Organometallics 2009, 28, 3953–3956 DOI: 10.1021/om900244t
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Organoantimony(V) Oxido Cubane Cluster [(p-X-C6H4Sb)4(O)4(Ph2SiO2)4] (X = Cl, Br) Stabilized by Diphenyldisiloxides M. Santhana Raj Prabhu, Ananda Kumar Jami, and Viswanathan Baskar* School of Chemistry, University of Hyderabad, Hyderabad 500046, India Received March 31, 2009 Summary: Reaction of (p-halophenyl)stibonic acid with diphenylsilanediol (in ratio 1:1) in refluxing toluene for 6 h afforded colorless crystalline products in high yields. Singlecrystal X-ray structural elucidation reveals the formation of the products [(p-Cl-C6H4Sb)4(O)4(Ph2SiO2)4] (1) and [(p-Br-C6H4Sb)4(O)4(Ph2SiO2)4] (2), respectively. The clusters 1 and 2 were isostructural; the core consists of a distorted Sb4O4 cubane framework with the siloxides acting as bridging ligands across the antimony atoms present at alternate corners of the cube.
The study of multinuclear metal-oxo clusters has been fascinating chemists for some time now, owing to the possible generation of precursors for new materials possessing interesting physical and chemical properties.1 Since multinuclear clusters act as a bridge between molecular and solidstate chemistry, they help in understanding the size-dependent physical properties of materials.2 The cluster chemistry of main-group metals such as tin3 and bismuth4 linked through oxo/hydroxo bridges has been explored in detail; their solid-state and solution structures are well understood. In spite of the numerous applications of organoantimonate compounds in the field of catalysis5 and biology,6 the cluster chemistry of antimony(V) compounds bridged through oxo/ hydroxo linkages are few,7 though a large number of antimony-thio complexes have been known for years.8 Since the ability of phenylstibonic acid (PhSbO3H2) to self-condense and act as an inorganic cryptand incorporating d5 and d10 *To whom correspondence should be addressed. E-mail: vbsc@ uohyd.ernet.in. Tel: +91-40-66794825. Fax: +91-40-23012460. (1) (a) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101, 1629. (b) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O’Keeffe, :: M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319. (c) Muller, A.; :: Krikmeyer, E.; Bogge, H.; Schmidtmann, M.; Peters, F. Angew. Chem., Int. Ed. 1998, 37, 3360. (2) (a) Clusters and Colloids: From Theory to Applications; Schmidt, G., Ed.; VCH: Weinheim, Germany, 1994.(b) Physics and Chemistry of Metal Cluster Compounds; de Jongh, L. J., Ed.; Kluwer: Dordrecht, The Netherlands, 1994. (3) (a) Chandrasekhar, V.; Gopal, K.; Sasikumar, P.; Thirumoorthy, R. Coord. Chem. Rev. 2005, 249, 1745. (b) Chandrasekhar, V.; Nagendran, S.; Baskar, V. Coord. Chem. Rev. 2002, 235, 1. (c) Holmes, R. R. Acc. Chem. Res. 1989, 22, 190. (4) Mehring, M. Coord. Chem. Rev. 2007, 251, 974. (5) Huang, Y.-Z. Acc. Chem. Res. 1992, 25, 182. (6) Fujiwara, Y.; Mitani, M.; Yasuike, S.; Kurita, J.; Kaji, T. J. Health Sci. 2005, 51, 333. (7) (a) Southerington, I. G.; Begley, M. J.; Sowerby, D. B. J. Chem. Soc., Chem. Commun. 1991, 1555. (b) Said, M. A.; Swamy, K. C. K.; Babu, k.; Aparna, K.; Nethaji, M. J. Chem. Soc., Dalton Trans. 1995, 2151. (c) Said, M. A.; Swamy, K. C. K.; Poojary, D. M.; Clearfield, A.; Veith, M.; Huch, V. Inorg. Chem. 1996, 35, 3235. (d) Gibbons, M. N.; Sowerby, D. B. J. Chem. Soc., Dalton Trans. 1997, 2785. (8) Silvestru, C.; Haiduc, L. Coord. Chem. Rev. 1996, 147, 117. r 2009 American Chemical Society
