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Organoselenium compounds with N,C,N pincer groups. Synthesis, structure and reactivity
Polyhedron 160 (2019) 279–285
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Organoselenium compounds with N,C,N pincer groups. Synthesis, structure and reactivity Alexandra Pop, Anca Silvestru ⇑ Centre of Supramolecular Organic and Organometallic Chemistry, Department of Chemistry, Faculty of Chemistry and Chemical Engineering, Babesß-Bolyai University, Str. Arany Janos 11, RO-400028 Cluj-Napoca, Romania
a r t i c l e
i n f o
Article history: Received 8 November 2018 Accepted 21 December 2018 Available online 30 December 2018 Keywords: Pincer ligands Intramolecular interactions Ionic species Dynamic solution behavior Crystal and molecular structure
a b s t r a c t The new diorganodiselenides [2,6-{E(CH2CH2)2NCH2}2C6H3]2Se2 (E = MeN, O) with N,C,N pincer groups were oxidized with SO2Cl2 to the corresponding organoselenium(II) chlorides of type [2,6-{E (CH2CH2)2NCH2}2C6H3]SeCl. The new chlorides, as well as the related [2,6-(Me2NCH2)2C6H3]SeCl, transfer easily the chlorine atom to [AuCl(tht)] (tht = tetrahydrothiophene), thus forming ionic species based on the organoselenium cations [2,6-{E(CH2CH2)2NCH2}2C6H3Se]+ or [2,6-(Me2NCH2)2C6H3Se]+ and the [AuCl2] anion. The reaction between [2,6-(Me2NCH2)2C6H3]2Se2 and [(C6F5)Au(tht)] resulted in an ionic species as well, i.e. [2,6-(Me2NCH2)2C6H3Se]+[Au(C6F5)2]. The room temperature 1H NMR spectra suggest a fast dynamic behavior in solution for all species, except the ionic [2,6-{O(CH2CH2)2NCH2}2C6H3Se]+Cl and [2,6-(Me2NCH2)2C6H3Se]+[Au(C6F5)2], for which the 1H NMR resonances in the aliphatic region suggest that both N?Se intramolecular interactions are preserved in solution. The solid state structures of {[2,6-{O(CH2CH2)2NCH2}2C6H3Se]+Cl}H2O, [2,6-(Me2NCH2)2C6H3Se]+[AuCl2] and [2,6(Me2NCH2)2C6H3Se]+[Au(C6F5)2] were established by single-crystal X-ray diffraction. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction Organoselenium compounds attracted a continuous interest over the last decades owing to their biological and technical importance [1–3]. They found valuable applications in organic synthesis, either as catalysts or transfer reagents [4], in biochemistry [5], or as precursors for electronic materials [6]. The specific behaviour of selenium is better understood by taking into account its participation in nonbonding interactions, as either a donor or an acceptor partner [7,8]. In both cases, a stable T-shaped coordination geometry is realized about selenium. It was observed that organic groups with side arms bearing donor heteroatoms (O, N) stabilize low oxidation states of main group elements [9]. The intramolecular coordination of such a side-arm is responsible for the increased hydrolytic and thermal stability of main group metal organoselenolates as well [10]. Different species, including diorganodiselenides, organoselenium halides and diorganoselenides, bearing C,N-chelating groups, e.g. 2-(R1R2NCH2)C6H4 (R1 = Cy, R2 = Me, R1 = R2 = Me, Et, Pri) or 2-E(CH2CH2)2NCH2C6H4, were reported and investigated both at experimental and theoretical level [11]. It was observed that the intramolecular N?Se interaction induces
⇑ Corresponding author. E-mail address: [email protected] (A. Silvestru). https://doi.org/10.1016/j.poly.2018.12.041 0277-5387/Ó 2019 Elsevier Ltd. All rights reserved.
improved biological and catalytic properties, e.g. diorganodiselenides of type [2-(R2NCH2)C6H4]2Se2 (R = Me, Pri) used as synthetic models for the glutathione peroxidase proved a better antioxidant activity in comparison with the species without such interactions [12]. The reported data related to organoselenium compounds containing aryl groups with two pendant arms capable for intramolecular N?Se coordination are so far limited to few species bearing the (N,C,N) pincer ligand 2,6-(Me2NCH2)2C6H3, e.g. [2,6-(Me2NCH2)2C6H3]2Se2 [13], [2,6-(Me2NCH2)2C6H3]SeR (R = Me, n-octyl) [14] and several ionic species of type [2,6-(Me2NCH2)2C6H3Se]+X (X = Cl, Br, I [15], PF6 [14,16], HF2, OSO2CF3 [16]. Recently we have shown also that [2,6-(Me2NCH2)2C6H3Se] Cl in reaction with organoantimony or -bismuth halides of type R’2MCln (R0 = 2-(Me2NCH2)C6H4, n = 1, M = Sb, Bi; R0 = Ph, n = 1, 3, M = Sb) led to the ionic species [2,6-(Me2NCH2)2C6H3Se]+[R0 2MCln+1] [15]. On the other hand, gold organochalcogenolates, mainly the thiolates, are important for their applications in medicine, as antiarthritic, anti-tumoral or anti-HIV reagents [17], or in nanoscience, not only as luminescent species [18], but also as precursors for other materials with specific electronic properties, or as stabilizers for metal nanoparticles [19]. Anyway, the chemistry of gold organoselenolates was not so deeply explored, even if the soft gold is expected to have a significant affinity for the soft selenium. Mononuclear ([Au{SeC 6 H 4 (CH 2 NMe 2 )-2}(PR 3 )] (PR 3 = PPh 3 ,
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PPh2py) and dinuclear [Au2{SeC6H4(CH2NMe2)-2}2(l-P-P)] gold(I) complexes were obtained by reacting [AuCl(PR 3 )] or [Au 2 Cl 2 ( l -P-P)] (P-P = bis(diphenylphosphino)methane, bis (diphenylphosphino)ethane, 1,1 0 -bis(diphenylphosphino)ferrocene) with MSe[C6H4(CH2NMe2)-2] (M = Li, K) [17a]. Several gold species containing the metal directly attached to a C,N-chelating 2-(Me2NCH2)C6H4 or the pincer N,C,N ligand 2,6-(Me2NCH2)2C6H3 were reported as well, e.g. the dinuclear [{2-(Me2NCH2)C6H4}Au]2, [{2,6-(Me2NCH2)2C6H3}Au]2 and the mononuclear [{2,6-(Me2NCH2)2C6H3}Au(PPh3)]. Such gold(I) complexes were observed to transfer easily the organic groups attached to gold to different d metals (Ti, Fe) [20]. As a continuation of our studies related to organoselenium compounds bearing organic groups with two pendant arms, we have further investigated the influence of different substituents in the pendant arms upon their solution behaviour and their reactivity towards gold(I) containing species. We report here about the new diorganodiselenides [2,6-{E(CH2CH2)2NCH2}2C6H3]2Se2 [E = MeN (1), O (2)], the corresponding organoselenium(II) chlorides [2,6-{E(CH2CH2)2NCH2}2C6H3Se]+Cl [E = MeN (3), O (4)], as well as the ionic compounds [2,6-{E(CH2CH2)2NCH2}2C6H3Se]+ [AuCl2] [E = MeN (5), O (6)], [2,6-(Me2NCH2)2C6H3Se]+[AuCl2] (7) and [2,6-(Me2NCH2)2C6H3Se]+[Au(C6F5)2] (8) based on organoselenium cations and gold(I) anions.
2.2. Synthesis 2.2.1. Synthesis of [2,6-{MeN(CH2CH2)2NCH2}2C6H3]2Se2 (1) A solution of nBuLi in hexane (2.5 mL, 1.6 M, 3.9 mmol) was added dropwise to a solution of 1-Br-2,6-[MeN(CH2CH2)2NCH2]2C6H3 (1.50 g, 3.9 mmol) in n-hexane (40 mL) at room temperature and the reaction mixture was left under stirring for 24 h. Evaporation of the solvent gave a brown oil which was dissolved in THF (40 mL). Selenium powder (0.308 g, 3.9 mmol) was added and the reaction mixture was left under stirring for other 24 h at room temperature. The resulting yellow solution was poured into a beaker containing water (10 mL) and left overnight for complete oxidation and hydrolysis. The reaction mixture was extracted several times with dichloromethane and the combined organic phases were dried over anhydrous MgSO4. Evaporation of the solvent gave the title compound as a brown oil which was subsequently purified by column chromatography on silicagel, by using n-hexane as eluent. Yield: 0.84 g, 57%. 1H NMR (CDCl3, 400 MHz): d = 7.28–7.33 (m, 2H, H3,5), 7.22–7.25 (m, 1H, H4), 3.50 (s, 4H, H7,70 ), 2.46 (br., 16H, H8-11,80 -110 ), 2.27 (s, 6H, NCH3). 13C NMR (CDCl3, 100 MHz): d = 138.27 (C1), 129.29 (C3,5), 128.29 (C2,6), 127.11 (C4), 63.15 (C7,70 ), 55.21 (C8,11,80 ,110 ), 53.16 (C9,10,90 ,100 ), 46.15 (NCH3). 77Se NMR (CDCl3, 76 MHz): d = 424.8. HRMS (ESI+), m/z (%): 381.1550 (100), [{2,6-MeN(CH2CH2)2NCH2}2C6H3Se+], calcd. for C18H29N4Se: m/z = 381.1552.
