3623
Organometallics 1995, 14, 3623-3624
Heterobimetallic Complexes Bridged by a Single 4e Sulfur Ligand: Addition of M'(C0)s (M' = Cr, Mo, W)to the Ta=S Bond of (t=BuCgH4)2Ta(S)H Henri Brunner,+ Sylvine Challet,$Marek M. Kubicki,t Jean-Claude Leblanc,$ Claude Moi'se,*$$Florence Volpato,$and Joachim Wachter*?t Laboratoire de Synthbe et d'Electrosynthlse Organomitalliques (URA1685), Universit6 de Bourgogne, F-21100 DQon, France, and Institut f i r Anorganische Chemie der Universitat Regensburg, 0-93040 Regensburg, Germany Received June 19, 1995@ Chart 1
Summary: Reaction of Cp'ZTa(=S)H with M'(C0)dTHF) (M' = Cr, Mo, W)gives rise to the formation of adducts i n which the M'(co)5 fragments are coordinated to the Ta-S double bond as established by means of ' H N M R and, i n the case of M' = W, by X-ray diffraction data. There is an enormous variety of transition metal complexes with monosulfur bridges ranging from dinuclear molecules to cluster compounds.' It is striking, however, that dinuclear complexes containing only one single sulfur bridge without further support are comparatively rare. Three different bonding modes A-C have been established in which the sulfur either acts as 2 (type A),24 (B),3or 6 (Q4electron donor (Chart 1). Only a few heterobimetallic complexes comprising a M-S-M linkage have been structurally characterized thus far, and they all belong t o type A.5 This work reports on a new synthetic strategy employing the coordinating ability of a sulfur lone pair of a metalsulfur double bond toward coordinatively unsatured transition metal carbonyl substrates. The coordination of M(C0)5 fragments onto pz-, pg-, and even p4-S ligands has already been successfully attempted,6 but the coordination of metal carbonyl fragments t o the sulfur lone pair electrons of a metal-sulfur double bond is still unexplored. Appropriate substrates comprising a M=S bond are metallocene sulfides of the early transition element^.^,^ Universitat Regensburg. Universite de Bourgogne. Abstract published in Advance ACS Abstracts, July 15, 1995. (1)Recent examples are summarized in the following reviews: Pasynskii, A. A.; Eremenko, I. L. Sou. Sci. Reu. B . Chem. 1987, 10, 443. Fenske, D.; Ohmer, J.; Hachgenei, J.; Merzweiler, K. Angew. Chem., Int. Ed. Engl. 1988,27, 1277. Wachter, J.Angew. Chem., Int. Ed. Engl. 1989,28,1613. Lee, S. C.; Holm, R. H. Angew. Chem., Int. Ed. Engl. 1990,29, 840. Shibahara, T. Coord. Chem. Rev. 1993,123, 73. (2) El-Hinnawi, M. A,; Aruffo, A. A,; Santarsiero, B. D.; McAlister, D. R.; Schomaker, V. Inorg. Chem. 1983,22, 1585. (3) Beuter, G.; Drobnik, S.; Lorenz, I.-P.; Lubik, A. Chem. Ber. 1992, 125,2363. (4) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1986,25,56 and literature cited therein. Jasim, K. S.; Chieh, C.; Mak, T. C. W. Angew. Chem., Int. Ed. Engl. 1986,25, 749. Brennan, J. G.; Andersen, R. A.; Zalkin, A. Inorg. Chem. 1986, 25, 1761. Evans, W. J . ; Rabe, G. W.; Ziller, J . W.; Doedens, R. J. Inorg. Chem. 1994, 33, 2719. (5) Kovacs, J. A,; Bergman, R. G. J . A m . Chem. SOC.1989,111,1131. Massa, M. A.; Rauchfuss, T. B.; Wilson, S. R. Inorg. Chem. 1991,30, 4667. (6) Pasynskii, A. A.; Eremenko, I. L.; Rakitin, Y. V.; Orazsakhatov, B.; Novotortsev, V. M.; Ellert, 0. G.; Kalinnikov, V. T.; Aleksandrov, G. G.; Struchkov, Y. T. J . Organomet. Chem. 1981,210,377. Adams, R. D.; Babin, J . E.; Wang, J.