metals in its cavity was reported recently,9 there has been an upsurge of interest in understanding the structure and reactivity patterns of organostibonic acids.10 In this regard, controlled hydrolysis of antimony dihalides and tetrahalides appended with sterically bulky organic substituents on antimony has been carried out, leading to the isolation of molecular arylstibonic acid, [2,6-Mes2C6H3Sb(O)(OH)2]2, and antimony-oxido clusters, wherein antimony is found in a mixed (III and V) state of oxidation.11 In a recent report,12 efforts to crystallize a sterically demanding stibine complex, 1,8-bis(R2-Sb) naphthalene (R = Me), has resulted in serendipitous hydrolysis of the organoantimony(III) compound, resulting in the isolation of a self-assembled tetranuclear cubane cluster in very low yields. Interestingly, phosphonate/antimonate-oxo clusters have also been synthesized, and their utility as proligands for assembling multinuclear cobalt clusters has been investigated.13 It is worth noting here that a bulky organic group appended on antimony and/or solvothermal synthesis have been employed to get around the poor solubility of the products obtained in the reactions involving stibonic acids, which in our view has hindered the progress of understanding the solid-state and solution chemistry associated with such systems. Further, reaction of hydrated Ph3SbCl2 with a cyclic phosphinic acid has been reported recently, resulting in the isolation of a dinuclear organoantimony cluster which on mild hydrolysis undergoes Sb-C bond cleavage, leading to the formation of a novel nonanuclear organostiboxane cage containing a Sb9O16 core.14 It should be mentioned here that antimony oxido clusters have been studied before in the gas phase or condensed phase by mass spectrometry,15 and it has been reported that at room temperature the stable solid phase of Sb2O3 is the cubic senarmontite which contains a Sb4O6 molecule,16 whereas the high-temperature orthorhombic phase valentinite has a polymeric sheet built up of (9) Baskar, V.; Shanmugam, M.; Helliwell, M.; Teat, S. J.; Winpenny, R. E. P. J. Am. Chem. Soc. 2007, 129, 3042. (10) Clark, C. J.; Nicholson, B. K.; Wright, C. E. Chem. Commun. 2009, 923. (11) (a) Beckmann, J.; Finke, P.; Hesse, M.; Wettig, B. Angew. Chem., Int. Ed. 2008, 47, 9982. (b) Beckmann, J.; Heek, T.; Takahashi, M. Organometallics 2007, 26, 3633. (c) Kelly, B. V.; Weintrob, E. C.; Buccella, D.; Tanski, J. M.; Parkin, G. Inorg. Chem. Commun. 2007, 10, 699. (d) Beckmann, J.; Hesse, M. Organometallics 2009, 28, 2345. (12) Jura, M.; Levason, W.; Reid, G.; Webster, M. Dalton Trans. 2008, 5774. (13) Ali, S.; Baskar, V.; Muryn, C. A.; Winpenny, R. E. P. Chem. Commun. 2008, 6375. (14) Chandrasekar, V.; Thirumoorthi, R. Organometallics 2009, 28, 2637. (15) Reddy, B. V.; Jena, P. Chem. Phys. Lett. 1998, 228, 253. (16) Reinicke, R. Z. Elektrochem. 1935, 41, 23.