2. Experimental 2.1. Materials and methods Starting materials were commercially available and used without further purification (SO2Cl2, 2-bromo-1,3-dimethylbenzene, Nmethylpiperazine, morpholine and nBuLi) or were prepared according to literature procedures: 1-Br-2,6-[MeN(CH2CH2)2NCH2]2C6H3 [21], 1-Br-2,6-[O(CH2CH2)2NCH2]2C6H3 [22], [2,6(Me2NCH2)2C6H3]SeCl [15], [AuC6F5(tht)] and [AuCl(tht)] [23]. Organic solvents were dried and distilled under argon by following standard procedures prior to use. Experiments involving air sensitive compounds were performed under argon atmosphere. Elemental analyses were made on a Flash EA 1112 analyzer. Melting points were measured on an Electrothermal 9200 apparatus. 1H, 13 C, 19F and 77Se NMR spectra were recorded in CDCl3 at room temperature on a Bruker 400 or 600 MHz spectrometer. The chemical shifts are reported in d units (ppm) relative to TMS (1H and 13C), CFCl3 (19F) and Me2Se (77Se). The NMR data were processed using the MestReNova software [24]. The assignments of the 1H and 13 C chemical shifts are based on 2D NMR correlation experiments (COSY, HSQC and HMBC) and are given according to the numbering depicted in Scheme 1. ESI mass spectra were recorded using a Thermo Scientific LTQOrbitrapXL instrument equipped with a standard ESI/APCI source.
2.2.2. [2,6-{O(CH2CH2)2NCH2}2C6H3]2Se2 (2) [2,6-{O(CH2CH2)2NCH2}2C6H3]2Se2 (2) was obtained similarly with 1, as a brown oil, from nBuLi in hexane (1.98 mL, 1.6 M, 3.18 mmol), 1-Br-2,6-[O(CH2CH2)2NCH2]2C6H3 (1.13 g, 3.18 mmol) and selenium powder (0.25 g, 3.18 mmol). Yield: 0.83 g, 73%. 1H NMR (CDCl3, 400 MHz): d = 7.35–7.38 (m, 2H, H3,5), 7.22–7.25 (m, 1H, H4), 3.69–3.72 (m, 8H, H8,11,80 ,110 ), 3.50 (s, 4H, H7,70 ), 2.45 (br, 8H, H9,10,90 ,100 ). 13C NMR (CDCl3, 100 MHz): d = 137.85 (C1), 129.31 (C3,5), 128.36 (C2,6), 127.25 (C4), 67.09 (C8,11,80 ,110 ), 63.57 (C7,70 ), 53.72 (C9,10,90 ,100 ). 77Se NMR (CDCl3, 76 MHz): d = 400.1. HRMS (ESI+ ), m/z (%): 355.0913 (100) [2,6-{O(CH2CH2)2NCH2}2C6H3Se+], calcd. for C16H23N2O2Se: m/z = 355.0919. 2.2.3. Synthesis of [2,6-{MeN(CH2CH2)2NCH2}2C6H3Se]+Cl (3) A solution of sulfuryl chloride (0.483 g, 3.6 mmol) in toluene (20 mL) was added dropwise to a solution of [2,6-{MeN(CH2CH2)2NCH2}2C6H3]2Se2 (1) (2.75 g, 3.6 mmol) in toluene (10 mL) under stirring. The reaction mixture was stirred over night at room temperature. The resulting solid was filtered off and solubilized in dichloromethane. The obtained solution was washed with a NaOH 5 M aqueous solution (20 mL), separated and dried over Na2SO4. After removing the solvent, a pale yellow solid was obtained. Yield: 2.00 g, 66%. M.p. 192 °C. Anal. Calc. for C18H29ClN4Se (MW = 415.86): C, 51.99; H, 7.03; N, 13.47. Found: C, 51.63; H
Scheme 1. Numbering scheme for NMR assignments in compounds 1–8.
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6.95; N, 13.54%. 1H NMR (CDCl3, 600 MHz): d = 7.20–7.34 (m, 6H, H3-5), 3.52 (s, 4H, H7,70 ), 2.56 (br, 16H, H8-11,80 -110 ), 2.36 (s, 6H, NCH3). 13C NMR (CDCl3, 150 MHz): d = 137.71 (C1), 129.16 (C2,6), 128.24 (C3,5), 127.16 (C4), 62.71 (C7,70 ), 54.78 (C9,10,90 ,100 ), 52.21 (C8,11,80 ,110 ), 45.47 (NCH3). 77Se NMR (CDCl3, 57.24 MHz): d = 1198. ESI+ MS, m/z (%): 381.15 (100), [2,6-{MeN (CH2CH2)2NCH2}2C6H3Se+]. 2.2.4. [2,6-{O(CH2CH2)2NCH2}2C6H3Se]+Cl (4) Similarly with 3, as a pale yellow solid, from [2,6-{O(CH2CH2)2NCH2}2C6H3]2Se2 (2) (1.19 g, 1.68 mmol) and sulfuryl chloride (0.227 g, 1.68 mmol). Yield: 0.70 g (53.4 %). M.p. 185 °C. Anal. Calc. for C16H23N2O2SeCl (MW = 389.78): C, 49.30; H, 5.95; N, 7.19. Found: C, 49.72; H, 6.18; N, 7.12%. 1H NMR (CDCl3, 600 MHz): d = 7.62–7.64 (m, 1H, H4), 7.40–7.42 (m, 2H, H3,5), 4.25 (AB spin system with dA 4.24 and dB 4.26, 2JHH 5.23 Hz, 4H, H7,70 ), 4.21 (dt, 2 JHpro-cis,Hpro-trans 13.2, 3JHpro-cis,Hpro-trans 2.9 Hz, 4H, pro-cisH9,90 ,10,100 ), 3.89 (dd, 2JHpro-cis,Hpro-trans 13.0, 3JHpro-cis,Hpro-trans 3.5 Hz, 4H, pro-trans-H9,90 ,10,100 ), 3.34 (d, 2JHpro-cis,Hpro-trans 12.1 Hz, 4H, procis-H8,80 ,11,110 ), 2.92 (dt, 2JHpro-cis,Hpro-trans 12.4, 3JHpro-cis,Hpro-trans 3.7 Hz, 4H, pro-trans-H8,80 ,11,110 ). 13C NMR (CDCl3, 150 MHz): d = 131.68 (C4), 130.37 (C2,6), 129.42 (C3,5), 127.53 (C1), 63.63 (C8,80 ,11,110 ), 61.18 (C7,70 ), 51.39 (C9,90 10,100 ). 77Se NMR (CDCl3, 57.24 MHz): d = 655. ESI+ MS, m/z (%): 355.10 (100) [2,6-{O (CH2CH2)2NCH2}2C6H3Se+]. 2.2.5. Synthesis of [2,6-{MeN(CH2CH2)2NCH2}2C6H3Se]+[AuCl2] (5) AuCl(tht) (0.074 g, 0.23 mmol) was added to a solution of 2,6[MeN(CH2CH2)2NCH2]2C6H3SeCl (3) (0.097 g, 0.23 mmol) in dichloromethane (15 mL), at room temperature, under stirring. After 2 h the solvent was removed in vacuum and the resulting pale yellow precipitate was washed with Et2O. Yield: 0.098 g (65%), M.p. 216 °C. Anal. Calc. for C18H29AuCl2N4Se (MW = 648.28): C, 33.35; H, 4.51; N, 8.64. Found: C, 33.74; H, 4.61; N, 8.72%; 1H NMR (CDCl3, 600 MHz): d = 7.25–7.37 (m, 3H, H3-5), 3.68 (s, 4H, H7,70 ), 3.35–3.56 (br., 8H, H8,11,80 ,110 ), 2.91 (br., 8H, H9,90 ,10,100 ), 2.84 (s, 6H, CH3). 13C NMR (CDCl3, 150 MHz): d = 135.42 (C1), 129.50 (C2,6), 128.79 (C3,5), 128.29 (C4), 61.82 (C7,70 ), 49.63 (C8,11,80 ,110 ), 44.05 (NCH3), 40.32 (C9,90 ,10,100 ). The 77Se resonance could not be detected. ESI+ MS, m/z (%): 381.15 (100), [2,6-{MeN(CH2CH2)2NCH2}2C6H3Se+]. ESI- MS m/z (%): 266.91 (100) [AuCl 2 ]. 2.2.6. [2,6-{O(CH2CH2)2NCH2}2C6H3Se]+[AuCl2] (6) Similarly with 5, from AuCl(tht) (0.083 g, 0.25 mmol) and 2,6-[O (CH2CH2)2NCH2]2C6H3SeCl (4) (0.100 g, 0.25 mmol), as a pale yellow solid. Yield: 0.125 g (78.6%), M.p. 81 °C. Anal. Calc. for C16H23AuCl2N2O2Se (MW = 622.20): C, 30.89; H, 3.73; N 4.50. Found: C, 30.74; H, 3.56; N, 4.42%. 1H NMR (CDCl3, 600 MHz): d = 7.62–7.66 (m, 1H, C6H3), 7.38–7.43 (m, 2H, C6H3), 4.27 (s, 4H, H7,70 ), 4.17 (t, 2 JHH = 12.2 Hz, 4H, pro-trans-H8,11,80 ,110 ), 3.91 (d, 2JHH = 12.9 Hz, 4H, pro-cis-H8,11,80 ,110 ), 3.35 (d, 2JHH = 12.2 Hz, 4H, pro-trans-H9,10,90 ,100 ), 2.97 (t, 2JHH = 10.2 Hz, 4H, pro-cis-H9,10,90 ,100 ). 13C NMR (CDCl3, 150 MHz): d = 131.70 (C2,6), 130.39 (C4), 129.43 (C3,5), 127.50 (C1), 63.65 (C8,11,80 ,110 ), 61.23 (C7,70 ), 51.49 (C9,10,90 ,100 ). The 77Se resonance could not be detected. ESI+ MS m/z (%): 355.09 (42) [2,6-{O(CH2CH2)2NCH2}2C6H3Se+], 268.02 (100) [{2,6-O(CH2CH2)2NCH2}2C6H3Se+ O(CH2CH2)2N]. ESI– MS, m/z (%): 266.91 (100) [AuCl 2 ]. 2.2.7. [2,6-(Me2NCH2)2C6H3Se]+[AuCl2] (7) Similarly with 5, from AuCl(tht) (0.084 g, 0.26 mmol) and [2,6(Me2NCH2)2C6H3]SeCl (0.081 g, 0.26 mmol), in CHCl3 (20 mL), as an orange solid. Yield: 0.121 g, 86 %, M.p. 136 °C. Anal. Calc. for C12H19AuCl2N2Se (MW = 538.13): C, 26.78; H, 3.56; N, 5.21. Found: C, 26.81; H, 3.72; N, 5.28%. 1H NMR (CDCl3, 600 MHz): d = 7.27– 7.30 (m, 3H, H3-5), 4.11 (s, 4H, H7,70 ), 2.96 (s, 12H, NCH3). 13C
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NMR (CDCl3, 150 MHz): d = 132.88 (C1), 132.25 (C2,6), 128.55 (C4), 126.02 (C3,5), 64.28 (C7,70 ), 49.14 (NCH3). The 77Se resonance was not observed. ESI+ MS, m/z (%): 271.07 (100) [2,6-(Me2NCH2)2C6H3Se+]; ESI- MS, m/z (%): 266.90 (100) [AuCl 2 ], 503.01 (74) [2,6(Me2NCH2)2C6H3SeAuCl]. 2.2.8. Synthesis of [2,6-(Me2NCH2)2C6H3Se]+[Au(C6F5)2] (8) (C6F5)Au(tht) (0.150 g, 0.33 mmol) was added to a solution of [2,6-(Me2NCH2)2C6H3]2Se2 (0.087 g, 0.16 mmol) in dichloromethane (15 mL), at room temperature, under stirring. After 30 minutes a black precipitate was formed and it was filtered off. From the clear solution the solvent was removed at reduced pressure and the remained yellow solid was washed with cold hexane. Yield: 0.08 g, 60%, M.p. 136 °C. Anal. Calc. for C24H19AuF10N2Se (MW = 801.33): C, 35.97; H, 2.39; N, 3.50. Found: C, 35.71; H, 2.48; N, 3.27%. 1H NMR (CDCl3, 400 MHz): d = 7.28 (t, 3JHH 7.5 Hz, 1H, H4), 7.18 (d, 3JHH 7.4 Hz, 2H, H3,5), 4.00 (s, 4H, H7,70 ), 2.87 (s, 12H, NCH3). 13C NMR (CDCl3, 100 MHz): d = 149.00 (ddm, 1JFC 223.8 Hz, 2JFC 26.7 Hz, C6F5-ortho). 