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Organometallics 2009, 28, 4258–4261 DOI: 10.1021/om9002889
Synthesis of [{2,6-(Me2NCH2)2C6H3}Sn(OH)O]6: an NfSn Coordinated Stannonic Acid
Marek Bouska,† Libor Dost al,† Robert Jirasko,‡ Ales Ruzicka,† and Roman Jambor*,† †
Department of General and Inorganic Chemistry and ‡Department of Analytical Chemistry, Faculty of legiı´ 565, CZ-532 10, Pardubice, Czech Republic Chemical Technology, University of Pardubice, Cs. Received April 16, 2009
Summary: The discovery of the possible hydrolytic mechanism of the monoorganotin(IV) compound RSn(H2O)(O2CCF3)3 (2) resulted in the preparation of the first intramolecularly coordinated stannonic acid, [RSn(OH)O]6 (3) (R is the N, C,N-pincer ligand [2,6-(Me2NCH2)2C6H3]-). The presence of NfSn coordination prevents the formation of additional Sn-O interactions and results in the stabilization of the unique centrosymmetric {Sn6O12} core in 3. The hydrolysis of monoorganotin compounds is an interesting topic of current organotin chemistry. The previous knowledge concerning this topic can be summarized by the statement that the hydrolytic products are only ill-defined products called organostannonic acids of the formula [RSn(OH)O]n. Methylstannonic acid, [MeSn(OH)O]n,1 first reported in 1922, and butylstannonic acid, [BuSn(OH)O]n, are amorphous solids that have a polymeric structure and contain four-, five-, and six-coordinated tin atoms, on the basis of 119Sn MAS NMR studies.2 These acids are, however, of industrial importance, as they are used in organic synthesis3 and in catalytic reactions.4 Current knowledge of the hydrolytic reactions suggested that clusters of low molecular weight and variable sizes can be stabilized, depending on the nature of the organic group bonded to the tin atom.5 A discrete product of a formal hydrolysis of monoorganotin trihalide was isolated for the first time in 1999, when the reaction of TsiSnBr3 (Tsi = tris(trimethylsilyl)methyl) with Na2O in liquid ammonia gave a product with the *To whom correspondence should be addressed. E-mail: roman.
[email protected]. (1) Lambourne, H. J. Chem. Soc. 1922, 121, 2533. (2) (a) Luitjen, J. G. A. Recl. Trav. Chim. Pays-Bas 1966, 85, 873. (b) Davies, A. G.; Smith, L.; Smith, P. J. J. Organomet. Chem. 1972, 39, 279. (c) Ribot, F.; Eychenne-Baron, C.; Fayon, F.; Massiot, D.; Bresson, B. Main Group Met. Chem. 2002, 25, 115. (d) Eychenne-Baron, C.; Ribot, F.; Steunou, N.; Sanchez, C.; Fayon, F.; Biesemans, M.; Martins, J. C.; Willem, R. Organometallics 2000, 19, 1940. (3) (a) Shibata, I.; Yoshida, T.; Kawakami, T.; Baba, A.; Matsuda, H. J. Org. Chem. 1992, 57, 4049. (b) Nozaki, K.; Oshima, K.; Utimoto Tetrahedron 1989, 45, 923. (c) Hanessian, S.; Leger, R. J. Am. Chem. Soc. 1992, 114, 3115. (d) Nakamura, E.; Tanaka, K.; Aoki, S. J. Am. Chem. Soc. 1992, 114, 9715. (e) Plamondon, L.; Wuest, J. D. J. Org. Chem. 1991, 56, 2066. (f) Sato, T.; Wakahara, Y.; Otera, J.; Nozaki, H. Tetrahedron 1991, 47, 9773. (4) (a) Furlan, R. L. E.; Mata, E. G.; Mascaretti, O. A. Tetrahedron Lett. 1998, 39, 2257. (b) Mascaretti, O. A.; Furlan, R. L. E.; Salomon, C. J.; Mata, E. G. Phosphorus, Sulfur Silicon Relat. Elem. 1999, 150, 89. (c) Davies, A. G. Organotin Chemistry, 2nd ed., Wiley-VCH: Weinheim, Germany, 2004.