Organometallics 2010, 29, 2631–2633 DOI: 10.1021/om100142d
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Addition of Dimethyl Acetylenedicarboxylate to the [WSe4]2- Anion Wai-Hang Chiu,† Qian-Feng Zhang,‡ Ian D. Williams,† and Wa-Hung Leung*,† †
Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, People’s Republic of China, and ‡Institute of Molecular Engineering and Applied Chemistry, Anhui University of Technology, Ma’anshan, Anhui 243002, People’s Republic of China Received February 23, 2010 Summary: Treatment of [Et4N]2[WSe4] with dimethyl acetylenedicarboxylate (DMA) afforded the alkyne diselenolene complex [Et4N]2[W(η2-DMA){Se2C2(CO2Me)2}2] (1) along with a minor product, [Et4N]2[W(Se){Se2C2(CO2Me)2}2] (2). The crystal structures of both complexes have been determined by X-ray crystallography. Complex 1 is best described as a metallacyclopropene with two ene-diselenolate ligands.
Introduction Metal dithiolene complexes are of interest due to their interesting redox, optical, and catalytic properties and their important roles in bioinorganic catalysis.1-3 While bis(dithiolene) complexes have been extensively studied and used as building blocks for advanced materials,2,4 the selenium analogues (diselenolenes)5,6 have received less attention, due in part to the lack of general synthetic methods for the ligands and/or their complexes. One attractive synthetic route to metal dithiolenes is the [2 þ 3] cycloaddition of the SdMdS moiety with alkynes.7 Of note is the fact that [ReS4]reacts with a variety of unsaturated substrates, including alkynes, alkenes, nitriles, and isonitriles, to give the corresponding cycloaddition products.7,8 By comparison, [MS4]2(M = Mo, W) species are less reactive and can undergo cycloaddition with activated alkynes such as DMA only. For example, treatment of [Et4N]2[WS4] with DMA afforded a *To whom correspondence should be addressed. E-mail: chleung@ ust.hk. (1) (a) McCleverty, J. A. Prog. Inorg. Chem. 1968, 10, 49. (b) Burns, R. P.; Mcauliffe, C. A. Adv. Inorg. Chem. Radiochem. 1979, 22, 303. (c) Prog. Inorg. Chem. 2004, 52, various chapters. (2) Robertson, N.; Cronin, L. Coord. Chem. Rev. 2002, 227, 93. (3) Pilato, R. S.; Stiefel, E. I. In Bioinorganic Catalysis, 2nd ed.; Reedijk, J., Bouwman, E., Eds.; Marcel Dekker: New York, 1999; p 81. (4) Tanaka, H.; Okano, Y.; Kobayashi, H.; Suzuki, W.; Kobayashi, A. Science 2001, 291, 285. (5) (a) Morgado, J.; Santos, I. C.; Duarte, M. T.; Alcacer, L.; Almeida, M. Chem. Commun. 1996, 1837. (b) McLauchlan, C. C.; Robowski, S. D.; Ibers, J. A. Inorg. Chem. 2001, 40, 1372. (c) Ribas, X.; Dias, J.; Morgado, J.; Wurst, K.; Santos, I. C.; Almeida, M.; Vidal-Gancedo, J.; Veciana, J.; Rovira, C. Inorg. Chem. 2004, 43, 3631. (d) Ribas, X.; Dias, J. C.; Morgado, J.; Wurst, K.; Almeida, M.; Parella, T.; Veciana, J.; Rovira, C. Angew. Chem., Int. Ed. 2004, 43, 4049. (6) Ansari, M. A.; Mahler, C. H.; lbers, J. A. Inorg. Chem. 1989, 28, 2669. (7) Rauchfuss, T. B. Prog. Inorg. Chem. 2004, 52, 1. (8) (a) Goodman, J. T.; Inomata, S.; Rauchfuss, T. B. J. Am. Chem. Soc. 1996, 118, 11674. (b) Goodman, J. T.; Rauchfuss, T. B. Angew. Chem., Int. Ed. Engl. 1997, 36, 2083. (c) Goodman, J. T.; Rauchfuss, T. B. J. Am. Chem. Soc. 1999, 121, 5017. (d) Dopke, J. A.; Wilson, S. R.; Rauchfuss, T. B. Inorg. Chem. 2000, 39, 5014. (e) Schwarz, D. E.; Rauchfuss, T. B. Chem. Commun. 2000, 1123. (9) Mallard, A.; Simonnet-Jegat, C.; Lavanant, H.; Marrot, J.; Secheresse, F. Transition Met. Chem. 2008, 33, 143. r 2010 American Chemical Society