143.56 (C1), 137.62 (dm, 1JFC 246.3 Hz, C6F5-para), 137.16 (dm, 1JFC 250.2 Hz, C6F5-meta), 132.06 (C2,6), 128.29 (C4), 126.03 (C3,5), 64.35 (C7,70 ), 49.10 (NCH3). The 13C resonance for C6F5-ipso could not be unambigu19 ously assigned. F NMR (CDCl3, 376 MHz): d = 114.87 115.02 (m, 4F, AuC6F5-ortho), 161.59 (t, 2F, 3JFF 21.12 Hz, AuC6F5-para), 163.20 163.41 (m, 4F, AuC6F5-meta). 77 Se NMR (CDCl3, 76 MHz): d = 1208. ESI+ MS, m/z (%): 271.07 (100) [2,6-(Me2NCH2)2C6H3Se+]; ESI- MS, m/z (%): 530.94 (100) [Au(C6F5) 2 ]. 2.3. Crystal structure determination Single crystals of 4H2O were obtained from methylene dichloride/n-hexane (1:3, by volume) and those of 7 and 8 from a mixture of acetone and Et2O (1:3, by volume). The details of the crystal structure determination and refinement are given in the Supplementary Information (SI), Table S1. Data were collected on a Bruker SMART APEX diffractometer, by using graphitemonochromated Mo Ka radiation (k = 0.71073 Å). The crystals were attached on cryoloops to a glass fiber and data were collected at room temperature (297 K). The structures were refined with anisotropic thermal parameters. The hydrogen atoms H17 and H18 of the water molecule in 4H2O were located in a difference Fourier map and they were freely refined. All the other hydrogen atoms were refined with a riding model and a mutual isotropic thermal parameter. For structure solving and refinement the software package SHELXL-2014 was used [25]. The drawings were created with the Diamond program [26]. Intermolecular contacts were found in PLATON [27]. 3. Results and discussion 3.1. Synthesis The diorganodiselenides [2,6-{E(CH2CH2)2NCH2}2C6H3]2Se2 [E = MeN (1), O (2)] were prepared by a succession of reactions, involving lithiation of the corresponding 1-Br-2,6-{E(CH2CH2)2NCH2}2C6H3, selenium insertion into the new formed carbon– lithium bond, oxidation and hydrolysis of the lithium organoselenolate, as depicted in Scheme 2, similarly with the procedure reported previously for the diorganodiselenide [2,6-(Me2NCH2)2C6H3]2Se2 [15]. Further oxidation of the diorganodiselenides 1 and 2 with SO2Cl2 resulted in the corresponding organoselenium chlorides 3 and 4, respectively. These were subsequently used in reactions with [AuCl(tht)], when the ionic organoselenium dichloroaurates 5 and 6 were obtained in moderate yields, as pale
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Scheme 2. Synthesis of compounds 1–8.
yellow solids. Similarly, the reaction between [2,6-(Me2NCH2)2C6H3Se]+Cl and [AuCl(tht)] resulted in [2,6-(Me2NCH2)2C6H3Se]+ [AuCl2] (7), while [2,6-(Me2NCH2)2C6H3Se]+[Au(C6F5)2] (8) was obtained by reacting the diorganodiselenide [2,6-(Me2NCH2)2C6H3]2Se2 with [(C6F5)Au(tht)] in a 1:2 molar ratio. We observed previously that the diorganodiselenide with one pendant arm [2(Me2NCH2)2C6H4]2Se2 give a ligand exchange reaction with [Sn{N (SiMe3)2}2], while Ph2Se2 oxidizes Sn(II) to Sn(IV) in the reaction with Sn(II) bis amide [28]. The formulation of all new compounds is supported by elemental analysis, mass spectrometry and NMR spectroscopy (1H, 13C, 19F and 77Se). 3.2. Spectroscopic characterization The room temperature NMR spectra of the diorganodiselenides 1 and 2, as well as the organoselenium chlorides 3 and 4 are consistent with the presence of only one species in solution, with equivalent pendant arms attached to the C6H3 rings. In these species, except compound 4, the 1H NMR resonance for the equivalent H7 and H70 protons (CH2N, for numbering see Scheme 1) appears as one sharp singlet. The methylene protons in the methylpiperazinyl group, both in 1 and 3, give rise to a broad 1H NMR resonance, while the methyl groups are sharp singlets (see SI, Fig. S1). The broad resonance corresponding to the methylene MeN(CH2CH2)2 protons suggest close d values for the non-equivalent protons H8,11/H80 ,110 and H9,10/H90 ,100 respectively, in the two pendant arms, as well as a fast conformation inversion of the piperazinyl six membered ring, resulting in the equivalence of the protons in equatorial and axial positions. Moreover, the 1H NMR spectra for compounds 1 and 3 suggest either the absence of any N?Se intramolecular coordination or a very fast dynamic behaviour in solution, involving decoordination of nitrogen, rotation around the C7/70 –N bonds, pyramidal inversion at nitrogen, recoordination and conformation inversion of the sixmembered rings (see SI, Fig. S2). A similar behaviour was previously observed for the proligand 1,3-[MeN(CH2CH2)2NCH2]2C6H4 [29]. The non-equivalent H8,11/H80 ,110 and H9,10/H90 ,100 protons in 2
give two multiplet resonances (see SI, Fig. S3), similarly with the situation found in the 1H NMR spectra of 1,3-[O(CH2CH2)2NCH2]2C6H4 [30], or the related one pendant arm species [2-{O(CH2CH2)2NCH2}C6H4]2Se2 [11]. This behaviour suggests, again, either the absence of any N?Se intramolecular interaction or a very weak N?Se interaction which allows the dynamic behaviour described above for compounds 1 and 3. By contrast, the methylene protons in the six membered morpholinyl rings of 4 show four distinct multiplet resonances (see SI, Fig. S3), assigned to the non-equivalent pro-cis (Ha and Hc in Scheme 1) and respectively pro-trans (Hb and Hd in Scheme 1) protons, designated like this by considering the position of the Se atom in relation with the morpholinyl rings. In this case the conformation change of the six-membered rings is much slower and the resonances of the non-equivalent equatorial and axial protons, respectively, are observable at the NMR time scale. Such a behaviour of compound 4 is possible only if the intramolecular N?Se coordination of both arms is preserved in solution at room temperature and any fast dynamic behaviour (see SI, Fig. S2) is absent. The 1H NMR spectra of compounds 5 and 6 suggest the equivalence of the two pendant arms in solution as well. By contrast with the chloride 3, the cation in 5 presents two multiplet resonances for the non-equivalent H8,11/H80 ,110 and H9,10/H90 ,100 protons, while in case of compound 6 a similar pattern as for compound 4, showing four different resonances for the nonequivalent pro-cis and pro-trans H8,11/H80 ,110 and H9,10/H90 ,100 protons was observed, thus confirming the existence of the N?Se interactions in solution at room temperature at least for compound 6, while in case of compound 5 we assume very labile N?Se interactions. For compounds 7 and 8 the singlet resonances corresponding to the H7 and the N(CH3)2 protons indicate either no intramolecular N?Se interaction or a very weak one, which determines a fluxional behaviour at room temperature. The 77Se{H} NMR resonances of 1 and 2 are located around 400 ppm, as expected for diorganodiselenides, while the 77Se{H} NMR resonances of the organoselenium chlorides are strongly low field shifted (d = 1198 ppm for 3 and 655 ppm for 4). The 77 Se NMR resonance could not be observed for compounds 5–7,
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but for compound 8 it is located at 1208 ppm, thus confirming the ionic nature of this species in solution. The 19F NMR spectrum of compound 8 shows the expected multiplet resonances for the ortho, meta and para fluorine atoms in the two C6F5 equivalent groups. The 13C{H} NMR spectra show the expected singlet resonances in the aliphatic and the aromatic regions for the organic groups attached to selenium. The 13C NMR resonances given by the C6F5 groups appear as doublets of multiplets due to the 19F–13C couplings, with large 1JFC coupling constants (range 223–249 Hz), similarly with the 13C NMR spectrum of the starting [(C6F5)Au(tht)] (see SI, Fig. S4). The ESI+ mass spectra show in all cases the organoselenium cation, [2,6-{E(CH2CH2)2NCH2}2C6H3Se+] or [2,6-(Me2NCH2)2C6H3Se+] as base peak. For the gold complexes the ESI- mass spectra show the [AuCl 2 ] and the [Au(C6F5)2 ] anions at m/z = 266.90 and 530.94, respectively, as base peaks. 3.3. Single-crystal X-ray diffraction studies
Fig. 2. Thermal ellipsoids representation at 30% probability for RN1,RN10 -7. Hydrogen atoms are omitted for clarity.
