 83.0 (3) 80.5 (3) 80.3 (3)
2.41 1 (3) 2.411 (3) 1.694 (6) 1.712 (7) 2.382 (9) 2.374 (9) [4.75] 160.9 ( I ) 106.3 (3)
Complex 1, containing the ligand (CH3)NHCH2C(CH3)2S-, was prepared as part of our program to design and synthesize new bi-, tri-, tetra- and pentadentate ligands containing N, s,and 0 donor atoms. The variety of ligand types is such that some arrangement of the donor atom sets is likely to be analogous to that present in Mo enzymes. In this paper we restrict our attention to complexes 1-3 of the bidentate ligands derived from cysteamine. ,NR& (R3)f = L(RdXC, S-
A Nonoctahedral Dioxo Molybdenum Complex with a Coordinated Partial Disulfide Bond
complex (MoO,L,)
ligand (L-)
= R, = H;R, = R, = CH, R, = R, = R, = CH,;R, = H R, = R, = R, = H;R, = CH, The Mo(V1) complexes were prepared by the reaction
R,
1 2 3
Sir: EXAFS studies on the oxidized forms of sulfite oxidase’ and xanthine oxidase2 have implicated the presence of terminal oxygen atoms at an Mo-0 distance of -1.7 A and approxiMoOz(acac)z 2LH Mo02L2 2 acacH mately three sulfur atoms in the Mo(V1) coordination sphere. where acac = acetylacetonate. The striking similarity of the EXAFS patterns for oxidized at 0 OC in CH30H directly from sulfite oxidase’ and M O ~ ~ [ C H ~ S C H ~ C H ~ N ( C H ~ CCrystals H ~ S )of~ 1]were ~ ~ grown ~ the reaction mixture. The compound crystallizes in the led to the suggestion that the Mo coordination sphere of the monoclinic space grou P21/c with a = 10.688 (3), b = 11.923 enzyme may contain two cis oxo groups, two mutually trans ( 2 ) , c = 14.032 (3) ; p = 106.65 (2)’. The structure was thiolates each cis to both oxo donors, and one thioether linkage solved by standard heavy-atom methods and was refined using trans to an oxo group as found in the crystallographic study full-matrix least squares to R = 4.9% and R , = 5.4% as deof the ~ o m p l e xThe . ~ above and other structural discussions5 scribed previously6 using 1516 reflections with F2bsd > on the Mo(V1) state in Mo oxidases have uniformly been based 3U(F,$,,d). ,411 nonhydrogen atoms were refined anisotropically on the assumptions of a conventional octahedral structure and and hydrogen atoms were included as fixed contributions in two independently acting thiolate donor atoms. In this paper the final least-squares cycles. we present the results of studies on the seemingly simple The structure of 1 displayed in the figure has noncrystalloMo(V1) complex M O O ~ [ C H ~ N H C H ~ C ( C H ~(l), ) ~ which S]Z graphic twofold symmetry with the C2 axis bisecting the Sreveal a distinctly nonoctahedral structure and a partial S-S Mo-S, O-Mo-O, and N-Mo-N bond angles. Distances and bond within the “Mo(V1)” coordination sphere. Moreover, the angles are displayed in Table I along with corresponding values ‘ H N M R spectra of this and related Mo(V1) complexes for Mo0z[(CH3)2NCH2CH2N(CH2CH2S)2l4(4) and demonstrate stereochemical nonrigidity which is sensitive to M002(8-mercaptoquinolinato)2~(5), other complexes conthe nature of the ligand. Since these structural features must taining Mo02N2S2 coordination spheres. be considered in discussions of the Mo coordination sphere in Inspection of Table I and Figure 1 reveals the nonoctahedral enzymes, we also discuss in a preliminary way some of the nature of the structure There are no atoms present at sites potential biochemical implications of these findings.