mixture of [Et4N]2[W2(μ-S)2{η2-S2C2(CO2Me)2}4], [Et4N]2[W2(S)2(μ-S)2{η2-S2C2(CO2Me)2}2], and [Et4N]2[W(O){η2S2C2(CO2Me)2}2].9 Dithiolene complexes have also been synthesized from reactions of transition-metal polysulfide complexes with alkynes.7,10,11 Rauchfuss and co-workers demonstrated that the reaction of 1,4-[(η5-C5H4R)2Ti]2S4 with DMA initially afforded a vinyl disulfide metallacycle that rearranged intramolecularly to the diothiolene complex.10 Although the addition of DMA to the tungsten polyselenides [WSe9]- and [W2Se10]2- to give [W{Se2C2(CO2Me)2}3]2- and [W2(Se)2{Se2C2(CO2Me)2}2]2-, respectively, has been reported by Ibers,6 to our knowledge, the cycloaddition of tetraselenometalates with alkynes has not been explored. Herein, we describe the [2 þ 3] cycloaddition of [WSe4]2- with DMA, which results in the formation of a W(IV) η2-alkyne bis(diselenolene) complex.
Results and Discussion Syntheses. Treatment of [Et4N]2[WSe4] in acetonitrile with 2 equiv of DMA at 0 °C resulted in an immediate change of color from purple to orange. Recrystallization from aceonitrile/Et2O at 0 °C for 2 days afforded orange-red crystals identified as [Et4N]2[W(η2-DMA){Se2C2(CO2Me)2}2] (1) along with a minor product, [Et4N]2[W(Se){Se2C2(CO2Me)2}2] (2) (Scheme 1). Although the cycloaddition of [MS4]n(M = Re, n = 1; M = Mo, W, n = 2; M = V, n = 3) with alkynes to give dithiolene complexes is well documented,7 to our knowledge, this is the first report of such a reaction for a tetraselenometalate anion. The formation of an η2-alkyne complex from [MS4]n- and alkyne is also unprecedented. It should, however, be noted that metallacyclic vinyl disulfide complexes have been isolated from reactions of metal di- and polysulfides with DMA.10,12 No reaction was found between [WSe4]2- and unactivated alkynes such as diphenylacetylene (10) (a) Bolinger, C. M.; Rauchfuss, T. B.; Rheingold, A. L. Organometallics 1982, 1, 1551. (b) Bolinger, C. M.; Rauchfuss, T. B.; Rheingold, A. L. J. Am. Chem. Soc. 1983, 105, 6321. (c) Giolando, D. M.; Rauchfuss, T. B.; Rheingold, A. L.; Wilson, S. R. Organometallics 1987, 6, 667. (d) Rauchfuss, T. B.; Rogers, D. P. S.; Wilson, S. R. J. Am. Chem. Soc. 1986, 108, 3114. (11) (a) Draganjac, M.; Coucouvanis, D. J. Am. Chem. Soc. 1983, 105, 140. (b) Rakowski DuBois, M.; DuBois, D. L.; VanDerveer, M. C.; Haltiwanger, R. C. Inorg. Chem. 1981, 20, 3064. (c) Rajan, O. A.; McKenna, M.; Noordik, J.; Haltiwanger, R. C.; Rakowski DuBois, M. Organometallics 1984, 3, 831. (d) Seyferth, D.; Henderson, R. S. J. Organomet. Chem. 1979, 182, C39. (e) Weberg, R.; Haltiwanger, R. C.; Rakowski DuBois, M. Organometallics 1985, 4, 131. (f) Pilato, R. S.; Eriksen, K. A.; Greaney, M. A.; Stiefel, E. I.; Goswami, S.; Kilpatrick, L.; Spiro, T. G.; Taylor, E. C.; Rheingold, A. L. J. Am. Chem. Soc. 1991, 113, 9372. (12) Halbert, T. R.; Pan, W.-H.; Stiefel, E. I. J. Am. Chem. Soc. 1983, 105, 5476. Published on Web 05/11/2010