The molecular structures of 4H2O, 7 and 8, with the corresponding atom numbering schemes, are shown in Figs. 1–3, respectively, and selected interatomic distances and angles are listed in Table 1. All three compounds are ionic species, containing the cation [2,6-{O(CH2CH2)2NCH2}2C6H3Se]+ in 4H2O and [2,6(Me2NCH2)2C6H3Se]+ in 7 and 8, respectively. The three structures display several common features: – in each cation, both nitrogen atoms in the pendant arms are intramolecularly coordinated to selenium, thus resulting in 10-Se-3 species [31] with a distorted T-shaped (N,C,N)Se core with N–Se–N angles of 161.58(7)° in 4H2O, 161.8(3)° in 7, and 161.9(2)° in 8, respectively. The strong N?Se intramolecular interactions [2.2489(19)/2.1706(19) Å in 4H2O, 2.174(5) Å in 7 and 2.171(4)/2.179(6) Å in 8] are close to those found in the ionic species [{2,6-(Me2NCH2)2C6H3}Se]+ClH2O [2.183(2) and 2.184(2) Å] [15], [{2,6-(Me2NCH2)2C6H3}Se]+BrH2O [2.181(3) and 2.185(3) Å] [32] or [{2,6-(Me2NCH2)2C6H3}Se]+[Ph2SbCl4] [2.178(3) and 2.160(3) Å] [15] and well below the sum of the van der Waals radii of the two elements [RrvdW(N, Se) 3.54 Å] [33]. The difference between the two N?Se distances in 4H2O might be explained by a slightly unbalanced 3c–4e N?Se(C)–N system with the nitrogen atom of one pendant arm acting as a donor towards the Se–N acceptor moiety which include the nitrogen atom of the other arm of the pincer
Fig. 3. Thermal ellipsoids representation at 30% probability for RN1,RN2-8. Hydrogen atoms are omitted for clarity.
Table 1 Selected interatomic distances (Å) and angles (deg.) in compounds 4H2O, 7a and 8.
C(1)–Se(1) N(1)–Se(1) N(2)/N(10 )–Se(1) Au(1)–Cl(1)/Cl(10 ) N(1)–Se(1)–N(2)/N(10 ) C(1)–Se(1)–N(1) C(1)–Se(1)–N(2)/N(10 ) Cl(1)–Au(1)–Cl(10 ) C(13)–Au(1)–C(19) a
Fig. 1. Thermal ellipsoids representation at 30% probability for RN1,SN2-4H2O. Water molecule and hydrogen atoms are omitted for clarity.
4H2O
7
8
1.894(2) 2.2489(19) 2.1706(19)
1.866(9) 2.174(5) 2.174(5) 2.236(3) 161.8(3) 80.89(15) 80.89(16) 178.3(2)
1.889(9) 2.171(4) 2.179(6)
161.58(7) 80.08(9) 81.51(9)
161.9(2) 80.80(3) 81.12(3) 178.09(3)
Symmetry equivalent atoms (1 x, y, 0.5 z) in 7 are given by ‘‘prime”.
ligand, as we observed both at experimental and theoretical level (DFT calculations) for the related species [{2,6-(Me2NCH2)2C6H3}Se]+X (X = Cl, Br, I) [15]; – the two five-membered rings formed in each cation by the intramolecular N?Se coordination are not planar, but folded about an imaginary carbon-selenium axis, with the nitrogen atoms out of the residual C3Se plane: N1/N2 at 0.55/0.58 Å above and below the C1C2C7Se1 and C1C6C12Se1 planes, respectively, in 4H2O, N1/N10 at 0.55 Å above the C1C2C5Se1/ C1C20 C50 Se1 planes in 7 and N1/N2 at 0.56/0.54 Å above and below the C1C2C7Se1 and C1C6C12Se1 planes, respectively, in 8.
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Fig. 6. Cation–anion association in the crystal of 8. F18 H7B0 2.48 Å. Symmetry equivalent position x, 1 + y, 1 + z is given by ‘‘prime”. Hydrogen atoms not involved in F H interactions are omitted for clarity.
Fig. 4. Dimeric association in 4H2O. H8B Cg0 2.95 Å. (symmetry equivalent position x, 1 y, z is given by ‘‘prime”). Hydrogen atoms not involved in intermolecular interactions are omitted for clarity.
– as a consequence of the intramolecular coordination, the two five-membered rings in each cation display planar chirality (with the aromatic ring as chiral plane and the nitrogen atom as pilot atom) [34]. The crystals of the three compounds contain racemic mixtures of RN1,SN2 and SN1,RN2 isomers in 4H2O, RN1, RN2 and SN1,SN2 isomers in 8, and RN1,RN10 and SN1,SN10 isomers in 7. The morpholinyl rings in 4H2O have a chair conformation, with the nitrogen and the oxygen atoms in apices. In the crystal of 4H2O the cations are associated in dimeric units (Fig. 4) by p C– H Arylcentroid contacts, shorter than 3.1 Å, between the C6H3 ring and a hydrogen atom in the morpholinyl group of a neighbouring cation, with a c angle between the normal to the aromatic ring and the line defined by the H atom and the Arcentroid smaller than 30° [35], namely CH8B Cg(C1–C6) 2.95 Å, c 13.24°. In the crystal lattice the Cl anions interact with the water molecules by hydrogen bonding (Cl1 H17 2.51 Å, Cl1 H18 2.64 Å vs. RrvdW(Cl,H) 3.01 Å [33]), thus giving rise to infinit polymeric chains to which are interconnected the dimeric cations by hydrogen bonding as well (H2O H3 2.46 Å vs. RrvdW(O,H) 2.60 Å [33], see SI, Fig. S5). The so formed layers are further connected in a 3D supramolecular network by additional Cl H interactions (Cl1 H12B 2.76 Å, see SI, Fig. S6). In compound 7 weak Cl H contacts are established between the [AuCl2] anions and the organoselenium cations. Each chlorine atom in the anions participate in three such contacts, involving
hydrogen atoms in the pendant arms of the cations. Polymeric chains are formed with the participation of the same chlorine atom in the anion and hydrogens of the pendant arms of the neighbouring cations (Cl1 H5B 2.79 Å and Cl1 H7B 2.83 Å), as depicted in Fig. 5. The third Cl H contact (Cl1 H6C 2.94 Å) is established between the as formed chains, thus leading to a layered 2D network (see SI, Fig. S7). No further contacts between these layers are present. The crystal of 8 has a layered structure as well, built by weak F H contacts established between the [Au(C6F5)2] anions and the organoselenium cations. Each anion participates with four fluorine atoms in such interactions, three of them belonging to the same C6F5 group, and the fourth to the other one. A cation–anion unit showing the F H interactions involved in the construction of the extended 2D network is depicted in Fig. 6. The three fluorine atoms in the same C6F5 group (F16 H11C 2.61 Å, F17 H10B 2.59 Å and F18 H7B 2.48 Å, vs. RrvdW(H,F) 2.67 Å [33]) interact with hydrogen atoms in the two pendant arms of the cations, while the fluorine atom in the other C6F5 group of the anion (F23 H4 2.62 Å) interact with the C6H3-para hydrogen atom (see SI, Fig. S8). 4. Conclusions In solution, for all compounds was observed the equivalence of the two pendant arms in the pincer N,C,N ligand. The 1H NMR spectra provided evidences that the N?Se intramolecular coordination observed in solid state is preserved in solution at room temperature as well only for compound 4, for which four distinct multiplet resonances, assigned to the non-equivalent pro-cis and respectively pro-trans protons in the morpholinyl ring were noticed. For the methylpiperazinyl substituted aryl groups in compounds 1, 3 and
Fig. 5. Polymeric chain in compound 7. Cl1a H7B 2.83 Å, Cl1a H5Bb 2.79 Å. Symmetry equivalent positions 0.5 x, 0.5 y, 1 z and x, 1 y, 1 z are given by ‘‘a” and ‘‘b”, respectively. Hydrogen atoms not involved in Cl H interactions are omitted for clarity.