Published on Web 05/28/2009
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Organometallics, Vol. 28, No. 13, 2009 Scheme 1
Prabhu et al. Table 1. Crystal Data and Structure Refinement Details for 1 and 2 1
eight-membered Sb4O4 rings.17 Generally in these clusters antimony atoms are present in both III and V states of oxidation, but at higher oxygen concentrations it has been shown that the formation of oxide clusters containing antimony atoms solely in the V state of oxidation is favored.18 Organosilanols, on the other hand, have been utilized for synthesizing metallosiloxane frameworks,19 and in particular the ability of di- and trisilanols to act as ligands toward main-group and transition metals has also been investigated in detail.20 Reaction of diphenylsilanediol with ECl3 (E = As, Sb) has resulted in the isolation of interesting arsenic(III) and antimony(III) bicyclic siloxane compounds.21 In this report, we present the synthesis and solid-state structure of [(p-X-C6H4Sb)4(O)4(Ph2SiO2)4] (X = Cl (1), Br (2)) obtained by refluxing a mixture of (p-halophenyl)stibonic acids with diphenylsilanediol in a 1:1 molar ratio in toluene (Scheme 1). The clusters (1 and 2) dissolved in a wide range of solvents such as dichloromethane, chloroform, toluene, and xylene. The products were characterized by standard spectroscopic and analytical techniques. The data of the crude products of 1 and 2 matched well with the data obtained from crystallized products. 1H NMR (in CDCl3 solution) for both 1 and 2 showed multiplets in the region 6.71-7.93 ppm, corresponding to the aromatic groups present. Closer examination of the spectra revealed some interesting features. The aromatic region (of the 1H NMR spectrum) of 1 shows two distinct groupings, the first one consisting of two closely spaced doublets (at 6.75 and 6.73 ppm) corresponding to the two sets of aromatic protons of the chlorophenyl group attached to antimony and the other consisting of two triplets (7.55 and 7.38 ppm) and a doublet (7.92 ppm) corresponding to the protons of phenyl groups attached to silicon atom. The 1H NMR spectrum of 2 also shows signals similar to those of (17) Buerger, M. J.; Hendricks, S. B. J. Phys. Chem. 1937, 5, 600. (18) Optiz-Coutureau, J.; Fielicke, A.; Kaiser, B.; Rademann, K. Phys. Chem. Chem. Phys. 2001, 3, 3034. (19) Murugavel, R.; Voigt, A.; Walawalkar, M. G.; Roesky, H. W. Chem. Rev. 1996, 96, 2205. :: (20) (a) Beckmann, J.; Jurkschat, K.; Schurmann, M.; Dakternieks, D.; Lim, A. E. K.; Lim, K. F. Organometallics 2001, 20, 5125. (b) Puff, :: :: H.; Bockmann, M. P.; Kok, T. R.; Schuh, W. J. Organomet. Chem. 1984, :: 268, 197. (c) Puff, H.; Kok, T. R.; Nauroth, P.; Schuh, W. J. Organomet. Chem. 1985, 281, 141. (d) Zherlitsyna, L.; Auner, N.; Bolte, M.; Pozdniakova, Y.; Shchegolikhina, O.; Lyssenko, K.; Pashchenko, V.; :: Wolf, B.; Lang, M.; Schutz, F.; Kollar, M.; Sauli, F.; Kopietz, P. Eur. J. Inorg. Chem. 2007, 4827. (e) Cornia, A.; Fabretti, A. C.; Gatteschi, D.; P alyi, G.; Rentschler, E.; Shchegolikhina, O. I.; Zhdanov, A. A. Inorg. Chem. 1995, 34, 5383. (21) (a) Ferguson, G.; O’Leary, B.; Spalding, T. R. Acta Crystallogr. 1995, C51, 2312. (b) Chamberland, B. L.; MacDiarmid, A. G. J. Am. Chem. Soc. 1960, 82, 4542. (c) Henglein, F. A.; Lang, R.; Scheinost, K. Makromol. Chem. 1956, 18, 102.