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Scheme 1
and bis(trimethylsilyl)acetylene. The mechanism by which 2 is formed is not clear but probably involves an unsaturated “[W{Se2C2(CO2Me)2}2]2-” intermediate. Rauchfuss and coworkers reported the isolation of Re(S)(S2C2R2)2 by reaction of [ReS4]- with C2R2 in the presence of S8.8a However, we found that the addition of elemental selenium has no influence on the yield of 2. It is also unlikely that 2 was derived from 1, because no reaction was found between 1 and elemental selenium. Rauchfuss and co-workers reported that the use of a supplemental oxidant such as 4-methylmorpholine Noxide (NMO) and elemental sulfur facilitates the cycloaddition of [ReS4]- with alkynes and alkenes.8a,c However, the interaction of [WSe4]2- with DMA in the presence of NMO or S8 resulted in intractable materials. In the formation of 1, the highly electrophilic DMA serves as a supplementary oxidant that facilitates the [2 þ 3] cycloaddition. Spectroscopy. The electronic spectrum of 1 in acetonitrile showed broad absorptions at 350-450 nm that are tentatively assigned to ligand-to-metal charge-transfer (pπ(Se) f dπ(W)) transitions. Similar absorption bands have been found for [W{Se2C2(CO2Me)2}3]2-.6 The IR spectrum of 1 displayed the νCC band for the alkyne ligand at 1671 cm-1, which is similar to those of W(II) complexes with fourelectron alkyne ligands13 but considerably lower than that in W(CO)2(dppe)(η2-DMA)2 (1895 cm-1) (dppe = Ph2PCH2CH2PPh2), in which DMA is a two-electron ligand.14 The rather low C-C stretching frequency for 1 is indicative of strong metalto-alkyne back-bonding and CdC double-bond character for the alkyne ligand, consistent with the solid-state structure (vide infra). The 77Se NMR spectrum of 1 showed the resonance due to the diselenolene ligands at δ 676.78, which is more upfield than that for [W{Se2C2(CO2Me)2}3]2- (δ 839). The Se resonance for the diselenolene ligands of 2 was observed at a more downfield position: δ 730. Crystal Structures. Figure 1 shows the molecular structure of the complex anion in 1. The geometry around W in 1 is distorted trigonal prismatic, with one carbon and one selenium from each diselenolene ligand on a trigonal face. The W-Se distances in 1 are in the range 2.458(5)-2.544 (5) A˚, which compare well with those in [W{Se2C2(CO2Me)2}3]2(average 2.50(1) A˚).6 Similar to the case for [W{Se2C2(CO2Me)2}3]2-, one W-Se bond in each diselenolene ligand is slightly longer (0.02 and 0.045 A˚, respectively) than the other. The C-C distance of the DMA ligand in 1 is rather long (1.350(8) A˚), consistent with formulation of a CdC double bond. The C-C distance in 1 is within the range expected for four-electron alkyne ligands13 but considerably (13) (a) Templeton, J. L. Prog. Inorg. Chem. 1989, 29, 1. (b) Baker, P. K. Prog. Inorg. Chem. 1996, 40, 45. (14) Birdwhistell, K. R.; Tonker, T. L.; Templeton, J. L. J. Am. Chem. Soc. 1987, 109, 1401.