-C.; Wu, W. Inorg. Chem. 1989,28, 703. Adams, R. D.; Babin, J . E.; Wang, J.-G. Polyhedron 1989, 8, 2351. (7) Carney, M. J.; Walsh, P. J.; Hollander, F. J.; Bergman, R. G. Organometallics 1992, 11, 761. Howard, W. A,; Waters, M.; Parkin, G. J . Organomet. Chem. 1994,472, C1. +
@
type B
type C
Among them Cp'zTa(S)H (1)is easily accessible by sulfur abstraction from Cp'zTa(Sz)H.8 The reaction of 1 with M(C0)aTHF ( M = Cr, Mo, W) in THF gives red adductsg (eq 1) the composition of Cp'2TaeS
H'
+
M'(C0)sTHF
-
1
2 (Cp'=t-BuC,H,; M=Cr: a; M'=Mo: b; M'=W: c)
(1) which has been confirmed by analytical (2a,c) and spectroscopic means (2a-c).1°Complex 2b is not sufficiently stable to give a correct analysis. The question as t o whether the hydride or the sulfide ligand is involved as a bridging ligand is answered by the lH NMR spectra: in all three cases the very low TaH (8)(a) Bach, H.-J.; Brunner, H.; Wachter, J.; Kubicki, M. M.; Leblanc, J.-C.; Moi'se, C.; Volpatu, F.; Nuber, B.; Ziegler, M. L. Organometallics 1992,11, 1403. (b) Nelson, J . E.; Parkin, G.; Bercaw, J. E. Organometallics 1992, 11, 2181. (c) Brunner, H.; Kubicki, M. M.; Leblanc, J.-C.; MoYse, C.; Volpato, F.; Wachter, J . J . Chem. Soc., Chem. Commun. 1993,851. (9) Preparation of 2a-c: A mixture of 200 mg (0.44 mmol) of 1, a slight excess (20%) of the appropriate M'(CO)c(THF) complex, and 30 mL of THF were stirred at room temperature for 30 min while the color of the solution turned from pink to dark red. After evaporation of the solvent under reduced pressure the solid residue was chromatographed on silanized silica gel with toluene as eluant and subsequently recrystallized from 1:l toluendpentane to give darkred crystals of Cp'zTa[=S-M'(C0)51H (2). (10) Spectroscopic and analytical data for 2a are as follows. 'H NMR (C6D6): 6 6.64 (s, 1 H, T m ; 5.60 (m, 2H), 5.31 (m, 2H), 5.05 (m, 2H), 4.40 (m, 2H) (Cfld); 1.11( 6 , 18H, C(CH313). IR (CsI, cm-'1: 360 (m, V T ~ - S ) . IR (THF, cm-l): 2054 (s), 1936 (w), 1924 (sh), 1892 (m) ( V C O ) . Anal. Calcd for C23H2705CrSTa: C, 42.6; H, 4.2; mol. wt, 648.5. Found: C, 41.8; H, 4.1; mol wt, 648.1 (FD MS). Spectroscopic data for 2b are as follows. 1H NMR (C6D6): 6 6.83 (s, lH,TaH);5.57 (m, 2H), 5.27 (m, 2H), 5.13 (m, 2H), 4.45 (m, 2H) ( C a d ; 1.12 (s, 18H, C(CH3)3). IR (CsI, cm-1): 361 (m, V T ~ - S ) . IR (THF, cm-'): 2065 (SI, 1939 (w), 1930 (sh), 1889 (m) ( Y C O ) . Spectroscopic and analytical data for 2c are as follows. 1H NMR (CsD6): 6 6.79 (s, l H , TaH); 5.56 (m, 2H), 5.24 (m, 2H), 5.06 (m, 2H), 4.38 (m, 2H) (Cfl4); 1.09 (s, 18H, C(CH3)3). IR (CsI, cm-1): 366 (m, V T ~ - S ) . IR (THF, cm-l): 2061 (s), 1930 (w), 1885 (m) (VCO). Anal. Calcd for C23H2705WSTa: C, 35.4; H, 3.5; mol. wt, 780.3. Found: C, 34.4; H, 3.5; mol. wt, 779.9 (FD MS). (11)Leblanc, J . C.; Reynoud, J . F.; MoYse, C. J . Organomet. Chem. 1963,244, C24.
