Novel Zwitterionic Sulfides, Selenides and Tellurides [1]

Transcription

1 Novel Zwitterionic Sulfides, Selenides and Tellurides [1] Norbert Kuhn,* Ahmed Al-Sheikh, Manfred Steimann, and Markus Ströbele Tübingen, Institut für Anorganische Chemie der Universität Received April, 8th, Dedicated to Professor Wolfgang Malisch on the Occasion of his 60th Birthday Abstract. The zwitterionic compounds Im-E-Mel [9, E S(a), Se (b), Te (c), Im 2-{1,3-diisopropyl-4,5-dimethylimidazolium}, Mel 5-{2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-ylide}] are obtained from the corresponding 2-chalcogeno-1,3-diisopropyl-4,5-dimethylimidazolines 8 and 5-bromo-2,2-dimethyl-4,6-dioxo-1,3-dioxan (7) in the presence of triethylamine in excellent yields. The crystal structures of the thermally stable compounds reveal most effective charge separations from which the compounds 9 resemble closely to diaryl chalkogenides. 9b and 9c are the first selenocarbonyl and tellurocarbonyl ylides reported, to our knowledge. Keywords: Heterocycles; Zwitterionic states; Sulfur; Selenium; Tellurium; Crystal structure Neuartige zwitterionische Sulfide, Selenide und Telluride [1] Inhaltsübersicht. Die zwitterionischen Verbindungen Im-E-Mel [9, E S (a), Se (b), Te (c), Im 2-{1,3-Diisopropyl-4,5- dimethylimidazolium}, Mel 5-{2,2-Dimethyl-4,6-dioxo-1,3-dioxan-5-ylid}] werden durch Umsetzung der entsprechenden 2- Chalkogeno-1,3-diisopropyl-4,5-dimethylimidazoline 8 mit 5- Brom-2,2-dimethyl-4,6-dioxo-1,3-dioxan (7) in Gegenwart von Triethylamin in sehr guten Ausbeuten erhalten. Die Kristallstrukturen der thermisch stabilen Verbindungen zeigen eine ausgeprägte Ladungstrennung woraus sich eine enge Verwandtschaft von 9 mit den entsprechenden Diarylchalkogeniden ergibt. 9b and 9c sind nach unserer Kenntnis die ersten Vertreter der Seleno- bzw. Tellurocarbonylylide. Introduction Starting with the pioneering work of Middleton, Oae and Hartke [2], thiocarbonyl ylides (1; E S) have been used both as isolable and intermediate precursors in organic synthesis [3]. Despite their relevance for the discussion of bonding in these 1,3-dipolar species, only one publication containing crystallographic data (2) is available [4] (preliminary data of 3 have also been mentioned [5]). It is of interest that reports on the corresponding selenium and tellurium species (1, E Se, Te) seem to be completely absent from the literature. Heterocycles play an important role for the stabilization of zwitterionic structures due to their marked tendency of π-electron delocalisation, most common examples being the imidazolium (4) and 4,6-dioxo-1,3-dioxanide (5) fragments. The construction of push-pull compounds through combination of positively and negatively charged heterocyclic fragments opened up an important chapter of organic chemistry. The separation of the rings by resonance inhibiting heteroelements allows the formation of stable beta- Scheme 1 * Prof. Dr. N. Kuhn Institut für Anorganische Chemie der Universität Tübingen Auf der Morgenstelle 18 D Tübingen Fax: ( ) norbert.kuhn@uni-tuebingen.de Scheme 2 ines [6]. Continuing our work on imidazolium compounds (see e.g. [7 16]) and Meldrum s acid derivatives [1,17,18] we report on the syntheses and structures of novel zwitterionic Z. Anorg. Allg. Chem. 2003, 629, DOI: /zaac WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1541