Figure 1. Molecular structure of the dianion [W(η2-DMA){Se2C2(CO2Me)2}2]2- in 1. Hydrogen atoms are omitted for clarity. The ellipsoids are drawn at the 30% probability level. Selected bond lengths (A˚) and angles (deg): W(1)-C(2) = 2.006(5), W(1)C(3) = 2.021(5), C(2)-C(3) = 1.350(8), W(1)-Se(1) = 2.5444(5), W(1)-Se(2) = 2.4619(5), W(1)-Se(3) = 2.4582(5), W(1)-Se(4) = 2.5433(5), Se(1)-C(12) = 1.906(5), Se(2)-C(13) = 1.924(5), C(12)-C(13) = 1.348(7), Se(3)-C(22) = 1.935(5), Se(4)-C(23) = 1.890(5), C(22)-C(23) = 1.339(7); C(2)-W(1)-C(3) = 39.2(2), C(3)-C(2)-C(1) = 135.7(4), C(2)-C(3)-C(4) = 134.4(4), Se(2)W(1)-Se(1) = 83.655(17), Se(3)-W(1)-Se(4) = 83.687(17).
longer than those for two-electron alkyne complexes such as W(CO)2(dppe)(η2-DMA)2 (1.292(4) and 1.303(4) A˚).14 The long alkyne C-C distance and small C-C-CO2Me bond angles (135.7(4) and 134.4(4)°) suggest that 1 is best described as a W(IV) metallacyclopropene. Figure 2 shows the structure of the complex anion in 2. The geometry around W in 2 is pseudo square pyramidal with the selenide group at the apical position. The W atom is displaced above the Se4 mean plane by ca. 0.80 A˚. The WdSe bond distance of 2.2893(12) A˚ is typical for a terminal WdSe bond.15 The W-Se bond distances for the diselenolene ligands of 2 (average 2.47 A˚) are slightly shorter than those in 1. The difference in W-Se bond lengths for each diselenolene ligand in 2 (0.018 and 0.02 A˚) is less than that in 1. In summary, we have demonstrated that, similar to the case for [MS4]n- (M = Re, n = 1; M = Mo, W, n = 2; M = V, n = 3), the [WSe4]2- anion undergoes [2 þ 3] cycloaddition with DMA to give diselenolene complexes. Unlike the sulfido analogue, [WSe4]2- reacts with DMA to afford the η2-alkyne bis(selenolene) complex 1. X-ray and IR data revealed that there is substantial metal-to-alkyne back-bonding in 1 and the complex is best described as a W(IV) metallacyclopropene.
Experimental Section General Considerations. All manipulations were carried out under nitrogen by standard Schlenk techniques. Solvents were purified, distilled, and degassed prior to use. NMR spectra were recorded on a Bruker AV 400 MHz NMR spectrometer operating at 400.13 and 76.4 MHz for 1H and 77Se, respectively. Chemical shifts (δ, ppm) were reported with reference to SiMe4 (1H) and Se2Ph2 (77Se). Infrared spectra were recorded on a (15) Zhang, Q.-F.; Leung, W.-H.; Xin, X. Coord. Chem. Rev. 2002, 224, 35.