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steric or electronic interactions which would be present were the standard octahedral geometry adopted. By comparison with earlier results one might have anticipated the placement of the two Mo-S linkages mutually trans and cis to the 0 atoms. However, this geometry would result in steric interference between the two methyl groups on adjacent N atoms (which are forced into pseudoequatorial positions of their respective chelate rings in order to avoid 1-3 interactions with the CH3-su'bstituted thiolate-bearing carbon). To avoid this interaction, two different octahedral structures are possible in which, respectively, either one or two S atoms lie trans to Mo-Ot. Although this placement is sterically acceptable, it may be electronically unfavorable as it places the strongly nand a-donating S and otdonors in competition for the same set of p and d orbitals along the hypothesized S-Mo-Ot axis. Figure 1. Molecular structure of MoO~[SC(CH~)~CH~NH(CH~)]Z Evidently the steric and electronic constraints conspire to (1). produce the resultant structure in which steric hindrance is indeed minimized and there are no groups trans to the Mo-Ot trans to either Mo-Ot bond. The largest angle for any 0linkages. Mo-X group.is only 122' and that is the angle for X = 0. The detailed reasons for the adoption of this unusual geThere are also no near-octahedral trans angles between any ometry are being investigated by structural examination of pair of Mo-S and Mo-N bonds. Although the structure is not other complexes in the series. We have found that a combiclose to an octahedron, it can be described as a severe distortion nation of NMR and IR spectroscopic studies may be suggestive from an octahedral trans-Moo2 complex with mutually cis of certain structural trends. The Mo-0 stretching vibrations N atoms and mutually cis S atoms. Opening the N-Mo-N of 1 at 883 and 858 cm-' are exceptionally low, probably reangle in this hypothetical structure to 1.44' while the 0-Mo-0 flecting the opening of the 0 - M o - 0 angle, the slight lengthangle closes toward this opening yields the observed structure. ening and weakening of the Mo-Ot bond, and possibly the H This structure has been aptly dubbed by Keperts as a skewbonding found in the solid state. The 220-MHz IH NMR trapezoidal bipyramid and previously had only been identified spectrum of 1, at 17 'C in CDC13, shows the presence of for complexes of Sn.8 equivalent C-bound methyl groups, while the solid-state The appropriateness of the skew-trapezoidal bipyramidal structure in the figure shows inequivalent CH3 groups on the structural designation is enforced by examination of the plane thiolate-bearing carbon. The N M R equivalence of the methyl containing the Mo and its N and S donor atoms. Deviations groups is probably caused by a molecular rearrangement from the least-squares plane determined by Mo, S( l), S(2), process within the Mo(V1) coordination sphere. N(1), and N(2) are -0.002,0.210, -0.207, -0.132, and 0.131 Results on 1 are contrasted with data on A for the respective atoms. The 0 atoms lie above and below M O O ~ [ N H ~ C ( C H ~ ) ~ C(3), H ~which S ] ~ displays infrared the plane at 1.491 and 1.517 A and the Mo-O(1)-O(2) plane absorptions at 907 and 872 cm-I, closer to those for complexes is nearly perpendicular to it (dihedral angle = 87.8'). The 4 and 5, which are known to have trans-dithiolate octahedral dihedral angle between the planes determined by Mo, S( l), structure^.^,' The NMR spectrum of 3 at 17 OC shows two and N ( l ) and Mo, S(2), and N(2) is 13.7', this being the resonances for the CH3 groups and AB patterns for the CH2 largest dihedral angle for any Mo-inclusive set of three atoms and NH2 protons, consistent with an octahedral structure with within the plane. While the trapezoidal plane is only approxtrans thiolate and cis amine donors. imate, the deviations are sufficiently small to endorse the vaThese structural and dynamic results reveal that the sixlidity of the skew-trapezoidal bipyramidal designation for coordinate Mo(V1) sphere may be more prone to distortions descriptive purpose^.^ than had been previously surmised. Relatively subtle changes A further unique feature of the resent structure is the in ligand between 1 and 3 apparently produce a dramatic S-Mo-S angle of 69.8' and the 2.76- separation of the sulfur structural change in both the static and dynamic properties of atoms within the coordination sphere. This distance is far the Mo(V1) sphere. Clearly, small changes in steric requireshorter than the van der Waals contact of 3.7 AIo and is also ments of protein or cofactor ligands might also impose unusual shorter than the nominal 3.4-A distance expected" for two S structural features or impart fluxionality to the Mo(V1) sphere atoms bound to the same metal atoms. The Mo-S bond diswithin the enzyme. Further, the presence of a partial disulfide tances at -2.42 are very close to those in earlier Mo(V1) structure^^^^ as well as to those in the Mo(V1) state of sulfite bond must also be considered. The assignment of the short S-S distance in 1 to a partial oxidase. disulfide bond deserves both additional justification and further In the solid state, each molecule of M002L2 is hydrogen comment. Sulfur-sulfur distances comparable with the 2.76-A bonded to two other molecules to form infinite chains. It is not clear to what extent this H-bonding pattern contributes to the distance in 1 have been found in several structures where this formation of the unusual structure. The infrared spectrum of interaction clearly plays a bonding r ~ l e . ' ~ Perhaps -'~ the most 1 in KBr or in Nujol mull shows peaks assignable to v(Mo-0) vivid case is the 2.83-A transannular S(3)-S(8) distance in at 883 and 858 cm-I. These values are significantly lower than sS2+which, from both structuralI2 and theoreticalI3 studies, has been assigned as a bonding interaction. Other examples v(Mo-0) for 4 (921 and 893 cm-l) and 5 (921 and 888 cm-I). We are planning to analyze structurally Mo02of S-S partial bonds include S5N6 with S-S = 2.43 and [ ( C H ~ ) ~ N C H Z C ( C H ~(2), ) ~ Swhere ]~ the dimethyl-subS4N402(0CH3)- with S-S = 2.48 A. In various dithiolene complexes the S-S distance of 3.05 8, has been considered as stituted nitrogen precludes the possibility of such H bonding. As 2 also has extremely low frequency v(Mo-0) vibraa bonding interaction.I6 Thus, the 2.76-A distance in 1 may tions, it seems certain that the observed intermolecular H bondrepresent the formation of a partial disulfide bond which reing is not the sole determinant of the unusual geometrical quires concomitant transfer of charge to the Mo center. A reand spectroscopic properties of M o O ~ [ C H ~ N H C H ~ C cent structural study" of the Mo(V) complex M O @ ~ ( S C ~ Hshowed ~ ) ~ - ~one of the two molecules in the unit (CH312SI 2.20 Why does this seemingly simple complex adopt such an cell to have an interligand S-S distance of 2.94 A which also unusual structure? The answer seems to lie in the unfavorable was considered to be indicative of S-S overlap.
