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Organometallics 2009, 28, 42–44
First Example of a Hydrated Monoorganotin Cation: Synthesis and Structure of [{PhSn(H2O)3(µ-OH)}2][{1,5-C10H6-(SO3)2}2] Vadapalli Chandrasekhar* and Puja Singh Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, India ReceiVed October 9, 2008 Summary: The reaction of Ph2SnO with naphthalene-1,5-disulfonic acid tetrahydrate affords, through a Sn-aryl bond cleaVage process, the first example of a hydrated monoorganotin cation, [{PhSn(H2O)3(µ-OH)}2][{1,5-C10H6-(SO3)2}2]. The structural elucidation of the latter showed that it contained a tetracationic dinuclear unit where the two tin atoms are bridged by two hydroxide ligands and each tin is hydrated with three molecules of water. Intermolecular hydrogen-bonding interactions between the water molecules and the disulfonate anions result in a pillared three-dimensional network. Organotin oxides, hydroxides, and oxide hydroxides are versatile starting materials for the preparation of a number of organostannoxane assemblies.1 Despite their widespread use in organotin chemistry, there have not been many efforts to understand the mechanism of formation of these organotin oxides/hydroxides/oxide hydroxides,2 although it is generally agreed that one possible means of their generation involves hydrolysis of hydrated organotin cations. Our approach to understand this problem has been to discover synthetic routes to assemble hydrated organotin cations and to hydrolyze them in a controlled manner. In the reactions of organotin oxides with arylsulfonic acids we were able to isolate the hydrated diorganotin cations [nBu2Sn(H2O)4]2+[2,5-Me2-C6H5-SO3]-2 (1a)3a and [{nBu2Sn(H2O)3(L)Sn(H2O)3nBu2}]2+[L]2- · 2MeOH · 2H2O (1b; L ) 1,5-C10H6-(SO3)2).3b We were able to show that a direct hydrolysis of the former with pyridine leads to the 2D stannoxane polymer [{nBu2Sn(µ-OH)(O3-SC6H3-2,5-Me2)}2]n.4a On the other hand, by a variation of reaction conditions we recently isolated the dinuclear compound [(Phen)(NO3)Me2Sn(µOH)SnMe2(NO3)(Phen)][NO3], where the two tin centers are bridged by a single hydroxide ligand.4b All of these pertain to diorganotin compounds, and there has not been a single example of a hydrated monoorganotin cationic compound thus far. The main difficulty for this gap lies in finding appropriate synthetic procedures. The reaction of nBuSn(O)(OH) with various sulfonic acids has been investigated previously. In all the cases the main * To whom correspondence should be addressed. E-mail:
[email protected]. Tel: (+91) 512-259-7259. Fax: (+91) 521-259-0007/7436. (1) (a) Davies, A. G. Organotin Chemistry, Wiley-VCH: Weinheim, Germany, 2004. (b) Chandrasekhar, V.; Gopal, K.; Thilagar, P. Acc. Chem. Res. 2007, 46, 420. (c) Chandrasekhar, V.; Nagendran, S.; Baskar, V. Coord. Chem. ReV. 2002, 235, 1. (d) Beckmann, J.; Jurkschat, K. Coord. Chem. ReV. 2001, 215, 267. (e) Jain, V. K. Coord. Chem. ReV. 1994, 135/136, 809. (f) Holmes, R. R. Acc. Chem. Res. 1989, 22, 190. (2) (a) Beckmann, J.; Henn, M.; Jurkschat, K.; Schu¨rmann, M. Organometallics 2002, 21, 192, and references therein. (b) Heinrich, P.; Hans, R. J. Organomet. Chem. 1989, 364, 57. (c) Heinrich, P.; Hans, R. J. Organomet. Chem. 1989, 368, 173. (d) Heinrich, P.; Hans, R. J. Organomet. Chem. 1989, 373, 173. (3) (a) Chandrasekhar, V.; Boomishankar, R.; Singh, S.; Steiner, A.; Zacchini, S. Organometallics 2002, 21, 4575. (b) Chandrasekhar, V.; Boomishankar, R.; Steiner, A.; Bickley, J. F. Organometallics 2003, 22, 3342. (4) (a) Chandrasekhar, V.; Singh, P.; Gopal, K. Organometallics 2007, 26, 2833. (b) Chandrasekhar, V.; Singh, P. Organometallics 2008, 27, 4083.