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5 the broad resonances in the aliphatic region suggest a fast conformation change of the MeN(CH2CH2)2N moiety. Except compound 4, for which an AB spin system was observed, the resonance corresponding to the H7,70 protons in the CH2N moiety appears as a sharp singlet, due to a dynamic process involving decoordination, inversion at nitrogen and recoordination to selenium, too fast to be observed at room temperature. The cations [2,6-{O(CH2CH2)2NCH2}2C6H3Se]+ in 4H2O and [2,6(Me2NCH2)2C6H3Se]+ in 7 and 8 exhibit in solid state a T-shaped CSeN2 core (10–Se–3 hypercoordinated species) and we assume for all the other ionic compounds described in this paper a similar behaviour in solid state. Funding information Financial support from the National University Research Council of Romania (Research Project PNII-ID 0659/2011) is greatly appreciated. A. Pop is grateful for the financial support from Babeș-Bolyai University, Romania (Research project GTC31809/23.03.2016).
[11]
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Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.poly.2018.12.041.
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Organoselenium compounds with N,C,N pincer groups. Synthesis, structure and reactivity Alexandra Pop, Anca Silvestru ⇑ Centre of Supramolecular Organic and Organometallic Chemistry, Department of Chemistry, Faculty of Chemistry and Chemical Engineering, Babesß-Bolyai University, Str. Arany Janos 11, RO-400028 Cluj-Napoca, Romania
a r t i c l e
i n f o
Article history: Received 8 November 2018 Accepted 21 December 2018 Available online 30 December 2018 Keywords: Pincer ligands Intramolecular interactions Ionic species Dynamic solution behavior Crystal and molecular structure
a b s t r a c t The new diorganodiselenides [2,6-{E(CH2CH2)2NCH2}2C6H3]2Se2 (E = MeN, O) with N,C,N pincer groups were oxidized with SO2Cl2 to the corresponding organoselenium(II) chlorides of type [2,6-{E (CH2CH2)2NCH2}2C6H3]SeCl. The new chlorides, as well as the related [2,6-(Me2NCH2)2C6H3]SeCl, transfer easily the chlorine atom to [AuCl(tht)] (tht = tetrahydrothiophene), thus forming ionic species based on the organoselenium cations [2,6-{E(CH2CH2)2NCH2}2C6H3Se]+ or [2,6-(Me2NCH2)2C6H3Se]+ and the [AuCl2] anion. The reaction between [2,6-(Me2NCH2)2C6H3]2Se2 and [(C6F5)Au(tht)] resulted in an ionic species as well, i.e. [2,6-(Me2NCH2)2C6H3Se]+[Au(C6F5)2]. The room temperature 1H NMR spectra suggest a fast dynamic behavior in solution for all species, except the ionic [2,6-{O(CH2CH2)2NCH2}2C6H3Se]+Cl and [2,6-(Me2NCH2)2C6H3Se]+[Au(C6F5)2], for which the 1H NMR resonances in the aliphatic region suggest that both N?Se intramolecular interactions are preserved in solution. The solid state structures of {[2,6-{O(CH2CH2)2NCH2}2C6H3Se]+Cl}H2O, [2,6-(Me2NCH2)2C6H3Se]+[AuCl2] and [2,6(Me2NCH2)2C6H3Se]+[Au(C6F5)2] were established by single-crystal X-ray diffraction. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction Organoselenium compounds attracted a continuous interest over the last decades owing to their biological and technical importance [1–3]. They found valuable applications in organic synthesis, either as catalysts or transfer reagents [4], in biochemistry [5], or as precursors for electronic materials [6]. The specific behaviour of selenium is better understood by taking into account its participation in nonbonding interactions, as either a donor or an acceptor partner [7,8]. In both cases, a stable T-shaped coordination geometry is realized about selenium. It was observed that organic groups with side arms bearing donor heteroatoms (O, N) stabilize low oxidation states of main group elements [9]. The intramolecular coordination of such a side-arm is responsible for the increased hydrolytic and thermal stability of main group metal organoselenolates as well [10]. Different species, including diorganodiselenides, organoselenium halides and diorganoselenides, bearing C,N-chelating groups, e.g. 2-(R1R2NCH2)C6H4 (R1 = Cy, R2 = Me, R1 = R2 = Me, Et, Pri) or 2-E(CH2CH2)2NCH2C6H4, were reported and investigated both at experimental and theoretical level [11]. It was observed that the intramolecular N?Se interaction induces
⇑ Corresponding author. E-mail address: [email protected] (A. Silvestru). https://doi.org/10.1016/j.poly.2018.12.041 0277-5387/Ó 2019 Elsevier Ltd. All rights reserved.
improved biological and catalytic properties, e.g. diorganodiselenides of type [2-(R2NCH2)C6H4]2Se2 (R = Me, Pri) used as synthetic models for the glutathione peroxidase proved a better antioxidant activity in comparison with the species without such interactions [12]. The reported data related to organoselenium compounds containing aryl groups with two pendant arms capable for intramolecular N?Se coordination are so far limited to few species bearing the (N,C,N) pincer ligand 2,6-(Me2NCH2)2C6H3, e.g. [2,6-(Me2NCH2)2C6H3]2Se2 [13], [2,6-(Me2NCH2)2C6H3]SeR (R = Me, n-octyl) [14] and several ionic species of type [2,6-(Me2NCH2)2C6H3Se]+X (X = Cl, Br, I [15], PF6 [14,16], HF2, OSO2CF3 [16]. Recently we have shown also that [2,6-(Me2NCH2)2C6H3Se] Cl in reaction with organoantimony or -bismuth halides of type R’2MCln (R0 = 2-(Me2NCH2)C6H4, n = 1, M = Sb, Bi; R0 = Ph, n = 1, 3, M = Sb) led to the ionic species [2,6-(Me2NCH2)2C6H3Se]+[R0 2MCln+1] [15]. On the other hand, gold organochalcogenolates, mainly the thiolates, are important for their applications in medicine, as antiarthritic, anti-tumoral or anti-HIV reagents [17], or in nanoscience, not only as luminescent species [18], but also as precursors for other materials with specific electronic properties, or as stabilizers for metal nanoparticles [19]. Anyway, the chemistry of gold organoselenolates was not so deeply explored, even if the soft gold is expected to have a significant affinity for the soft selenium. Mononuclear ([Au{SeC 6 H 4 (CH 2 NMe 2 )-2}(PR 3 )] (PR 3 = PPh 3 ,
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PPh2py) and dinuclear [Au2{SeC6H4(CH2NMe2)-2}2(l-P-P)] gold(I) complexes were obtained by reacting [AuCl(PR 3 )] or [Au 2 Cl 2 ( l -P-P)] (P-P = bis(diphenylphosphino)methane, bis (diphenylphosphino)ethane, 1,1 0 -bis(diphenylphosphino)ferrocene) with MSe[C6H4(CH2NMe2)-2] (M = Li, K) [17a]. Several gold species containing the metal directly attached to a C,N-chelating 2-(Me2NCH2)C6H4 or the pincer N,C,N ligand 2,6-(Me2NCH2)2C6H3 were reported as well, e.g. the dinuclear [{2-(Me2NCH2)C6H4}Au]2, [{2,6-(Me2NCH2)2C6H3}Au]2 and the mononuclear [{2,6-(Me2NCH2)2C6H3}Au(PPh3)]. Such gold(I) complexes were observed to transfer easily the organic groups attached to gold to different d metals (Ti, Fe) [20]. As a continuation of our studies related to organoselenium compounds bearing organic groups with two pendant arms, we have further investigated the influence of different substituents in the pendant arms upon their solution behaviour and their reactivity towards gold(I) containing species. We report here about the new diorganodiselenides [2,6-{E(CH2CH2)2NCH2}2C6H3]2Se2 [E = MeN (1), O (2)], the corresponding organoselenium(II) chlorides [2,6-{E(CH2CH2)2NCH2}2C6H3Se]+Cl [E = MeN (3), O (4)], as well as the ionic compounds [2,6-{E(CH2CH2)2NCH2}2C6H3Se]+ [AuCl2] [E = MeN (5), O (6)], [2,6-(Me2NCH2)2C6H3Se]+[AuCl2] (7) and [2,6-(Me2NCH2)2C6H3Se]+[Au(C6F5)2] (8) based on organoselenium cations and gold(I) anions.