formula formula wt cryst syst cryst size, mm space group a, A˚ b, A˚ c, A˚ β, deg V, A˚3 Z Dcalcd, Mg m-3 T, K μ, mm-1 F(000) θ range, deg index range
C74H62Cl10O14Sb4Si4 2129.10 monoclinic 0.26 0.26 0.18 C2/c 24.828(13) 15.261(8) 24.943(13) 111.925(7) 8767(8) 4 1.613 298(2) 1.635 4192 1.66-26.05 -30 e h e 27 -16 e k e 18 -30 e l e 30 no. of rflns collected 33 146 completeness to θmax (%) 99.0 no. of indep rflns 8578 GOF 1.062 R1(F) (I > 2σ(I)) 0.0497 wR2 0.1572 large diff peak/hole, e A˚-3 1.720/-0.873
2 C72H76Br4O22Sb4Si4 2212.33 monoclinic 0.44 0.16 0.05 C2/c 24.949(4) 15.262(3) 24.924(4) 111.458(3) 8833(3) 4 1.664 298(2) 3.139 4336 1.60-25.11 -29 e h e 29 -18 e k e 18 -29 e l e 29 41 898 99.6 7857 1.087 0.0511 0.1691 1.684/-0.683
1, except that the two doublets due to the protons of the bromophenyl groups have slightly larger separation between them (Experimental Section). The 29Si NMR (in CDCl3 solution) spectrum showed a single signal at -29.5 ppm (for both 1 and 2), a small downfield shift compared to the 29 Si NMR of Ph2Si(OH)2 (-34.9 ppm). Single crystals of 1 and 2 were obtained from chloroform solution using hexane as the diffusing solvent over 1 week. The neutral clusters 1 and 2 crystallize in the monoclinic space group C2/c (Table 1). As 1 and 2 are isostructural, we consider the structure of 1 for discussion. The structure of 2 along with selected bond lengths (A˚) and bond angles (deg) is given in the Supporting Information. The solid-state structure of 1 reveals the formation of the tetranuclear organoantimony(V) oxido cluster [(p-Cl-C6H4Sb)4(O)4(Ph2SiO2)4], which contains a central Sb4O4 cubane encapsulated by four bridging diphenyldisiloxides (Figure 1). The spatial arrangement around each antimony atom is octahedral with O5C coordination: three coordinations from μ3-oxo groups of the cubane core, two from the oxygens of two neighboring bridging siloxide ligands, and one from the carbon of the chloro phenyl group. The Sb-O distances in the core fall in the range 2.066(9)-2.133(6) A˚, with the Sb-C distance being 2.102(1) A˚. The Sb-O-Sb angles in the cubane core fall in the range 100.98(14)-103.49(14)°. The Sb- - -Sb nonbonding distances are 3.241(2)-3.325(4) A˚. The metric parameters (Sb-O bond lengths, Sb-O-Sb bond angles, and the Sb—Sb nonbonding distances) are similar to those of the recently reported Sb4O4 cubane cluster.12 Four dianionic diphenyldisiloxides are present, wrapped around the central cubane core almost in an identical fashion. Of the six faces of the Sb4O4 cubane core, two opposite square faces are sterically encumbered by the presence of p-chlorophenyl groups on antimony; hence, the bifunctional diphenyldisiloxide ligands approach and bridge the antimony atoms through the remaining four square faces. It should be mentioned here that the condensation reactions of diphenylsilanediol with organotin or organotellurium oxides/hydroxides lead only to Lewis acid or Lewis base catalyzed self-condensation of
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Figure 1. ORTEP view of 1. Thermal ellipsoids have been set at the 30% probability level. Hydrogen atoms and solvent of crystallization have been omitted for clarity. Symmetry code used to generate equivalent atoms: 1-x, y, 1.5-z. Selected bond lengths (in A˚) and bond angles (in deg) in 1: Sb1-O1 = 2.121(3), Sb1-O2 = 2.066(9), Sb1-O3 = 1.935(5), Sb1-O2i = 2.133(6), Sb1-O6i = 1.927(5), Sb1i-C1i = 2.102(1), Sb2-O1 = 2.091(1), Sb2-O2 = 2.123(3), Sb2-O1i = 2.113(5), Sb2-O4 = 1.928(7), Sb2-O5 = 1.927 (3), Si1-O3 = 1.647(5), Si1-O4 = 1.627(5); O1-Sb1-O2i = 75.75(13), O1-Sb1-O2 = 77.31(13), O1-Sb1-O6 = 162.89(16), O1-Sb1-O3 = 91.85(17), O2-Sb1-O6 = 88.35(17), O2-Sb2-O1 = 88.38(16), Sb1-O1-Sb2 = 100.98(14), Sb2-O1-Sb2i = 103.49(14), Sb1-O2-Sb2 = 101.77(14), Sb1-O3-Si1 = 131.86(24), Sb2-O4-Si1 = 134.34(28), O3-Si1-O4 = 109.44(24).