2 N. Kuhn, A. Al-Sheikh, M. Steimann, M. Ströbele sulfides, selenides and tellurides containing imidazolium and dioxanide fragments. Synthesis and Structural Characterization of the Zwitterionic Diorganochalkogenides 9 Scheme 3 Beginning with its discovery [19] and correct structural assignment [20], Meldrum s acid (6) has become a widely used reagent in organic synthesis [21]. Recently, we published a new entrance to Meldrum s acid derivatives consisting of nucleophilic attack at 5-bromo-2,2-dimethyl-4,6-dioxo-1,3- dioxin (7) [22] in the presence of bases [17,18]. Using this route, the ylides 9 [E S(a), Se (b), Te (c)] are obtained from 7 and the mesoionic ureas 8a-c [10 12] as stable colourless crystals in excellent yield. On comparison with corresponding imidazolium salts (see e.g. [23]) as well as with the Meldrum s acid anion [1], their NMR and IR data confirm the presence of partial charges in both fragments (see experimental section). In 77 Se and 125 Te NMR [δ (9b), (9c)], the resonances are shifted towards the high field end of the diarylselenide and diaryltelluride ranges [24] and obey the prediction of McFarlaine s straight line [25]. To get a better insight into their bonding, we have investigated the crystal structures of 9 (Tables 1 5, Figs. 1 3). While 9a and 9b form isotypic crystals in the space group Cmc2 1, the tellurium compound 9c crystallizes in the monoclinic space group P2 1 /c. Apparently, the different packing Table 1 Crystal data of the compounds C 11 H 20 N 2 -E-C 6 H 6 O 4 (9) 9a (E S) 9b (E Se) 9c (E Te) C 17 H 26 N 2 O 4 S C 17 H 26 N 2 O 4 Se C 17 H 26 N 2 O 4 Te Unit cell dimension: a/å (6) (8) 8.685(1) b/å (7) (2) (4) c/å 9.635(6) 9.756(2) (2) α/ β/ (3) γ/ Cell volume / Å (2) 1880(1) (7) Z density [calc.]/g/cm crystal system orthorhombic orthorhombic monoclinic Space group Cmc2(1) Cmc2(1) P2 1 /c measurement device Siemens P4 Stoe IPDS-1 wave length temperature/ C theta range/ reflections: collected observed [F 0 >4σ(F 0 )] refinement full matrix least-squares method on F 2 parameter solution and refinement ShelXTL V5.1 (NT) R 1 -Value [I>2σ(I)] wr2-value [I>2σ(I)] R 1 -Value [all data] wr2-value [all data] largest difference peak and hole/e Å , , , WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim zaac.wiley-vch.de Z. Anorg. Allg. Chem. 2003, 629,

3 Novel Zwitterionic Sulfides, Selenides and Tellurides Table 2 Atomiccoordinates(x10 4 ) and equivalent isotropic displacement parameters (Å 2 x10 3 )forc 11 H 20 N 2 -S-C 6 H 6 O 4 (9a). U(eq) is defined as one third of the trace of the orthogonalized U ij tensor. x y z U(eq) S(1) (1) 7596(1) 21(1) N(1) 4243(1) 11122(1) 6177(1) 22(1) O(1) 5816(1) 7336(1) 5006(1) 35(1) O(2) 6639(1) 8443(1) 6173(2) 39(1) C(1) (1) 6578(2) 20(1) C(2) 4526(1) 11990(1) 5517(1) 24(1) C(3) 3888(1) 12743(1) 4884(2) 36(1) C(4) 3275(1) 10770(1) 6416(1) 24(1) C(5) 2786(1) 11412(1) 7491(2) 30(1) C(6) 2746(1) 10688(1) 5050(2) 35(1) C(7) (1) 6410(2) 23(1) C(8) 5863(1) 8136(1) 5919(2) 27(1) C(9) (1) 5018(2) 30(1) C(10) (2) 3679(3) 52(1) C(11) (1) 6286(3) 33(1) Table 3 Atomiccoordinates(x10 4 ) and equivalent isotropic displacement parameters (Å 2 x10 3 ) for C 11 H 20 N 2 -Se-C 6 H 6 O 4 (9b). U(eq) is defined as one third of the trace of the orthogonalized U ij tensor. Table 4 Atomic coordinates (x10 4 ) and equivalent isotropic displacement parameters (Å 2 x10 3 ) for C 11 H 20 N 2 -Te-C 6 H 6 O 4 (9c). U(eq) is defined as one third of the trace of the orthogonalized U ij tensor. x y z U(eq) Te(1) 743(1) 6181(1) 10624(1) 28(1) N(1) 2245(3) 7425(1) 10150(3) 28(1) N(11) 3906(3) 6682(1) 10172(3) 29(1) O(1) 338(3) 5100(1) 7099(2) 35(1) O(11) 1948(3) 5993(1) 6433(2) 34(1) O(2) 1449(3) 4967(1) 9157(2) 42(1) O(21) 1818(3) 6747(1) 7828(2) 41(1) C(1) 2435(4) 6818(1) 10272(3) 25(1) C(2) 3640(4) 7681(1) 9996(3) 32(1) C(21) 4681(4) 7215(1) 10019(3) 33(1) C(3) 3909(6) 8342(2) 9849(6) 57(1) C(31) 6340(6) 7265(2) 9896(7) 58(1) C(4) 817(4) 7759(2) 10275(4) 37(1) C(41) 4612(4) 6054(1) 10321(4) 34(1) C(5) 91(6) 8141(2) 9075(5) 55(1) C(51) 5027(6) 5862(2) 9131(4) 47(1) C(6) 1377(8) 8099(3) 11577(5) 72(2) C(61) 6058(6) 5993(2) 11633(4) 53(1) C(7) 207(4) 5862(1) 8696(3) 26(1) C(8) 371(4) 5297(1) 8407(3) 30(1) C(81) 1353(4) 6232(1) 7715(3) 29(1) C(9) 1927(4) 5346(1) 6324(3) 33(1) C(10) 2175(6) 5216(2) 4889(4) 45(1) C(11) 3266(5) 5075(2) 6754(4) 38(1) x y z U(eq) Se(1) (1) 5876(1) 21(1) N(1) 5754(1) 1171(1) 4322(2) 20(1) O(1) 4188(1) 2680(1) 3130(2) 34(1) O(2) 3372(1) 1573(1) 4298(2) 38(1) C(1) (2) 4732(2) 18(1) C(2) 5472(1) 2035(1) 3651(2) 23(1) C(3) 6109(2) 2780(2) 3017(3) 35(1) C(4) 6715(1) 806(1) 4553(2) 22(1) C(5) 7199(1) 1429(2) 5643(2) 30(1) C(6) 7251(1) 739(2) 3209(2) 34(1) C(7) (2) 4587(3) 22(1) C(8) 4139(1) 1896(1) 4057(2) 26(1) C(9) (2) 3136(3) 29(1) C(10) (3) 1807(4) 50(1) C(11) (2) 4379(4) 33(1) is influenced by the tendency of tellurium to enhance its coordination number. In the sulfur and selenium derivatives, as well as in 10 [17], we obseve only short intramolecular distances between the exocyclic oxygen and chalcogen atoms [9a: S(1)-O(2) 3.082(2) Å, S(1)-O(2)-C(8) 62.4(1) ; 9b: Se(1)-O(2) Å, Se(1)-O(2)-C(8) 64.7(1) ]. The tellurium compound 9c adopts a dimeric structure by additional intermolecular tellurium to oxygen contacts [Te(1)-O(2) 3.225(8), Te(1)-O(2A) 3.28(1) Å, Te(1)-O(2)- Te(1A) 112.5(1), O(2)-Te(1)-O(2A) 67.5(1) ]. Despite these differences, there are only minor deviations in the structures of the Meldrum s fragments in 9a-c (for details see table 5). Comparing the structure of their dioxin rings with Meldrum s acid (6) [26] and its anion [1], we see the enolate nature of 9 to be confirmed. Consequently, their imidazolium part resembles closely to the structures of imidazolium salts [23,27]. Though both being formally of bond order one in the zwitterionic resonance structure, the E-C bond lengths in each compounds 9 differ markedly, especially in the case of the tellurium compound 9c, though being in the range of Table 5 Selected bond lengths /Å and angles / for C 11 H 20 N 2 -E- C 6 H 6 O 4 (9). 9a (E S) 9b (E Se) 9c (E Te) E C(1) 1.763(2) 1.911(2) 2.165(3) E C(7) 1.745(2) 1.876(3) 2.069(3) C(1) N(1) 1.354(1) 1.348(2) 1.347(4) C(1) N(11) 1.355(4) N(1) C(2) 1.384(2) 1.387(2) 1.401(4) N(11) C(21) 1.393(4) C(2) C(2a) 1.371(3) 1.365(4) C(2) C(21) 1.362(4) C(7) C(8) 1.428(2) 1.424(2) 1.419(4) C(7) C(81) 1.419(4) C(8) O(1) 1.386(2) 1.385(2) 1.393(4) C(81) O(11) 1.397(4) C(8) O(2) 1.229(4) C(81) O(21) 1.226(4) O(1) C(9) 1.429(2) 1.425(2) 1.434(4) O(11) C(9) 1.429(4) C(1) E C(7) 105.3(1) 102.2(1) 95.0(1) E C(1) N(1) 126.0(1) 125.9(1) 126.4(2) E C(1) N(11) 126.3(2) C(1) N(1) C(2) 108.9(1) 109.1(2) 109.3(2) C(1) N(11) C(21) 109.5(2) N(1) C(2) C(2a) 107.2(1) 107.1(1) N(1) C(2) C(21) 107.0(3) N(11) C(21) C(2) 