2.2. Synthesis 2.2.1. Synthesis of [2,6-{MeN(CH2CH2)2NCH2}2C6H3]2Se2 (1) A solution of nBuLi in hexane (2.5 mL, 1.6 M, 3.9 mmol) was added dropwise to a solution of 1-Br-2,6-[MeN(CH2CH2)2NCH2]2C6H3 (1.50 g, 3.9 mmol) in n-hexane (40 mL) at room temperature and the reaction mixture was left under stirring for 24 h. Evaporation of the solvent gave a brown oil which was dissolved in THF (40 mL). Selenium powder (0.308 g, 3.9 mmol) was added and the reaction mixture was left under stirring for other 24 h at room temperature. The resulting yellow solution was poured into a beaker containing water (10 mL) and left overnight for complete oxidation and hydrolysis. The reaction mixture was extracted several times with dichloromethane and the combined organic phases were dried over anhydrous MgSO4. Evaporation of the solvent gave the title compound as a brown oil which was subsequently purified by column chromatography on silicagel, by using n-hexane as eluent. Yield: 0.84 g, 57%. 1H NMR (CDCl3, 400 MHz): d = 7.28–7.33 (m, 2H, H3,5), 7.22–7.25 (m, 1H, H4), 3.50 (s, 4H, H7,70 ), 2.46 (br., 16H, H8-11,80 -110 ), 2.27 (s, 6H, NCH3). 13C NMR (CDCl3, 100 MHz): d = 138.27 (C1), 129.29 (C3,5), 128.29 (C2,6), 127.11 (C4), 63.15 (C7,70 ), 55.21 (C8,11,80 ,110 ), 53.16 (C9,10,90 ,100 ), 46.15 (NCH3). 77Se NMR (CDCl3, 76 MHz): d = 424.8. HRMS (ESI+), m/z (%): 381.1550 (100), [{2,6-MeN(CH2CH2)2NCH2}2C6H3Se+], calcd. for C18H29N4Se: m/z = 381.1552.
2. Experimental 2.1. Materials and methods Starting materials were commercially available and used without further purification (SO2Cl2, 2-bromo-1,3-dimethylbenzene, Nmethylpiperazine, morpholine and nBuLi) or were prepared according to literature procedures: 1-Br-2,6-[MeN(CH2CH2)2NCH2]2C6H3 [21], 1-Br-2,6-[O(CH2CH2)2NCH2]2C6H3 [22], [2,6(Me2NCH2)2C6H3]SeCl [15], [AuC6F5(tht)] and [AuCl(tht)] [23]. Organic solvents were dried and distilled under argon by following standard procedures prior to use. Experiments involving air sensitive compounds were performed under argon atmosphere. Elemental analyses were made on a Flash EA 1112 analyzer. Melting points were measured on an Electrothermal 9200 apparatus. 1H, 13 C, 19F and 77Se NMR spectra were recorded in CDCl3 at room temperature on a Bruker 400 or 600 MHz spectrometer. The chemical shifts are reported in d units (ppm) relative to TMS (1H and 13C), CFCl3 (19F) and Me2Se (77Se). The NMR data were processed using the MestReNova software [24]. The assignments of the 1H and 13 C chemical shifts are based on 2D NMR correlation experiments (COSY, HSQC and HMBC) and are given according to the numbering depicted in Scheme 1. ESI mass spectra were recorded using a Thermo Scientific LTQOrbitrapXL instrument equipped with a standard ESI/APCI source.
2.2.2. [2,6-{O(CH2CH2)2NCH2}2C6H3]2Se2 (2) [2,6-{O(CH2CH2)2NCH2}2C6H3]2Se2 (2) was obtained similarly with 1, as a brown oil, from nBuLi in hexane (1.98 mL, 1.6 M, 3.18 mmol), 1-Br-2,6-[O(CH2CH2)2NCH2]2C6H3 (1.13 g, 3.18 mmol) and selenium powder (0.25 g, 3.18 mmol). Yield: 0.83 g, 73%. 1H NMR (CDCl3, 400 MHz): d = 7.35–7.38 (m, 2H, H3,5), 7.22–7.25 (m, 1H, H4), 3.69–3.72 (m, 8H, H8,11,80 ,110 ), 3.50 (s, 4H, H7,70 ), 2.45 (br, 8H, H9,10,90 ,100 ). 13C NMR (CDCl3, 100 MHz): d = 137.85 (C1), 129.31 (C3,5), 128.36 (C2,6), 127.25 (C4), 67.09 (C8,11,80 ,110 ), 63.57 (C7,70 ), 53.72 (C9,10,90 ,100 ). 77Se NMR (CDCl3, 76 MHz): d = 400.1. HRMS (ESI+ ), m/z (%): 355.0913 (100) [2,6-{O(CH2CH2)2NCH2}2C6H3Se+], calcd. for C16H23N2O2Se: m/z = 355.0919. 2.2.3. Synthesis of [2,6-{MeN(CH2CH2)2NCH2}2C6H3Se]+Cl (3) A solution of sulfuryl chloride (0.483 g, 3.6 mmol) in toluene (20 mL) was added dropwise to a solution of [2,6-{MeN(CH2CH2)2NCH2}2C6H3]2Se2 (1) (2.75 g, 3.6 mmol) in toluene (10 mL) under stirring. The reaction mixture was stirred over night at room temperature. The resulting solid was filtered off and solubilized in dichloromethane. The obtained solution was washed with a NaOH 5 M aqueous solution (20 mL), separated and dried over Na2SO4. After removing the solvent, a pale yellow solid was obtained. Yield: 2.00 g, 66%. M.p. 192 °C. Anal. Calc. for C18H29ClN4Se (MW = 415.86): C, 51.99; H, 7.03; N, 13.47. Found: C, 51.63; H
Scheme 1. Numbering scheme for NMR assignments in compounds 1–8.
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6.95; N, 13.54%. 1H NMR (CDCl3, 600 MHz): d = 7.20–7.34 (m, 6H, H3-5), 3.52 (s, 4H, H7,70 ), 2.56 (br, 16H, H8-11,80 -110 ), 2.36 (s, 6H, NCH3). 13C NMR (CDCl3, 150 MHz): d = 137.71 (C1), 129.16 (C2,6), 128.24 (C3,5), 127.16 (C4), 62.71 (C7,70 ), 54.78 (C9,10,90 ,100 ), 52.21 (C8,11,80 ,110 ), 45.47 (NCH3). 77Se NMR (CDCl3, 57.24 MHz): d = 1198. ESI+ MS, m/z (%): 381.15 (100), [2,6-{MeN (CH2CH2)2NCH2}2C6H3Se+]. 2.2.4. [2,6-{O(CH2CH2)2NCH2}2C6H3Se]+Cl (4) Similarly with 3, as a pale yellow solid, from [2,6-{O(CH2CH2)2NCH2}2C6H3]2Se2 (2) (1.19 g, 1.68 mmol) and sulfuryl chloride (0.227 g, 1.68 mmol). Yield: 0.70 g (53.4 %). M.p. 185 °C. Anal. Calc. for C16H23N2O2SeCl (MW = 389.78): C, 49.30; H, 5.95; N, 7.19. Found: C, 49.72; H, 6.18; N, 7.12%. 1H NMR (CDCl3, 600 MHz): d = 7.62–7.64 (m, 1H, H4), 7.40–7.42 (m, 2H, H3,5), 4.25 (AB spin system with dA 4.24 and dB 4.26, 2JHH 5.23 Hz, 4H, H7,70 ), 4.21 (dt, 2 JHpro-cis,Hpro-trans 13.2, 3JHpro-cis,Hpro-trans 2.9 Hz, 4H, pro-cisH9,90 ,10,100 ), 3.89 (dd, 2JHpro-cis,Hpro-trans 13.0, 3JHpro-cis,Hpro-trans 3.5 Hz, 4H, pro-trans-H9,90 ,10,100 ), 3.34 (d, 2JHpro-cis,Hpro-trans 12.1 Hz, 4H, procis-H8,80 ,11,110 ), 2.92 (dt, 2JHpro-cis,Hpro-trans 12.4, 3JHpro-cis,Hpro-trans 3.7 Hz, 4H, pro-trans-H8,80 ,11,110 ). 13C NMR (CDCl3, 150 MHz): d = 131.68 (C4), 130.37 (C2,6), 129.42 (C3,5), 127.53 (C1), 63.63 (C8,80 ,11,110 ), 61.18 (C7,70 ), 51.39 (C9,90 10,100 ). 77Se NMR (CDCl3, 57.24 MHz): d = 655. ESI+ MS, m/z (%): 355.10 (100) [2,6-{O (CH2CH2)2NCH2}2C6H3Se+]. 