(d) Jousseaume, B.; Laporte, C.; Rascle, M.-C.; Toupance, T. Chem. Commun. 2003, 1428. (e) Camacho, C.; Biesemans, M.; Van Poeck, M.; Mercier, F. A. G.; Willem, R.; Darriet-Jambert, K.; Jousseaume, B.; Toupance, T.; Schneider, U.; Gerigk, U. Chem. Eur. J. 2005, 11, 2455. (5) (a) Janssen, J.; Magull, J.; Roesky, H. W. Angew. Chem., Int. Ed. 2002, 41, 1365. (b) Wraage, K.; Pape, T.; Herbst-Irmer, R.; Noltemeyer, M.; Schmidt, H.-G.; Roesky, H. W. Eur. J. Inorg. Chem. 1999, 869. pubs.acs.org/Organometallics
Published on Web 07/09/2009
composition [(TsiSn)4O6], an adamantane-type Sn4 cluster.5b The hydrolysis of TsiSnCl3 yielded the trimeric chloro compound [{TsiSn(O)Cl}3], in contrast to the expected stannonic acid [{TsiSn(OH)O}3]. This compound was, however, prepared by treatment of [{TsiSn(O)Cl}3] with LiOH and represents the first example of a structurally characterized stannonic acid.5a Later studies dealing with the hydrolysis of 2,4,6-iPr3C6H2Sn(CCMe)3 yielded [(2,4,6-iPr3C6H2Sn)8(μ4-O)2(μ3-O)8(μ2-O)4(μ2-OH)8{Sn(OH)}4] and [(2,4,6-iPr3C6H2Sn)6(OH)4(μ3-O)4(μ2-O)2(μ2-OH)2], respectively, the Sn12 and Sn6 oxide-hydroxide clusters containing the stannonic acid 2,4,6-iPr3C6H2Sn(OH)O moiety having both terminal and bridging OH groups.6 The reactions of n-butylstannonic acid with carboxylic or phosphorus-based acids lead to the formation of different monoorganooxotin (IV) cages or clusters as well.7 These studies showed that the successful synthesis of stannonic acid is related to the employment of rather bulky substituents such as a variety of substituted aryl and silyl groups, giving rise to kinetic stabilization. Very recently, we have shown that not only the use of bulky substituents but also an intramolecular NfSn interaction can be an alternative for the stabilization of reactive species such as diorganodistannynes RSnSnR, where R is the so-called N,C,Npincer ligand 2,6-(Me2NCH2)2C6H3.8 In our continuing studies on NfSn coordinated organotin(IV) compounds, we have focused our attention on the hydrolysis of organotin compounds bearing this ligand R. Herein, we describe the preparation of the NfSn coordinated hexameric monoorganotin acid [RSn(OH)O]6. The treatment of RSnI2Cl (1) with 3 equiv of AgO2CCF3 in wet CH2Cl2 yielded the air-stable compound RSn(H2O)(O2CCF3)3 (2).
(6) Prabusankar, G.; Jousseaume, B.; Toupance, T.; Allouchi, H. Angew. Chem., Int. Ed. 2006, 45, 1255. (7) (a) Chandrasekhar, V.; Nagendran, S.; Bansal, S.; Kozee, M. A.; Powell, D. R. Angew. Chem., Int. Ed. 2000, 39, 1833. (b) Chandrasekhar, V.; Gopal, K.; Thilagar, P. Acc. Chem. Res. 2007, 40, 420. (c) Chandrasekhar, V.; Boomishankar, R.; Gopal, K.; Sasikumar, P.; Singh, P.; Steiner, A.; Zacchini, S. Eur. J. Inorg. Chem. 2006, 4129. (d) Chandrasekhar, V.; Gopal, K Appl. Organomet. Chem. 2005, 19, 429. (8) Jambor, R.; Kasna, B.; Kirscher, K. N.; Sch€ urmann, M.; Jurkschat, K. Angew. Chem., Int. Ed. 2008, 47, 1650. r 2009 American Chemical Society
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Figure 1. Molecular structure of 2 (ORTEP drawing, thermal ellipsoid plot (50% probability)). Scheme 1. Possible Formation of RSn(OH)O by the Hydrolysis of 2 in ESI-MS Trap