0276-7333/95/2314-3623$Q9.QQ/Q0 1995 American Chemical Society
Communications
3624 Organometallics, Vol. 14,No. 8, 1995 Scheme 1 C05
01
Figure 1. ORTEP drawing of (t-BuC5H4hTa[=S-W(CO)b]H(2c). Selected distances (A) and angles ("1: Ta-S = 2.274(5),Ta-H = 1.74 (calcd),W-S = 2.554(4);W-STa = 135.9(2),CP1-Ta-CP2 = 134.0. resonance at 6 = 7.10 is only shifted by about 0.4 ppm to higher field, whereas the corresponding resonance in [(C5H5)2Ta(CO)OL-H)lCr(CO)5is shifted by ca. 12 ppm to higher field.ll An X-ray diffraction analysis of Cp'2Ta[=S-W(C0)51H (2c)12confirms the bridging nature of sulfur (Figure 1). The Ta-S-W angle (135.9") indicates an approximate sp2 hybridization of the sulfur atom. A relatively short Ta-S distance (2.274 A) which is only slightly longer than those reported for TaSCl3(PhSCH2CH2SPh) (2.204 A) and TaS(SzCNEt& (2.181 All3 is consistent with a formal Ta=S double bond. The hydride ligand could not be found in the final difference Fourier map and has been placed in calculated position.14 (12)X-ray structure analysis of 2c: A red crystal having the approximate dimensions 0.2 x 0.1 x 0.1 mm was used for unit cell measurements and intensity data collection, carried out at 296 K on an Enraf-Nonius CAD4 diffractometer with Mo K a radiation (1 = 0.710 73 A). All calculations have been carried out by using the EnrafNonius Molen library. The structure was solved and refined by standard methods. 2c: monoclinic, space group P21/n (No. 14), a = 12.238(2)A,b = 18.258(3)A,c = 12.831(2)A, = 116.23(1)"V = 2572.0 A3,deale= 2.015 g . ~ m - 2~ ,= 4, and p = 88.75 cm-l. An empirical absorption correction (v scan, absmln= 77.9341, abs" = 99.7128)was applied. All non-hydrogen atoms were refined with anisotropic temperature factors, and the hydrogen atoms were placed in calculated positions. These last atoms were ridden on the atoms bearing them and included in the final calculations with Bise fmed at the values equal to 1.38, for the corresponding carbon atoms. Full-matrix least-squares refinement based on 1610 unique reflections with I > ldl)converged at R = 0.030. Full details are given in the supporting information. (13)Drew, M. G. B.; Rice, D. A.; Williams, D. M. J . Chem. Soc., Dalton Trans. 1984, 845. Peterson, E. J.; von Dreele, R. B.; Brown, T. M. Inorg. Chem. 1978,17,1410. A discussion of short Ta-S bonds is given in: Tatsumi, K.; Inoue, Y.; Kawaguchi, H.; Kohsaka, M.; Nakamura, A.; Cramer, R. E.; VanDoorne, W.; Taogoshi, G. J.; Richmann, P. N. Organometallics 1993, 12, 352. (14)The coordinates of the hydride ligand, needed for EHMO calculations, are proposed on the basis of typical geometries observed in bent tantalocenes CpzTaXz by assuming the Ta-H bond length equal to 1.74 A,the S-Ta-H angle of go", and the orthogonality of the CplTaCpz and STaH planes. (15) Hoffmann, R. J . Chem. Phys. 1963, 39, 1397. Mealli, C.; Proserpio, D. M. J . Chem. Educ. 1990, 67, 399. (16) Lauher, J. W.; Hoffmann, R. J . Am. Chem. SOC.1976,98, 1729. (17)The atomic parameters H,,used in this study were those contained in the DATA file of CACAO. Interatomic distances and bond angles were taken from the structure of 2c reported here.
EHMO calculation^^^ on a model (CbH&Ta[=S-W(C0)5lH show that the Ta=S rc orbital is localized in the HTaS plane which corresponds to an usual donor interaction of the p atomic orbital of sulfur into the empty nonbonding orbital (la1 in the Lauher-Hoffman model)16of Ta(V). For a sp2-hybridizedsulfur atom the ideal value of HTaSPTaSW dihedral angle should be equal to 90". Such a value should lead to strong steric repulsions between one Cp' ligand and the w(co)5 fragment. Thus, the observed value is smaller (79.5") and the largely opened TaSW angle (135.9') confirms the pregence of steric intramolecular repulsions. However, the molecular geometry of 2c found in the solid state does not correspond to the structure expected on the basis of 'H NMR spectroscopy. The spectra recorded from room temperature to -75 'C (in acetone-&) exibit one resonance for the t-Bu substituent and four signals for the v5-C5H4 protons. Such a pattern is consistent with a magnetic equivalence of both Cp' ligands and a symmetrical orientation of the w(co)~, fragment with respect to these ligands. In order to clarify this apparent contradiction, additional EHMO calculations have been carried in a way that two dihedral angles a (HTaSPTaSW) and /3 (TaSW/SWC02) (Scheme 1) have been varied from 0 (endo) to 180" (exo geometry) and from 0 to go', respectively. The resulting minima of total energy are obtained for values of a and /3 close to 60 and 30", respectively. These results are in good agreement with the X-ray data: a (HTaSPTaSW)= 79.5" and /3 (TaSW/ SWC2) = 36.6". Finally, it is important to note that the minimum of total energy for the conformation corresponding to the symmetrical structure suggested by lH NMR (a = 0") is only 0.2 eV ( e l 9 kJ/mol) higher than that for the stable conformation (a = 60"). This means that the rotation of the W(C0)s fragment around the Ta=S bond may easily occur in solution. In conclusion we have shown that the addition of M (Cola fragments to the Ta=S bond gives heterobimetallic compounds comprising an unsupported 4e sulfur bridge. 'H NMR investigations in solution and EHMO calculations are in agreement with a rotation around the Ta=S bond the energy barrier of which is relatively low. Supporting Information Available: Plots of the total and minimal total energies of rotations around the Ta=S ( a ) and S-W (j3)bonds and tables of coordinates of non-hydrogen atoms, intramolecular distances and angles, hydrogen atom coordinates, isotropic and anisotropic temperature factors, and least-squares planes for 2c (8 pages). Ordering information is given on any current masthead page. OM9504680