106.9(3) N(1) C(1) N(1a) 107.8(2) 107.8(2) N(1) C(1) N(11) 107.3(2) E C(7) C(8) 119.1(1) 119.0(1) 118.6(2) E C(7) C(81) 118.2(2) C(7) C(8) O(1) 116.2(1) 116.0(2) 116.0(3 C(7) C(81) O(11) 115.5(3) C(7) C(8) O(2) 128.2(3) C(7) C(81) O(21) 128.6(3) C(8) O(1) C(9) 118.1(1) 117.9(2) 116.8(2) C(81) O(11) C(9) 116.6(2) O(1) C(9) O(1a) 111.3(2) 110.7(2) O(1) C(9) O(11) 111.6(3) C(10) C(9) C(11) 112.0(2) 112.2(3) 113.7(3) Z. Anorg. Allg. Chem. 2003, 629, zaac.wiley-vch.de 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1543

4 N. Kuhn, A. Al-Sheikh, M. Steimann, M. Ströbele Fig. 3 View on the structure of C 17 H 26 N 2 O 4 Te (9c) in the crystal. Fig. 1 View on the structure of C 17 H 26 N 2 O 4 S(9a) in the crystal. C bond angles in 9 are in the range expected for diaryl chalcogenides [28 30] and decrease in the series S>Se>Te according to the predictions of the VSEPR model [34]. As discussed for 3, the relative orientation of the π-orbitals of the carbon atoms attached at the sulfur atom models a low lying transition state for the thiiran cyclisation [5]. In 9a and 9b, the planes of the C 3 (dioxanide) and CN 2 (imidazolium) fragments both are in perpendicular orientation, with respect to the central EC 2 plane, from reasons of crystallographic symmetry. In 9c, the corresponding interplanar angles are also far away from copanarity [C(1)Te(1)C(7)/N(1)C(1)N(11) 72.0(9), C(1)Te(1)C(7)/ C(8)C(7)C(81) 102.6(9) ]. Despite their short contact distances of C(1) and C(7) [9a 2.79(1), 9b 2.95(1), 9c 3.12(1) Å], cyclisation or chalcogen elimination from 9 could not be observed. Fig. 2 View on the structure of C 17 H 26 N 2 O 4 Se (9b) in the crystal. S-C, Se-C and Te-C bonds in their diaryl derivatives (see e.g. [28 30]). In every case, the bond lengths between E and the coordinating imidazolium carbon atom are the shorter ones [S(1)-C(1) (18), S(1)-C(7) (19); Se(1)-C(1) 1.911(2), Se(1)-C(7) 1.876(3), Te(1) C(1) 2.163(3), Te(1)-C(7) 2.070(3) Å]. As expected, we see these E-C bond lengths to be elongated on coordination of 8 [8b: Se-C 1.853(4); 8c: Te-C 2.087(4); 11: S-C 1.690(2) Å] [11,12,31] to give 9 as it has been observed for halogen adducts [14 16,32] and metal complexes [33] of 8. The C-E- Concluding Remarks As expected, the imidazolium and dioxanide fragments present in 9 cause a most effective stabilization of their zwitterionic structures. In fact, comparison of the structures of 2 and 9a indicates a stronger charge separation for the title compound, and the high thermal stability of the compounds 9 is worth to be underlined. Even the tellurium derivative 9c melts above 160 C without decomposition. Therefore, the title compounds resemble more closely to diaryl derivatives than to ylides. Stabilization of the formal charges by resonance in 9 lowers efficiently their reactivity, and we didn t succeed to observe dipolar cyclisation reactions characteristic of thiocarbonyl ylides, as yet. The influence of electrophilic attack at the chalcogen atoms on the nature of the E-C bonds is currently under invetsigation, and we will report on our results on alkylation and coordination of 9 at metal atoms in due course. Experimental Section All experiments have been performed in purified solvents under argon. 1,3-Diisopropyl-4,5-dimethyl-2-thioimidazoline (8a) [10], WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim zaac.wiley-vch.de Z. Anorg. Allg. Chem. 2003, 629,