The 119Sn NMR spectrum of 2 showed a signal at -515 ppm, defining the presence of a hexacoordinated tin atom.9 The 1H NMR spectrum of 2 showed the presence of two signals at 3.81 and 4.61 ppm for CH2N and at 2.64 and 2.82 ppm for Me groups and a signal at 10.7 ppm indicating the presence of a NHþ proton. This pointed to the fact that one proton of the H2O molecule coordinates to the CH2NMe2 group, resulting in the formation of the [CH2NHMe2]þ moiety. This coordination shows both the strong acidic character of the coordinated H2O molecule in 2 and prevents the fluxional exchange process of both CH2NMe2 groups,10 leading to the nonequivalent CH2NMe2 groups in 2 as the result. The X-ray structure analysis of 2 proved the presence of two nonequivalent CH2NMe2 groups and showed that both (9) (a) Holecek, J.; Nadvornı´ k, M.; Handlı´ r, K.; Lycka, A. J. Organomet. Chem. 1983, 241, 177. (b) Beckmann, J.; Dakternieks, D.; Duthie, A.; Mitchell, C. Dalton Trans. 2003, 3258. (10) (a) Handwerker, H.; Leis, C.; Probst, R.; Bassinger, P.; Grohmann, A.; Kiprof, P.; Herdtweek, F.; Bl€ umel, J.; Auner, N.; Zybill, C. Organometallics 1993, 12, 2162. (b) Kana, B.; Jambor, R.; Dostal, L.; Kolaova, L.; Císaova, I.; Holecek, J. Organometallics 2006, 25, 148. (11) Crystal data for 2 are as follows: monoclinic, space group P21/c, a=15.1081(10) A˚, b=9.0712(9) A˚, c=18.4858(17) A˚, β=108.624(6)°, V= 2400.7(4) A˚3, F=1.846 g cm-3, Z=4. Final R indices (I > 2σ(I)): R1= 0.036, wR2 = 0.083. The crystals were grown by slow diffusion of CH2Cl2. The structure was solved by direct methods (SIR92)13 and refined by a full-matrix least-squares procedure based on F2 (SHELXL97).14
hydrogen atoms of the coordinated water molecule (O1) are involved in the hydrogen-bonding interactions,11 one with the nitrogen atom of CH2NMe2 group (N2-O1=2.954(4) A˚), and the second one forms an O-H- - -O hydrogen bond ˚ with one of the CF3CO2 groups (O5-O1=2.848(4) A) (see Figure 1). The identity of 2 was also confirmed by electrospray ionization (ESI) mass spectrometry. The ESI-MS spectrum of 2 showed the presence of hydrolyzed product ions at m/z 689 [(RSn(OH)O)2 þ H]þ and m/z 671 [(RSn(OH)O)2 þ H H2O]þ and indicated the possible formation of the stannonic acid RSn(OH)O by the hydrolysis of 2. The easy elimination of HO2CCF3 acid from 2 may result from the presence of a O(w)-H- - -O(O2CCF3) hydrogen bond, forming the new Sn-OH bond (Scheme 1). Armed with this knowledge, we treated compound 2 with 3 equiv of KOtBu as a neutralizing agent to remove HO2CCF3 acid. This reaction resulted in the isolation of [RSn(OH)O]6 (3).
The NMR data for 3 showed only one set of resonances for the relevant nuclei (1H, 13C, 119Sn). The chemical shift of δ(119Sn) -475 ppm indicated the presence of a hexacoordinated9 tin atom in 3 and is shifted upfield compared with that for
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Bou ska et al. Scheme 2. Comparison of Strip Schematic Representations of 3 (Left) and [(2,4,6-iPr3C6H2Sn)6(OH)4(μ3-O)4(μ2-O)2(μ2-OH)2] (Right)
Figure 2. Full scan positive ion ESI mass spectrum (A) and MS/ MS of m/z 1341 [R4Sn4O5H]þ (B) for 3.
Figure 4. Coordination of Kþ ion to the {Sn6O12} core in 3 3 KO2CCF3.
Figure 3. Molecular structure of 3 3 KO2CCF3 (ORTEP drawing, thermal ellipsoid plot (50%probability)). The hydrogen atoms (except OH) were omitted for clarity.