Note
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Table 1. Crystallographic Data and Experimental Details for [Et4N]2[W(η2-DMA){Se2C2(CO2Me)2}2] 3 1/2H2O (1 3 1/2H2O) and [Et4N]2[W(Se){Se2C2(CO2Me)2}2] (2) 1 3 1/2H2O
Figure 2. Molecular structure of the dianion [W(Se){Se2C2(CO2Me)2}2]2- in 2. Hydrogen atoms are omitted for clarity. The ellipsoids are drawn at the 30% probability level. Selected bond lengths (A˚) and angles (deg): W(1)-Se(5) = 2.2893(12), W(1)Se(1) = 2.4665(12), W(1)-Se(2) = 2.4659(12), W(1)-Se(3) = 2.4789(13), W(1)-Se(4) = 2.4601(13), Se(1)-C(3) = 1.926(9), Se(2)-C(2) = 1.905(10), Se(3)-C(7) = 1.952(11), Se(4)-C(6) = 1.932(9), C(2)-C(3) = 1.364(12), C(6)-C(7) = 1.286(14); Se(1)W(1)-Se(2) = 84.52(4), Se(4)-W(1)-Se(3) = 83.88(4). Perkin-Elmer 16 PC FT-IR spectrophotometer. Elemental analyses were performed by Medac Ltd., Surrey, U.K. [Et4N]2[WSe4] was prepared by a modification of the literature method.16 Preparations of [Et4N]2[W(η2-DMA){Se2C2(CO2Me)2}2] (1) and [Et4N]2[W(Se){Se2C2(CO2Me)2}2] (2). To a solution of [Et4N]2[WSe4] (59 mg, 0.078 mmol) in acetonitrile (10 mL) was added DMA (29 μL, 0.24 mmol) at 0 °C. The pink solution turned orange-red immediately and was further stirred for 10 min. The solvent was pumped off, and the residue was washed with Et2O (5 mL 2) and then extracted into MeCN (5 mL 2). The extract was layered with E2O (5 mL) at -4 °C. After 2 days, the red blocks and orange needles that formed were collected and separated manually for X-ray analyses. 1: yield 53.2 mg (57%). 1H NMR (CD3CN): δ 1.11 (t, 24H, CH3), 1.51 (br, 2H, H2O), 1.98 (s, 1H, CH3CN), 3.00 (q, 16H, CH2), 3.60 (s, 6H, CH3), 3.69 (s, 12H, CH3). 77Se NMR (CD3CN): δ 676.78 (s). IR (KBr; cm-l): 1710, 1689 (νCO), 1671 (νCC). UV/vis (CH3CN; λmax/nm (ε /M-1 cm-1)): 272 (21 690), 372 (8700), 408 (7720). Anal. Calcd for C34H58N2O12Se4W 3 H2O 3 1/4CH3CN: C, 34.11; H, 5.04; N, 2.59. Found: C, 33.73; H, 4.83; N, 2.91. 2: the isolated yield of this compound ( 2σ(Ι)) R1, wR2 (all data) 0.0502, 0.1246 0.0620, 0.0918 P P a 1/2 b GOF - |Fc|)2/(Nobs - N (|Fo| param)] . R1 = ( P =c [ w(|Fo|P 2 2 P 2 2 1/2 |Fc|)/ |Fo|. wR2 = [ w (|Fo| - |Fc|) / w |Fo| ] .
2CH3CN: C, 33.79; H, 5.36; N, 4.38. Found: C, 34.11; H, 5.58; N, 4.29. X-ray Crystallography. Crystallographic data and experimental details for 1 and 2 are summarized in Table 1. Intensity data were collected on a Bruker SMART APEX 1000 CCD diffractometer using graphite-monochromated Mo KR radiation (λ = 0.710 73 A˚). The data were corrected for absorption using the program SADABS.17 Structures were solved by direct methods and refined by full-matrix least squares on F2 using the SHELXTL software package.18 The largest peak in the final difference map is in the vicinity of the tungsten atom.
Acknowledgment. Financial support from the Hong Kong Research Grants Council (Project No. 601506) is gratefully acknowledged. Q.-F.Z. thanks the Natural Science Foundation of China (No. 20771003) for support. We thank Dr. Herman H. Y. Sung for solving the crystal structures and the reviewers for useful comments. Supporting Information Available: CIF files giving crystal data, final atomic coordinates, anisotropic thermal parameters, and complete bond lengths and angles for complexes 1 3 1/2H2O and 2. This material is available free of charge via the Internet at http://pubs.acs.org. (18) Sheldrick, G. M. SHELXTL-Plus V5.1 Software Reference Manual; Bruker AXS: Madison, WI, 1997.