product isolated is the dodecanuclear football-shaped cage [(RSn)12O14(OH)6]2+[R′SO3]-2.5 We have tried to approach the synthesis of hydrated monoorganotin cations in a different way. Recently there has been interest in the use of Sn-C bond cleavage reactions among aryl- and alkyltin compounds as viable synthetic procedures for preparing organooxotin compounds.6 Although most of these reactions occur with carboxylic/ phosphonic/phosphinic acids, recent reports from our laboratory3b and that of Beckmann7 suggested that Sn-C bond cleavage reactions can also occur in the reactions of organotin precursors with sulfonic acids. Spurred by this, we investigated the reaction of Ph2SnO with naphthalene-1,5-disulfonic acid tetrahydrate. In this reaction we were able to isolate, by a Sn-aryl bond cleavage process, the first example of a hydrated monoorganotin cation, [PhSn(H2O)3(µ-OH)]2[1,5-C10H6-(SO3)2]2 (2). The structural elucidation of the latter showed that it contained a tetracationic dinuclear core where the two tin atoms are bridged by two hydroxide ligands and each tin is coordinated with three molecules of water (Figure 1). Compound 2 represents an unprecedented example of a hydrated monorganotin cation that is formed presumably by the hydrolysis of the putative [PhSn(H2O)5]3+ species. In comparison to the case for monoorganotin cations, cationic diorganotin compounds are more well-known.8 In comparison to Sn-alkyl bonds, Sn-aryl bonds are more prone to cleavage during reactions with protic acids. In view of this, we have investigated the reaction of Ph2SnO with naphthalene-1,5-disulfonic acid with a view to isolate Sn-Ph cleaved products. Accordingly, the reaction of Ph2SnO with naphthalene-1,5-disulfonic acid tetrahydrate (LH2), in a mixture of toluene and methanol (5:3) at room temperature for 4 days, afforded colorless crystals (32% yield)9 which were identified as [PhSn(H2O)3(µ-OH)]2[1,5-C10H6-(SO3-)2]2, (2) (Scheme 1). The latter crystallized as its water solvate, 2 · 3H2O. The 119Sn (5) (a) Chandrasekhar, V.; Boomishankar, R.; Gopal, K.; Sasikumar, P.; Singh, P.; Steiner, A.; Zacchini, S. Eur. J. Inorg. Chem. 2006, 4129. (b) Eyechenne-Baron, C.; Ribot, F.; Sanchez, C. J. Organomet. Chem. 1998, 567, 137. (c) Eyechenne-Baron, C.; Ribot, F.; Steunou, N.; Sachez, C.; Fayon, F.; Biesemans, M.; Martins, J. C.; Willem, R. Organometallics 2000, 19, 1940. (6) (a) Chandrasekhar, V.; Gopal, K.; Sasikumar, P.; Thirumoorthi, R. Coord. Chem. ReV. 2005, 249, 1745. (b) Chandrasekhar, V.; Sasikumar, P.; Thilagar, P. Organometallics 2007, 26, 4386. (c) Xie, Y. P.; Yang, J.; Ma, J. F.; Zhang, L. P.; Song, S. Y.; Su, Z. M. Chem. Eur. J. 2008, 14, 4093. (d) Zheng, G. L.; Ma, J. F.; Su, Z. M.; Yan, L. K.; Yang, J.; Li, Y. Y.; Liu, J. F. Angew. Chem. 2004, 116, 2463; Angew. Chem., Int. Ed. 2004, 43, 2409. (e) Song, S. Y.; Ma, J. F.; Yang, J.; Gao, L. L.; Su, Z. M. Organometallics 2007, 26, 2125. (f) Ma, C.; Sun, J.; Zhang, R. J. Mol. Struct. 2007, 833, 203. (g) Zhang, R.; Zhang, Q.; Shi, Y.; Ma, C. J. Organomet. Chem. 2006, 691, 1668. (h) Prabusankar, G.; Jousseaume, B.; Toupance, T.; Allouchi, H. Angew. Chem., Int. Ed. 2006, 45, 1255, and references therein. (7) Beckmann, J.; Dakternieks, D.; Duthie, A.; Mitchell, C. Appl. Organomet. Chem 2004, 18, 54. (8) Kasˇna´, B.; Dosta´l, L.; Cı´sarˇova´, I.; Roman, J. Organometallics 2007, 26, 4080, and references therein.