2.2.5. Synthesis of [2,6-{MeN(CH2CH2)2NCH2}2C6H3Se]+[AuCl2] (5) AuCl(tht) (0.074 g, 0.23 mmol) was added to a solution of 2,6[MeN(CH2CH2)2NCH2]2C6H3SeCl (3) (0.097 g, 0.23 mmol) in dichloromethane (15 mL), at room temperature, under stirring. After 2 h the solvent was removed in vacuum and the resulting pale yellow precipitate was washed with Et2O. Yield: 0.098 g (65%), M.p. 216 °C. Anal. Calc. for C18H29AuCl2N4Se (MW = 648.28): C, 33.35; H, 4.51; N, 8.64. Found: C, 33.74; H, 4.61; N, 8.72%; 1H NMR (CDCl3, 600 MHz): d = 7.25–7.37 (m, 3H, H3-5), 3.68 (s, 4H, H7,70 ), 3.35–3.56 (br., 8H, H8,11,80 ,110 ), 2.91 (br., 8H, H9,90 ,10,100 ), 2.84 (s, 6H, CH3). 13C NMR (CDCl3, 150 MHz): d = 135.42 (C1), 129.50 (C2,6), 128.79 (C3,5), 128.29 (C4), 61.82 (C7,70 ), 49.63 (C8,11,80 ,110 ), 44.05 (NCH3), 40.32 (C9,90 ,10,100 ). The 77Se resonance could not be detected. ESI+ MS, m/z (%): 381.15 (100), [2,6-{MeN(CH2CH2)2NCH2}2C6H3Se+]. ESI- MS m/z (%): 266.91 (100) [AuCl 2 ]. 2.2.6. [2,6-{O(CH2CH2)2NCH2}2C6H3Se]+[AuCl2] (6) Similarly with 5, from AuCl(tht) (0.083 g, 0.25 mmol) and 2,6-[O (CH2CH2)2NCH2]2C6H3SeCl (4) (0.100 g, 0.25 mmol), as a pale yellow solid. Yield: 0.125 g (78.6%), M.p. 81 °C. Anal. Calc. for C16H23AuCl2N2O2Se (MW = 622.20): C, 30.89; H, 3.73; N 4.50. Found: C, 30.74; H, 3.56; N, 4.42%. 1H NMR (CDCl3, 600 MHz): d = 7.62–7.66 (m, 1H, C6H3), 7.38–7.43 (m, 2H, C6H3), 4.27 (s, 4H, H7,70 ), 4.17 (t, 2 JHH = 12.2 Hz, 4H, pro-trans-H8,11,80 ,110 ), 3.91 (d, 2JHH = 12.9 Hz, 4H, pro-cis-H8,11,80 ,110 ), 3.35 (d, 2JHH = 12.2 Hz, 4H, pro-trans-H9,10,90 ,100 ), 2.97 (t, 2JHH = 10.2 Hz, 4H, pro-cis-H9,10,90 ,100 ). 13C NMR (CDCl3, 150 MHz): d = 131.70 (C2,6), 130.39 (C4), 129.43 (C3,5), 127.50 (C1), 63.65 (C8,11,80 ,110 ), 61.23 (C7,70 ), 51.49 (C9,10,90 ,100 ). The 77Se resonance could not be detected. ESI+ MS m/z (%): 355.09 (42) [2,6-{O(CH2CH2)2NCH2}2C6H3Se+], 268.02 (100) [{2,6-O(CH2CH2)2NCH2}2C6H3Se+ O(CH2CH2)2N]. ESI– MS, m/z (%): 266.91 (100) [AuCl 2 ]. 2.2.7. [2,6-(Me2NCH2)2C6H3Se]+[AuCl2] (7) Similarly with 5, from AuCl(tht) (0.084 g, 0.26 mmol) and [2,6(Me2NCH2)2C6H3]SeCl (0.081 g, 0.26 mmol), in CHCl3 (20 mL), as an orange solid. Yield: 0.121 g, 86 %, M.p. 136 °C. Anal. Calc. for C12H19AuCl2N2Se (MW = 538.13): C, 26.78; H, 3.56; N, 5.21. Found: C, 26.81; H, 3.72; N, 5.28%. 1H NMR (CDCl3, 600 MHz): d = 7.27– 7.30 (m, 3H, H3-5), 4.11 (s, 4H, H7,70 ), 2.96 (s, 12H, NCH3). 13C
281
NMR (CDCl3, 150 MHz): d = 132.88 (C1), 132.25 (C2,6), 128.55 (C4), 126.02 (C3,5), 64.28 (C7,70 ), 49.14 (NCH3). The 77Se resonance was not observed. ESI+ MS, m/z (%): 271.07 (100) [2,6-(Me2NCH2)2C6H3Se+]; ESI- MS, m/z (%): 266.90 (100) [AuCl 2 ], 503.01 (74) [2,6(Me2NCH2)2C6H3SeAuCl]. 2.2.8. Synthesis of [2,6-(Me2NCH2)2C6H3Se]+[Au(C6F5)2] (8) (C6F5)Au(tht) (0.150 g, 0.33 mmol) was added to a solution of [2,6-(Me2NCH2)2C6H3]2Se2 (0.087 g, 0.16 mmol) in dichloromethane (15 mL), at room temperature, under stirring. After 30 minutes a black precipitate was formed and it was filtered off. From the clear solution the solvent was removed at reduced pressure and the remained yellow solid was washed with cold hexane. Yield: 0.08 g, 60%, M.p. 136 °C. Anal. Calc. for C24H19AuF10N2Se (MW = 801.33): C, 35.97; H, 2.39; N, 3.50. Found: C, 35.71; H, 2.48; N, 3.27%. 1H NMR (CDCl3, 400 MHz): d = 7.28 (t, 3JHH 7.5 Hz, 1H, H4), 7.18 (d, 3JHH 7.4 Hz, 2H, H3,5), 4.00 (s, 4H, H7,70 ), 2.87 (s, 12H, NCH3). 13C NMR (CDCl3, 100 MHz): d = 149.00 (ddm, 1JFC 223.8 Hz, 2JFC 26.7 Hz, C6F5-ortho). 143.56 (C1), 137.62 (dm, 1JFC 246.3 Hz, C6F5-para), 137.16 (dm, 1JFC 250.2 Hz, C6F5-meta), 132.06 (C2,6), 128.29 (C4), 126.03 (C3,5), 64.35 (C7,70 ), 49.10 (NCH3). The 13C resonance for C6F5-ipso could not be unambigu19 ously assigned. F NMR (CDCl3, 376 MHz): d = 114.87 115.02 (m, 4F, AuC6F5-ortho), 161.59 (t, 2F, 3JFF 21.12 Hz, AuC6F5-para), 163.20 163.41 (m, 4F, AuC6F5-meta). 77 Se NMR (CDCl3, 76 MHz): d = 1208. ESI+ MS, m/z (%): 271.07 (100) [2,6-(Me2NCH2)2C6H3Se+]; ESI- MS, m/z (%): 530.94 (100) [Au(C6F5) 2 ]. 2.3. Crystal structure determination Single crystals of 4H2O were obtained from methylene dichloride/n-hexane (1:3, by volume) and those of 7 and 8 from a mixture of acetone and Et2O (1:3, by volume). The details of the crystal structure determination and refinement are given in the Supplementary Information (SI), Table S1. Data were collected on a Bruker SMART APEX diffractometer, by using graphitemonochromated Mo Ka radiation (k = 0.71073 Å). The crystals were attached on cryoloops to a glass fiber and data were collected at room temperature (297 K). The structures were refined with anisotropic thermal parameters. The hydrogen atoms H17 and H18 of the water molecule in 4H2O were located in a difference Fourier map and they were freely refined. All the other hydrogen atoms were refined with a riding model and a mutual isotropic thermal parameter. For structure solving and refinement the software package SHELXL-2014 was used [25]. The drawings were created with the Diamond program [26]. Intermolecular contacts were found in PLATON [27]. 3. Results and discussion 3.1. Synthesis The diorganodiselenides [2,6-{E(CH2CH2)2NCH2}2C6H3]2Se2 [E = MeN (1), O (2)] were prepared by a succession of reactions, involving lithiation of the corresponding 1-Br-2,6-{E(CH2CH2)2NCH2}2C6H3, selenium insertion into the new formed carbon– lithium bond, oxidation and hydrolysis of the lithium organoselenolate, as depicted in Scheme 2, similarly with the procedure reported previously for the diorganodiselenide [2,6-(Me2NCH2)2C6H3]2Se2 [15]. Further oxidation of the diorganodiselenides 1 and 2 with SO2Cl2 resulted in the corresponding organoselenium chlorides 3 and 4, respectively. These were subsequently used in reactions with [AuCl(tht)], when the ionic organoselenium dichloroaurates 5 and 6 were obtained in moderate yields, as pale
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Scheme 2. Synthesis of compounds 1–8.