1341 corresponding to [R4Sn4O5H]þ. Moreover, the easy loss of the RSn(OH)O moiety was observed in its tandem mass spectrum (see Figure 2). Single crystals of 3 3 KO2CCF3 were obtained by slow diffusion from a CH2Cl2 solution and were characterized by X-ray crystallography.12 The molecular structure of 3 3 KO2CCF3 is shown in Figure 3. The structure of 3 3 KO2CCF3 is unique. The centrosymetric {Sn6O12} core of cluster 3 is composed of six {Sn2O2} distannoxane motifs defining a hexameric cycle, with the average diameter of the cycle being Sn 3 3 3 Sn=6.5486(6) A˚. All six hexacoordinated Sn atoms are equal and form a central plane of the cluster. Six oxygen atoms are above and six oxygen atoms are below this plane, having no additional OfSn contact behind the {Sn2O2} core. This is in contrast with the Sn6 oxide-hydroxide cluster [(2,4,6-iPr3C6H2Sn)6(OH)4(μ3-O)4(μ2-O)2(μ2-OH)2], where
the trimeric monoorganotin acid [{TsiSn(OH)O}3], where tetrahedral coordination of the tin atom was defined (δ(119Sn) -156 ppm).5a The presence of penta- and hexacoordinated tin centers is thus more typical of the Sn6 oxide-hydroxide cluster [(2,4,6-iPr3C6H2Sn)6(OH)4(μ3O)4(μ2-O)2(μ2-OH)2], where the range of δ(119Sn) is from -309 to -538 ppm.6 The 1H NMR spectrum revealed the nonequivalence of CH2NMe2 groups (the presence of two AX spin systems for methylene protons) and one type of Sn-OH hydrogen atom, which resonate as a singlet at δ 11.85 ppm. This observation indicates the presence of one chemically equivalent hydroxy group in the molecule. The positive ion full scan mass spectra of 3 showed an ion at m/z
(12) Crystal data for 3 3 KO2CCF3 are as follows: monoclinic, space group C2/c, a=26.8747(5) A˚, b=16.0436(6) A˚, c=25.7439(4) A˚, β= 115.888(12)°, V=9986.4(1) A˚3, F=1.577 g cm-3, Z=4. Final R indices (I > 2σ(I)): R1=0.044, wR2=0.108. The structure was solved by direct methods (SIR92)13 and refined by a full-matrix least-squares procedure based on F2 (SHELXL97).14 There are disordered solvents (THF, CH2Cl2) and a CF3CO2 anion in this structure. Attempts were made to model this disorder or split it into two or more positions, but these were unsuccessful. PLATON/SQUEEZE15 was used to correct the data for the presence of disordered solvent. (13) Altomare, A.; Cascarone, G.; Giacovazzo, C.; Guagliardi, A.; Burla, M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 1045. (14) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement; University of G€ottingen, G€ottingen, Germany, 1997. (15) Spek, A. L. Acta Crystalllogr., Sect. A 1990, 46, C34.
Communication
the six puckered four-membered {Sn2O2} rings form a cagelike arrangement, which can be described as a double-twist M€ obius band of stannoxane units (see Scheme 2, where a comparison of strip schematic representations of [(2, 4,6-iPr3C6H2Sn)6(OH)4(μ3-O)4(μ2-O)2(μ2-OH)2] and 3 is given).6 Another monoorganotin acid, [{TsiSn(OH)O}3], is the cyclic trimer Sn3O3 with three terminal OH bonds.5a All of the N,C,N-ligands R situated on the tin atoms are pointing outside the cage core, and the presence of the R ligand is crucial for the stabilization of this structural type. One nitrogen atom is involved in NfSn coordination (range of 2.378-2.432 A˚), while the second one is involved in O-H- - -N hydrogen bonding with the H atom of the SnOH group (O- - -N = 2.713-2.750 A˚, O-H- - -N = 129131°). The former nitrogen atom is thus responsible for the formation of the coordinatively saturated tin atom, and no additional Sn-O contacts are formed throughout the whole molecule of 3, enabling the formation of a centrosymmetric {Sn6O12} core. As the result of the absence of any additional Sn-O contacts, three oxygen atoms (those with shorter Sn-O bonds within the Sn2O2 core) above (O2a, O4a, and O6a) and below (O2, O4, and O6) the Sn6 plane coordinate to the potassium cation. The overall geometry of 3 3 KO2CCF3 can be described as a Kþ-capped {Sn6O12} cluster (see Figure 4) with half-occupancy of the potassium electrons below and the other half above the plane made up of tin atoms.
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In summary, the discovery of the possible hydrolytic mechanism of 2 resulted in the isolation of the first intramolecularly coordinated stannonic acid, 3. The presence of NfSn coordination prevents the formation of additional Sn-O interactions, which are usually found in Sn clusters, and results in the stabilization of the unique centrosymmetric {Sn6O12} core. The absence of Sn-O interactions within the cluster resulted in the coordination of the potassium cation by oxygens and in the stabilization of 3 3 KO2CCF3. The investigation of the possible coordination of other cations is of current interest.
Acknowledgment. We thank the Czech Science Foundation of the Czech Republic (Project No. GA370468) and the Ministry of Education of the Czech Republic (Project Nos. VZ0021627501, VZ0021627502, and LC523). Supporting Information Available: Text and figures giving experimental details for the preparation and full characterization of 1-3 and for the preparation and characterization of RSn (H2O)(OAc)3 and for its reactivity with KOtBu and CIF files giving crystallographic data for compounds 2 and 3. This material is available free of charge via the Internet at http:// pubs.acs.org. These crystallographic data have also been deposited with the Cambridge Crystallographic Data Centre (CCDC Nos. 723591 and 723592).