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Melding our results with those in the literature leads to a fascinating possibility for redox processes in Mo-bis(thio1ate) systems. As illustrated below, successive one-electron oxidation of Mo(IV) to (formally) Mo(V) and Mo(V1) may involve a substantial component of thiolate-disulfide oxidation. If this S-R - 1 ~ - R-S -. S-R R-S, ,S-R --le-- R-S
. ..
\ /
le-
Acknowledgment. This work was supported by N S F Grants CHE 77-07026 and 79-26021 (to E.I.S. and J.L.C.) and PCM 79-17105 (to K.O.H.). We are grateful to Professor Rupert A. D. Wentworth and the N M R Staff of Indiana University for giving us the opportunity to obtain the 220-MHz spectra described herein. Supplementary Material Available: A list of atomic coordinates and thermal parameters for M O O ~ [ S C ( C H ~ ) Z C H ~ N H(1C page). H~]~ Ordering information is given on any current masthead page. References and Notes Cramer, S. P.; Gray, H. B.; Rajagopalan. K. V. J. Am. Chem. SOC.1979, 101, 2772. Tullius, T. D.; Kurtz, D. M.; Conradson, S. D.; Hodgson, K. 0. J. Am. Chem. SOC. 101, 1979,2776. Cramer, S.P.; Hodgson, K. 0.; Stiefel. E. I.; Newton, W. E. J. Am. Chem. Soc. 1978. 100. 2748. _.. Berg, J. M.; Hcdgson, K. 0.; Cramer, S. P.; Corbin, J. L.; Elsberry, A.; Pariyadath, N.; Stiefel, E. I. J. Am. Chem. SOC. 1979, 101. 2774. Stiefel. E. I. Progr. Inorg. Chem. 1977,22, 1. Stiefel E. I. In "Molybdenum and Molybdenum Containing Enzymes", Coughlan, M. P., Ed.; Pergamon Press: Elmsford, N.Y., and Oxford, 1980;Chapter 2,p 41. Bobrik, M. A,; Hodgson, K. 0.;Holm, R. H. Inorg. Chem. 1977, 16, 1851. This paper describes the X-ray data reduction and refinement procedures used in the investigation reported here. Yamanouchi, K.; Enemark, J. H. Inorg. Chem. 1979, 18,1626. Kepert, D. L. Prog. Inorg. Chem. 1977, 23,1. An alternative description in terms of a severely distorted trigonal prism wherein the triangular faces have slid past each other is also possible. Detailed considerations of geometrical criteria and further structural documentation will be presented elsewhere. Paulina, L. "The Nature of the Chemical Bond"; Cornell University Press: lthaca;N.Y., 1960;p 260. (11) Dance, I. G.; Wedd, A. G.; Boyd, I. W. Aust. J. Chem. 1978, 31,519. f12\ -, Gillesoie. R. J.: Passmore.. J.:. Ummat. P. K.; Vaidva, 0.C. Inorg. Chem. .