10.1021/om800972m CCC: $40.75 2009 American Chemical Society Publication on Web 12/05/2008
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Organometallics, Vol. 28, No. 1, 2009 43 Scheme 1. Synthesis of 2
NMR spectrum of 2 · 3H2O in (CD3)2SO solution displayed a single peak at -577 ppm, consistent with the presence of a hexacoordinated tin (1C,5O) in solution.10 The ESI-MS spectrum of 2 · 3H2O revealed a highest observable peak at m/z 1136.70 corresponding to the dimeric species [{PhSn(H2O)3(µ-OCH3)Sn(H2O)3Ph} + 2 L} + H+]+, indicating that the dinuclear structure found in the solid state is retained in solution, although the bridging hydroxide ligand is replaced with methoxide. The fragmentation pattern reveals the presence of other fragments, also including mononuclear species (see Figure S3 in the Supporting Information). ESI-MS analysis also indicates that the reaction of Ph2SnO with 1,5-naphthalenedisulfonic acid proceeds through a disproportionation pathway. Accordingly, the ESI-MS spectrum of the crude sample obtained in this reaction, prior to recrystallization, showed peaks corresponding to triorganotin cationic species in addition to those identified for monoorganotin species (see Figure S4 in the Supporting Information). Thermogravimetric analysis of 2 · 3H2O reveals a sequential loss of water molecules followed by loss of the naphthalenedisulfonate. The final char yield at around 550 °C is quite substantial and is about 36.8% (see Figure S5 in the Supporting Information). The compound 2 · 3H2O contains the tetracationic dinuclear tin complex [{PhSn(µ-OH)(H2O)3}2]4+. The four positive charges present on the complex are compensated by the presence of two naphthalene-1,5-disulfonate anions (Figure 1, Scheme 1). The dimeric core of the tetracation of 2 · 3H2O, shown in Figure 1, consists of two centrosymmetrically related tin centers. Each tin is hexacoordinate in a distorted-octahedral geometry. The coordination environment around each tin consists of one phenyl substituent and three molecules of water. Two such tin centers are bridged to each other by two hydroxide ligands, leading to the formation of a central [Sn2(µ-OH)2] unit. Unlike the case for diorganotin compounds, the occurrence of discrete dimeric [Sn2(µ-OH)2] motifs is not very common among monoorganotin compounds. Previous instances of dimeric monoorganotin units include compounds containing [Sn2(µ-OH)2] [RSn(OH)Cl2(H2O)] (R ) Et, nBu, iBu, iPr, Me), [{2,6(P(O)(OEt)2)2-4-tBu-C6H2}SnF2OH]2, etc. and have been reviewed recently.10 Selected bond distance/angle data for 2 · 3H2O are given below Figure 1. The trans angles around each tin are as follows: O1-Sn1-C1 ) 171.49(10)°, O2-Sn1-O1* ) 159.97(8)°, and