diphenylsilanediols, yielding (Ph2SiO)3 or (Ph2SiO)4 as the major product.22 However, in the present case we do not encounter such self-condensed products of silanols, probably due to the less acidic nature of stibonic acid compared to that of organotin or organotellurium analogues. It is also possible that the formation of Sb-O-Si bonds is thermodynamically more favorable, leading to the isolation of a rather unexpected product. It is also of interest to note here that in the previously reported compound [(1,8-C10H6)(SbMe2)2]2O4, which contains a similar Sb4O4 cubane core,12 only two naphthalene dianions bridge the metal atoms in a mutually orthogonal fashion, but in 1 four [Ph2SiO2]2ligands bridge the central cubane core. The reason for this is that in the former case the orientation of the two alkyl groups on antimony atom is in such a way that the naphthalene can approach and bind to the metal centers only through two of the six square faces of the cube, whereas in 1, since a monoorgano antimony precursor is used, four of the six square faces of the self-assembled cubane core are accessible for the ligands to bind the metal centers. The Si-O bond (22) (a) Beckmann, J.; Jurkschat, K.; Rabe, S.; Schurmann, M.; Dakternieks, D.; Duthie, A. Organometallics 2000, 19, 3272. (b) Beckmann, J.; Bolsinger, J. Organometallics 2007, 26, 3601.
distances fall in the range 1.627(5)-1.647(5) A˚. The siliconbound O- - -Sb distance falls in the range 1.927(5)-1.935(5) A˚, which is considerably shorter than the Sb-O distances of the central cubane core. The Si-O-Sb angles vary between 131.86(24) and 134.34(24)°. The four tetrahedrally coordinated silicon atoms lie at the vertices of an almost square plane, with the Si- - -Si distances being 5.592(7)-5.767(7) A˚. The isolation of a Sb4O4 cubane cluster is significant, since cubane clusters are considered as important secondary building units (SBU’s) for synthesizing model compounds for zeolites.23 In summary, to the best of our knowledge, this is the first report of organoantimony(V) oxido siloxides containing a SbV-O-SiIV framework that has been structurally characterized. Silanols generally tend to form metallosiloxane frameworks on reaction with organometal precursors, but in the present case the silanol stabilizes the formation of a rare Sb4O4 cubane cluster. The use of silanetriols and other (23) (a) Boyle, T. J.; Pedrotty, D. M.; Alam, T. M.; Vick, S. C.; Rodriguez, M. A. Inorg. Chem. 2000, 39, 5133. (b) Thiele, K.; Gorls, H.; Seidel, W. Z. Anorg. Allg. Chem. 1998, 624, 1391. (c) Jackman, L. M.; Cizmeciyan, D.; Wiiliard, P. G.; Nichols, M. A. J. Am. Chem. Soc. 1993, 115, 6262. (d) MacDougall, D. J.; Morris, J. J.; Noll, B. C.; Henderson, K. W. Chem. Commun. 2004, 456.
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multifunctional ligands for assembling new organoantimony (V) oxido clusters is currently in progress.