1971,-io, 1327. (13)Saiahub, D.; Foti, A. E.; Smith V. H., Jr. J. Am. Chem. SOC.1978, 100, 7847. (14)Chivers, T.; Proctor, J. J. Chem. SOC.,Chem. Commun. 1978,642. (15)Roesky, H. W.; Wilt, M.; Krebs, B.; Jurgen-Korte, H. Angew. Chem., ht. Ed. fngl. 1979, 18,415. (16)Eisenberg, R. Prog. Inorg. Chem. 1970, 12,295. (17)Musker. W. K.: Wolford. T. L. J. Am. Chem. SOC. 1976,98, 3055. (18)Musker, W. K.; Roush, P. B. J. Am. Chem. SOC.1978, 98, 6745.
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Edward I. Stiefel,* Kenneth F. Miller Alice E. Bruce, James L. Corbin Contribution No. 691 Charles F. Kettering Research Laboratory Yellow Springs, Ohio 45387 Jeremy M. Berg, Keith 0. Hodgson Department of Chemistry, Stanford University Stanford, California 94305 Received November 9, 1979 Synthesis, Structure, and Reactivity of Mercurial Derivatives of an Organoruthenium Cluster Sir:
Hydrido organotrimetallic clusters of ruthenium are interesting model compounds for the study of transition metal cluster chemistry for several reasons. One reason is that they provide easily synthesized examples of thermally stable monohydride derivatives of the Ru3 cluster with which to study the reactivity of the kz-hydrido bond. During the course of our studies on the general reactivity of H R u ~ ( C O ) ~ ( C ~(I)' H~) we discovered that C6H5HgX (X = Br, I) reacts with I to give
4
Ru
I
a halomercury(I1) derivative ( C ~ H ~ ) R U ~ ( C O )(11) ~ Hand ~X an equivalent amount of b e n ~ e n e : ~ . ~ ( C ~ H ~ ) R U ~ ( 4-C C6H5HgX ~)~H THF reflux
-(C,H~)RU~(CO)~H~X + C6H6 (1) 12 h II,30-40%, I1 has been fully characterized and the data are summarized in Table I for the bromo and iodo derivatives. We subsequently found that reaction of the anion of I (generated in situ4 with HgX2 (X = Br, I) also gives I1 in comparable yields:
+ K+ + HgX2 25 "hC I1
I
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Wilson, G. S.; Swanson, D. D.; Klug, J. T.; Glass, R. G.; Ryan, M.D.: Musker, W. K. J. Am. Chem. SOC. 1979, 101, 1040. NOTE ADDED. IN PROOF. The crystal structure of Moo2[(CH~)ZNCHZC(CH~)ZS]* (2) has been solved. A structure of the skewtrapezoidal bipyramidal type is again found.
. \MoVT /
leMd v MoV partial S-S bond formation occurs in Mo enzymes (and none of the existent data preclude such an occurrence), then it could explain, in part, the absence of identity between the spectroscopic, redox, and catalytic properties of Mo enzymes and their "model" systems. For example, the high g z and low A,(95*97Mo)value of the Mo(V) EPR signal in xanthine oxidase5 may be attributable to strong delocalization of the unpaired electron into a partial S-S bond. The great range of redox potentials for different Mo enzymes (while also potentially explainable in other terms) could likewise be due to varying degrees of S-S bond formation in the different molybdenum enzymes. The presence of strategically juxtaposed sulfides in large-ring multisulfur organic heterocyclic compounds has been found to correlate with substantially lower potentials for one-electron oxidation and with increased reversibility in the electron-transfer p r o ~ e s s . Similarly, ~ ~ - ~ ~ the specific cis positioning of Mo-bound thiolates may be responsible for unusual reactivity and spectroscopic features of Mo sites in enzymes. Regardless of the relevance of the above results to Mo enzymes, it is clear that more structural variety is possible in simple inorganic molybdenum systems than had heretofore been admitted. Recognition of this diversity may be crucial in the quest to determine the nature of the biological molybdenum sites.
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Thus I1 is a common product from two apparently different reaction pathways. The 13C N M R of a 15% 13CO-enriched sample of I1 shows five resonances at the low temperature limit (-24 "C) in the carbonyl region (Figure I ) . This suggests that the cluster has the same overall summetry as I.5 The lowest energy exchange process averages resonances a and b at +2 "C and arises from axial-radial exchange at the unique ruthenium atom, Ru( 1 ) (AG* = 12.7 f 0.5 kcal/mol).6 At +25 OC resonances c, d , and e have coalesced while the resonance arising from the average of ( a b ) remains relatively sharp. This second stage of the CO-scrambling process arises from localized axial-radial exchange at Ru(2) and Ru(3) (AG* = 14.8 f 0.5 kcal/mol).6 At $60 O C resonances ( a b ) and (c d e ) coalesce to a single broad resonance, This third stage of the exchange probably arises from the onset of intermetallic CO scrambling via CO-bridging intermediates in a typical Cotton-type CO-
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