O3-Sn1-O4 ) 167.45(10)°. The Sn-O distances involving the central four-membered [Sn2(µ-OH)2] motif are as follows: Sn1-O1 ) 2.044(2) Å and Sn1-O1* ) 2.106(2) Å. These distances are shorter in comparison to those found among similar structural units of diorganotin compounds: [nBu2SnOH(OTf)(H2O)]2 (2.116(3) Å), [tBu2SnOH(OTf)(H2O)]2 (2.113(4) Å), and [(S)-2PB2SnOH(OTf)(H2O)]2 (2.114(7) Å) ((S)-2PB ) (S)-2-phenylbutyl).11 Interestingly, in 2 the coordinated water molecules (O2, O3, and O4) are bound more firmly to the tin center (Sn1-O2 ) 2.087(2) Å, Sn1-O3 ) 2.130(2) Å, Sn1-O4 ) 2.109(2) Å; see caption of Figure 1) in comparison to those in [nBu2Sn(H2O)4]2+[2,5-Me2-C6H5-SO3]-2 (2.271(3)Å)3aor[{nBu2Sn(H2O)3(1,5-C10H6-(SO3)2)Sn(H2O)3nBu2}]2+[1,5C10H6-(SO3)2)]2- · 2MeOH · 2H2O (2.20(6) Å).3b The shorter Sn-O distances found in 2 · 3H2O may be due to the increased Lewis acidic character of the tin centers owing to the tetracationic nature of the complex as well as the presence of a phenyl substituent on each tin. The crystal structure of 2 · 3H2O reveals the presence of extensive and strong intermolecular hydrogen-bonding interactions (see Table S1 in the Supporting Information). The asymmetric unit of 2 · 3H2O contains three coordinated and three noncoordinated water molecules. Hydrogen-bonding interactions between all of these water molecules and the disulfonate anions glues four dimeric units together (Figure 2a). These interactions extend the supramolecular structure along the crystallographic ab plane to form a two-dimensional sheet (Figure 2a; for an extended view see Figure S2a in the Supporting Information). This sheet is single-layered, in contrast to the triple-layered 2D sheets found in 1b.3b All the four-membered [Sn2(µ-OH)2] units are present in a parallel arrangement along the crystallographic b axis (Figure S2b). Adjacent 2D sheets of 2 · 3H2O are connected to each other through naphthyl groups of the anion. These naphthyl pillars are responsible for taking the structure into a final three-dimensional assembly (Figure 2b). The interlayer distance in this assembly is 8.90 Å and may be compared with that found in 1b (11.5 Å). The free space present in the 3D assembly is occupied by the phenyl substituents present on tin atoms and is therefore unavailable for other guest molecules. In conclusion, we have been able to isolate the first example of a hydrated monorganotin cation through an Sn-aryl bond cleavage involving the reaction of Ph2SnO with naphthalene-1,5-disulfonic acid. In view of the possibility
(9) Synthesis of 2 · 3H2O: Ph2SnO (0.11 g, 0.37 mmol) and naphthalene1,5-disulfonic acid tetrahydrate (0.14 g, 0.37 mmol) were taken up in a mixture of toluene and methanol (5:3), and this mixture was stirred for 4 days at room temperature. The mixture was filtered, and the filtrate was allowed to evaporate at room temperature. Blocklike crystals of 2 · 3H2O were obtained after a few weeks. Yield: 0.07 g (32%, for isolated crystals). Mp: 250 °C dec. Anal. Calcd for C16H24O13S2Sn (607.97 g): C, 31.58, H, 3.98. Found: C, 31.62, H, 4.03. IR (KBr, cm-1): 3434 (br, ν(H2)), 1205 (s, ν(SO3) asym str), 1043 (s, ν(SO3) sym str), 996 (s, ν(SO3) ionic), 609 (m, ν(C-S)). 1H NMR (500 MHz, (CD3)2SO): δ 7.33-7.40 (m, 5H, phenyl CH), 8.83 (d, 2H, naphthyl CH), 7.90 (d, 2H, naphthyl CH), 7.49-7.51 (m, 2H, naphthyl CH). 119Sn NMR (500 MHz, (CD3)2SO): δ-577 (s). (10) Chandrasekhar, V.; Singh, P.; Gopal, K. Appl. Organomet. Chem. 2007, 21, 483.