Experimental Section Reagents and General Procedure. Diphenylsilanediol, solvents, and other common reagents were used as purchased from commercial sources. (p-Halophenyl)stibonic acids (halogen = Cl, Br) were synthesized using literature procedures.24 Instrumentation. Infrared spectra were recorded on a JASCO5300 FT-IR spectrometer as KBr pellets. The 1H, 13C, and 29Si solution NMR spectra were recorded on a Bruker DRX 400 instrument. Elemental analysis was performed on a Flash EA Series 1112 CHNS analyzer. Single-crystal X-ray data collection (for 1 and 2) was carried out at 298(2) K on a Bruker Smart Apex CCD area detector system (λ(Mo KR) = 0.710 73 A˚), with a graphite monochromotor. The data were reduced using SAINT PLUS, and the structures were solved using SHELXS-9725 and refined using SHELXL-97.26 All non-hydrogen atoms were refined anisotopically. Hydrogen atoms were not fixed for solvent molecules (chloroform in 1 and water molecules in 2). Synthesis. Synthesis of 1. Diphenylsilanediol (0.38 g, 1.76 mmol) and (p-chlorophenyl)stibonic acid (0.50 g, 1.76 mmol) were taken up in 50 mL of toluene, and the solution was refluxed for 6 h. A Dean-Stark apparatus was used to remove the water eliminated in the reaction as an azeotropic mixture. The clear solution that formed was cooled to room temperature, filtered to remove any unreacted starting materials present, and evaporated under reduced pressure to yield a colorless solid. Yield: 0.68 g (84%, based on the weight of (p-chlorophenyl)stibonic acid). Dec pt: 198-199 °C. Crystals (24) (a) Schmidt, H. Liebigs Ann. Chem. 1920, 421, 174. (b) Doak, G. O.; Steinman, H. G. J. Am. Chem. Soc. 1946, 68, 1987. (25) Sheldrick,G. M. SHELXS-97, Program for Crystal Structure :: :: Solution; University of Gottingen, Gottingen, Germany, 1997. (26) Sheldrick,G. M. SHELXL-97, Program for Crystal Structure :: :: Refinement; University of Gottingen, Gottingen, Germany, 1997.
Prabhu et al. suitable for single-crystal X-ray studies were grown from a chloroform solution by diffusion in hexane for 1 week. Anal. Calcd for C72H56O12Cl4Si4Sb4: C, 46.63; H, 3.04. Found: C, 46.68; H, 3.10. IR (cm-1, KBr pellet): 3069 m, 1591 s, 1570 s, 1477 s, 1429 s, 1385 s, 1263 s, 1126 w, 1091 w, 1024 w, 904 m, 808 s, 717 m, 698 s, 513 w, 484 w. 1H NMR in CDCl3: δ 7.92 (d, 16 H), 7.55 (t, 8 H), 7.38 (t, 16 H), 6.75 (d, 8 H), 6.73 (d, 8 H). 13C NMR in CDCl3: δ 139.63, 138.09, 135.20, 134.75, 133.83, 130.39, 128.58, 127.82. 29Si{1H} NMR in CDCl3: δ -29.5 ppm. Synthesis of 2. The procedure was similar to that of 1. The molar ratios and weights of the reactants used are as follows: diphenylsilanediol, 0.59 g and 2.74 mmol; (p-bromophenyl) stibonic acid, 0.90 g and 2.74 mmol. Yield: 0.98 g (70.2% based on (p-bromophenyl)stibonic acid). Dec pt: 199-200 °C. Anal. Calcd for C72H56O12Br4Si4Sb4: C, 42.55; H, 2.77. Found: C, 42.49; H, 2.75. IR (cm-1, KBr pellet): 3067 w, 2962 w, 1903 w, 1591 s, 1562 s, 1477 s, 1429 s, 1379 s, 1261 s, 1124 m, 1057 m, 1024 m, 941 m, 900 m, 804 s, 698 s, 511 m. 1H NMR in CDCl3: δ 7.88 (d, 16 H), 7.52 (t, 8 H), 7.34 (t, 16 H), 6.87 (d, 8 H), 6.65 (d, 8 H). 13C NMR in CDCl3: δ 140.24, 135.17, 134.74, 133.94, 131.51, 130.40, 127.83, 126.75. 29Si{1H} NMR in CDCl3: δ -29.5 ppm.
Acknowledgment. V.B. thanks Department of Science and Technology for financial assistance under the SERC-Fast Track Scheme. Supporting Information Available: CIF files, figures, and tables giving crystallographic data of 1 and 2 and the solid-state structure of 2 with selected bond lengths and angles. This material is available free of charge via the Internet at http:// pubs.acs.org. The CCDC files 725530 (for 1) and 725531 (for 2) also contain supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif.