5 Novel Zwitterionic Sulfides, Selenides and Tellurides 1,3-diisopropyl-4,5-dimethyl-2-selenoimidazoline (8b) [11], 1,3-diisopropyl-4,5-dimethyl-2-telluroimidazoline (8c) [12] and 5-bromo- 2,2-dimethyl-4,6-dioxo-1,3-dioxan (7) [22] have been obtained according to published procedures. Crystallographic data for the structural analyses have been deposited with the Cambridge Crystallographic Data Centre (9a: CCDC , 9b: CCDC , 9c: CCDC ). Copies of this information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, U.K.; Fax ; or www: General procedure for the synthesis of 9. 5 mmols of 8 were added to a solution of g (5 mmol) of 7 in 30 ml of dichloromethane, and the mixture was stirred at room temp. for 1 h. After addition of 0.90 ml (6.5 mmol) of triethylamine and stirring for further 1 h, the solution was extracted with 10 ml of water. The organic layer was dried over Na 2 SO 4 and evaporated in vacuo to dryness. The residue was recrystallized from dichloromethane to give the compounds 9 as stable colourless crystals. C 17 H 26 N 2 O 4 S (9a) g (95 %) yield, m.p. 213 C. Elemental analysis for C 17 H 26 N 2 O 4 S ( g/mol): found (calc.) C (57.60), H 7.87 (7.39), N 7.95 (7.90) %. 1 H-NMR (CDCl 3 ): δ 1.50 (d, 12 H, CHMe 2 ; 3 J 6.9 Hz), 1.54 (s, 6 H, 2- Me M ), 2.27 (s, 6 H, 4,5-Me I ), 6.11 (sept, 2 H, CHMe 2 ). 13 C-NMR (CDCl 3 ): δ 9.5 (4,5-Me I ), 20.4 (CHMe 2 ), 25.1 (2-Me M ), 51.9 (CHMe 2 ), 61.5 (C5 M ), (C2 M ), (C4,5 I ), (C4,6 M ), C2 I not observed. IR (KBr): ν CO 1649 cm 1. MS (FAB): m/z (%) 354 [16, M ], 297 [8, M 2 MeCO], 212 [100, M C 6 H 6 O 4 ] and further fragments. C 17 H 26 N 2 O 4 Se (9b) g (95 %) yield, m.p. 201 C. Elemental analysis for C 17 H 26 N 2 O 4 Se ( g/mol): found (calc.) C (50.87), H 5.89 (6.53), N 6.76 (6.98) %. 1 H-NMR (CDCl 3 ): δ 1.51 (d, 12 H, CHMe 2 ; 3 J 7.2 Hz), 1.56 (s, 6 H, 2- Me M ), 2.28 (s, 6 H, 4,5-Me I ), 6.00 (sept, 2 H, CHMe 2 ). 13 C-NMR (CDCl 3 ): δ 9.5 (4,5-Me I ), 20.4 (CHMe 2 ), 25.0 (2-Me M ), 53.7 (CHMe 2 ), 62.2 (C5 M ), (C2 M ), (C4,5 I ), (C4,6 M ), C2 I not observed. 77 Se-NMR (CDCl 3,Me 2 Se ext.): δ IR (KBr): ν CO 1643 cm 1. MS (FAB): m/z (%) 403 [24, M H], 345 [100, M 2 MeCO], 259 [68, M C 6 H 6 O 4 ] and further fragments. C 17 H 26 N 2 O 4 Te (9c) g (98 %) yield, m.p. 165 C. Elemental analysis for C 17 H 26 N 2 O 4 Te ( g/mol): found (calc.) C (45.37), H 5.53 (5.82), N 6.20 (6.23) %. 1 H-NMR (CDCl 3 ): δ 1.51 (d, 12 H, CHMe 2 ; 3 J 6.9 Hz), 1.55 (s, 6 H, 2- Me M ), 2.28 (s, 6 H, 4,5-Me I ), 5.80 (sept, 2 H, CHMe 2 ). 13 C-NMR (CDCl 3 ): δ 9.6 (4,5-Me I ), 20.4 (CHMe 2 ), 24.9 (2-Me M ), 51.2 (CHMe 2 ), 57.0 (C5 M ), (C2 M ), (C4,5 I ), (C4,6 M ), C2 I not observed. 125 Te-NMR (CDCl 3 at -46 C, Me 2 Te ext.): δ IR (KBr): ν CO 1637 cm 1. MS (FAB): m/z (%) 452 [8, M H], 393 [68, M 2 MeCO], 307 [56, M C 6 H 6 O 4 ], 181 [100, M C 6 H 6 O 4 Te] and further fragments. This work has been supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. We are indebted to Prof. Dr. Roland Boese (Essen) for helpful discussions and to Prof. Dr. H.-Jürgen Meyer (Tübingen) for providing his X-ray facilities. References [1] Meldrum s acid derivatives 4. For part 3 of this series see N. Kuhn, A. Al-Sheikh, M. Steimann, Z. Naturforsch. 2003, 58b, 481. [2] W. J. Middleton, J. Org. Chem. 1966, 31, 3731; S. 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