(11) Sakamoto, K.; Ikeda, H.; Akashi, H.; Fukuyama, T.; Orita, A.; Otera, J. Organometallics 2000, 19, 3242. (12) Crystal data for 2: size 0.2 × 0.2 × 0.1 mm3; triclinic; space group P1j; a ) 10.495(5) Å, b ) 10.796(5) Å, c ) 11.583(5) Å; R ) 72.431(5)°, β ) 76.672(5)°, γ ) 61.853(5)°; V ) 1097.1(9) Å3; T ) 153(2) K; Z ) 2; Dcalcd ) 1.838 Mg m-3; θ range 2.20-25.00°; 5681 reflections collected; 3798 independent reflections (Rint ) 0.0149); R1 ) 0.0241, wR2 ) 0.0623 (for I > 2σ(I)); R1 ) 0.0252, wR2 ) 0.0636 (for all data); GOF ) 1.071. The structure was solved and refined by full-matrix least squares on F2 using the SHELXTL software package.13 All the hydrogens of the water molecules and the hydrogen of the hydroxyl group were located from the difference map and refined. (13) Sheldrick, G. M. SHELXTL version 6.14; Bruker AXS Inc., Madison, WI, 2003.
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Organometallics, Vol. 28, No. 1, 2009
Figure 1. ORTEP representation of asymmetric unit of 2 · 3H2O showing 50% probability displacement ellipsoids. Hydrogen atoms have been omitted for clarity. Selected bond distances (Å) and bond angles (deg) are as follows: Sn1-O1 ) 2.044(2), Sn1-O2 ) 2.087(2), Sn1-O3 ) 2.130(2), Sn1-O4 ) 2.109(2), Sn1-C1 ) 2.103(3), O1-H101 ) 0.689(5); O1-Sn1-C1 ) 171.49(10), O1-Sn1-O2 ) 87.87(9), O1-Sn1-O1* ) 72.45(10), O1-Sn1-O4 ) 83.40(10), O1-Sn1-O3 ) 88.02(9), O2-Sn1-C1 ) 99.73(10), O2-Sn1-O1*)159.97(8),O2-Sn1-O4)86.73(10),O2-Sn1-O3 ) 83.80(10), O3-Sn1-O4 ) 167.45(10), O1*-Sn1-O4 ) 94.49(9), O1*-Sn1-O3 ) 91.62(9), C1-Sn1-O3 ) 96.56(11), C1-Sn1-O4)93.14(11),C1-Sn1-O1*)100.16(10),Sn1-O1-Sn1* ) 107.55(10). See Figure S1 in the Supporting Information for a complete atom-labeling scheme.
that pentaaquo cations such as [ArSn(H2O)5]3+ are involved in the formation of [PhSn(H2O)3(µ-OH)]2[C10H6-1,5-(SO3)2]2, it would be interesting to find out synthetic routes for the preparation of stable members of this family. In addition to being interesting examples possessing rich hydrogen bonding, compounds such as [ArSn(H2O)5]3+[X]3- would also be valuable precursors for the preparation of novel organostannoxanes by controlled hydrolysis reactions. We are currently exploring these possibilities.
Acknowledgment. We are thankful to the Department of Science and Technology (DST), New Delhi, for financial support, including support for the CCD X-ray diffractometer
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Figure 2. (a) View of a section of the 2D sheet of 2 · 3H2O along the ab plane. Four dimeric units are glued together through intermolecular H-bonding interactions. Phenyl groups have been omitted for clarity. For metric parameters see Table S1 in the Supporting Information. (b) View of the three-dimensional pillared structure of 2 · 3H2O along the b axis. Adjacent sheets (shown in the space-filling model) are linked together by “naphthyl” groups of naphthalene-1,5-disulfonate anions.
facility at IIT-Kanpur. P.S. thanks the Council of Scientific and Industrial Research of India for a Senior Research Fellowship. V.C. is grateful to the DST for a J. C. Bose National fellowship. V.C. is a Lalit Kapoor chair professor. Supporting Information Available: A CIF file giving crystallographic data for 2 · 3H2O and figures, tables, and text giving additional views of 2 · 3H2O, ESI-MS spectra of 2 · 3H2O, ESI-MS spectra of crude product 2a, a thermogravimetric curve for 2 · 3H2O, and additional experimental details. This material is available free of charge via the Internet at http://pubs.acs.org. OM800972M