yellow solids. Similarly, the reaction between [2,6-(Me2NCH2)2C6H3Se]+Cl and [AuCl(tht)] resulted in [2,6-(Me2NCH2)2C6H3Se]+ [AuCl2] (7), while [2,6-(Me2NCH2)2C6H3Se]+[Au(C6F5)2] (8) was obtained by reacting the diorganodiselenide [2,6-(Me2NCH2)2C6H3]2Se2 with [(C6F5)Au(tht)] in a 1:2 molar ratio. We observed previously that the diorganodiselenide with one pendant arm [2(Me2NCH2)2C6H4]2Se2 give a ligand exchange reaction with [Sn{N (SiMe3)2}2], while Ph2Se2 oxidizes Sn(II) to Sn(IV) in the reaction with Sn(II) bis amide [28]. The formulation of all new compounds is supported by elemental analysis, mass spectrometry and NMR spectroscopy (1H, 13C, 19F and 77Se). 3.2. Spectroscopic characterization The room temperature NMR spectra of the diorganodiselenides 1 and 2, as well as the organoselenium chlorides 3 and 4 are consistent with the presence of only one species in solution, with equivalent pendant arms attached to the C6H3 rings. In these species, except compound 4, the 1H NMR resonance for the equivalent H7 and H70 protons (CH2N, for numbering see Scheme 1) appears as one sharp singlet. The methylene protons in the methylpiperazinyl group, both in 1 and 3, give rise to a broad 1H NMR resonance, while the methyl groups are sharp singlets (see SI, Fig. S1). The broad resonance corresponding to the methylene MeN(CH2CH2)2 protons suggest close d values for the non-equivalent protons H8,11/H80 ,110 and H9,10/H90 ,100 respectively, in the two pendant arms, as well as a fast conformation inversion of the piperazinyl six membered ring, resulting in the equivalence of the protons in equatorial and axial positions. Moreover, the 1H NMR spectra for compounds 1 and 3 suggest either the absence of any N?Se intramolecular coordination or a very fast dynamic behaviour in solution, involving decoordination of nitrogen, rotation around the C7/70 –N bonds, pyramidal inversion at nitrogen, recoordination and conformation inversion of the sixmembered rings (see SI, Fig. S2). A similar behaviour was previously observed for the proligand 1,3-[MeN(CH2CH2)2NCH2]2C6H4 [29]. The non-equivalent H8,11/H80 ,110 and H9,10/H90 ,100 protons in 2
give two multiplet resonances (see SI, Fig. S3), similarly with the situation found in the 1H NMR spectra of 1,3-[O(CH2CH2)2NCH2]2C6H4 [30], or the related one pendant arm species [2-{O(CH2CH2)2NCH2}C6H4]2Se2 [11]. This behaviour suggests, again, either the absence of any N?Se intramolecular interaction or a very weak N?Se interaction which allows the dynamic behaviour described above for compounds 1 and 3. By contrast, the methylene protons in the six membered morpholinyl rings of 4 show four distinct multiplet resonances (see SI, Fig. S3), assigned to the non-equivalent pro-cis (Ha and Hc in Scheme 1) and respectively pro-trans (Hb and Hd in Scheme 1) protons, designated like this by considering the position of the Se atom in relation with the morpholinyl rings. In this case the conformation change of the six-membered rings is much slower and the resonances of the non-equivalent equatorial and axial protons, respectively, are observable at the NMR time scale. Such a behaviour of compound 4 is possible only if the intramolecular N?Se coordination of both arms is preserved in solution at room temperature and any fast dynamic behaviour (see SI, Fig. S2) is absent. The 1H NMR spectra of compounds 5 and 6 suggest the equivalence of the two pendant arms in solution as well. By contrast with the chloride 3, the cation in 5 presents two multiplet resonances for the non-equivalent H8,11/H80 ,110 and H9,10/H90 ,100 protons, while in case of compound 6 a similar pattern as for compound 4, showing four different resonances for the nonequivalent pro-cis and pro-trans H8,11/H80 ,110 and H9,10/H90 ,100 protons was observed, thus confirming the existence of the N?Se interactions in solution at room temperature at least for compound 6, while in case of compound 5 we assume very labile N?Se interactions. For compounds 7 and 8 the singlet resonances corresponding to the H7 and the N(CH3)2 protons indicate either no intramolecular N?Se interaction or a very weak one, which determines a fluxional behaviour at room temperature. The 77Se{H} NMR resonances of 1 and 2 are located around 400 ppm, as expected for diorganodiselenides, while the 77Se{H} NMR resonances of the organoselenium chlorides are strongly low field shifted (d = 1198 ppm for 3 and 655 ppm for 4). The 77 Se NMR resonance could not be observed for compounds 5–7,
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but for compound 8 it is located at 1208 ppm, thus confirming the ionic nature of this species in solution. The 19F NMR spectrum of compound 8 shows the expected multiplet resonances for the ortho, meta and para fluorine atoms in the two C6F5 equivalent groups. The 13C{H} NMR spectra show the expected singlet resonances in the aliphatic and the aromatic regions for the organic groups attached to selenium. The 13C NMR resonances given by the C6F5 groups appear as doublets of multiplets due to the 19F–13C couplings, with large 1JFC coupling constants (range 223–249 Hz), similarly with the 13C NMR spectrum of the starting [(C6F5)Au(tht)] (see SI, Fig. S4). The ESI+ mass spectra show in all cases the organoselenium cation, [2,6-{E(CH2CH2)2NCH2}2C6H3Se+] or [2,6-(Me2NCH2)2C6H3Se+] as base peak. For the gold complexes the ESI- mass spectra show the [AuCl 2 ] and the [Au(C6F5)2 ] anions at m/z = 266.90 and 530.94, respectively, as base peaks. 3.3. Single-crystal X-ray diffraction studies
Fig. 2. Thermal ellipsoids representation at 30% probability for RN1,RN10 -7. Hydrogen atoms are omitted for clarity.
The molecular structures of 4H2O, 7 and 8, with the corresponding atom numbering schemes, are shown in Figs. 1–3, respectively, and selected interatomic distances and angles are listed in Table 1. All three compounds are ionic species, containing the cation [2,6-{O(CH2CH2)2NCH2}2C6H3Se]+ in 4H2O and [2,6(Me2NCH2)2C6H3Se]+ in 7 and 8, respectively. The three structures display several common features: – in each cation, both nitrogen atoms in the pendant arms are intramolecularly coordinated to selenium, thus resulting in 10-Se-3 species [31] with a distorted T-shaped (N,C,N)Se core with N–Se–N angles of 161.58(7)° in 4H2O, 161.8(3)° in 7, and 161.9(2)° in 8, respectively. The strong N?Se intramolecular interactions [2.2489(19)/2.1706(19) Å in 4H2O, 2.174(5) Å in 7 and 2.171(4)/2.179(6) Å in 8] are close to those found in the ionic species [{2,6-(Me2NCH2)2C6H3}Se]+ClH2O [2.183(2) and 2.184(2) Å] [15], [{2,6-(Me2NCH2)2C6H3}Se]+BrH2O [2.181(3) and 2.185(3) Å] [32] or [{2,6-(Me2NCH2)2C6H3}Se]+[Ph2SbCl4] [2.178(3) and 2.160(3) Å] [15] and well below the sum of the van der Waals radii of the two elements [RrvdW(N, Se) 3.54 Å] [33]. The difference between the two N?Se distances in 4H2O might be explained by a slightly unbalanced 3c–4e N?Se(C)–N system with the nitrogen atom of one pendant arm acting as a donor towards the Se–N acceptor moiety which include the nitrogen atom of the other arm of the pincer
Fig. 3. Thermal ellipsoids representation at 30% probability for RN1,RN2-8. Hydrogen atoms are omitted for clarity.
Table 1 Selected interatomic distances (Å) and angles (deg.) in compounds 4H2O, 7a and 8.
C(1)–Se(1) N(1)–Se(1) N(2)/N(10 )–Se(1) Au(1)–Cl(1)/Cl(10 ) N(1)–Se(1)–N(2)/N(10 ) C(1)–Se(1)–N(1) C(1)–Se(1)–N(2)/N(10 ) Cl(1)–Au(1)–Cl(10 ) C(13)–Au(1)–C(19) a
Fig. 1. Thermal ellipsoids representation at 30% probability for RN1,SN2-4H2O. Water molecule and hydrogen atoms are omitted for clarity.
4H2O
7
8
1.894(2) 2.2489(19) 2.1706(19)
1.866(9) 2.174(5) 2.174(5) 2.236(3) 161.8(3) 80.89(15) 80.89(16) 178.3(2)
1.889(9) 2.171(4) 2.179(6)
161.58(7) 80.08(9) 81.51(9)
161.9(2) 80.80(3) 81.12(3) 178.09(3)
Symmetry equivalent atoms (1 x, y, 0.5 z) in 7 are given by ‘‘prime”.
ligand, as we observed both at experimental and theoretical level (DFT calculations) for the related species [{2,6-(Me2NCH2)2C6H3}Se]+X (X = Cl, Br, I) [15]; – the two five-membered rings formed in each cation by the intramolecular N?Se coordination are not planar, but folded about an imaginary carbon-selenium axis, with the nitrogen atoms out of the residual C3Se plane: N1/N2 at 0.55/0.58 Å above and below the C1C2C7Se1 and C1C6C12Se1 planes, respectively, in 4H2O, N1/N10 at 0.55 Å above the C1C2C5Se1/ C1C20 C50 Se1 planes in 7 and N1/N2 at 0.56/0.54 Å above and below the C1C2C7Se1 and C1C6C12Se1 planes, respectively, in 8.
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Fig. 6. Cation–anion association in the crystal of 8. F18 H7B0 2.48 Å. Symmetry equivalent position x, 1 + y, 1 + z is given by ‘‘prime”. Hydrogen atoms not involved in F H interactions are omitted for clarity.
Fig. 4. Dimeric association in 4H2O. H8B Cg0 2.95 Å. (symmetry equivalent position x, 1 y, z is given by ‘‘prime”). Hydrogen atoms not involved in intermolecular interactions are omitted for clarity.
– as a consequence of the intramolecular coordination, the two five-membered rings in each cation display planar chirality (with the aromatic ring as chiral plane and the nitrogen atom as pilot atom) [34]. The crystals of the three compounds contain racemic mixtures of RN1,SN2 and SN1,RN2 isomers in 4H2O, RN1, RN2 and SN1,SN2 isomers in 8, and RN1,RN10 and SN1,SN10 isomers in 7. The morpholinyl rings in 4H2O have a chair conformation, with the nitrogen and the oxygen atoms in apices. In the crystal of 4H2O the cations are associated in dimeric units (Fig. 4) by p C– H Arylcentroid contacts, shorter than 3.1 Å, between the C6H3 ring and a hydrogen atom in the morpholinyl group of a neighbouring cation, with a c angle between the normal to the aromatic ring and the line defined by the H atom and the Arcentroid smaller than 30° [35], namely CH8B Cg(C1–C6) 2.95 Å, c 13.24°. In the crystal lattice the Cl anions interact with the water molecules by hydrogen bonding (Cl1 H17 2.51 Å, Cl1 H18 2.64 Å vs. RrvdW(Cl,H) 3.01 Å [33]), thus giving rise to infinit polymeric chains to which are interconnected the dimeric cations by hydrogen bonding as well (H2O H3 2.46 Å vs. RrvdW(O,H) 2.60 Å [33], see SI, Fig. S5). The so formed layers are further connected in a 3D supramolecular network by additional Cl H interactions (Cl1 H12B 2.76 Å, see SI, Fig. S6). In compound 7 weak Cl H contacts are established between the [AuCl2] anions and the organoselenium cations. Each chlorine atom in the anions participate in three such contacts, involving
hydrogen atoms in the pendant arms of the cations. Polymeric chains are formed with the participation of the same chlorine atom in the anion and hydrogens of the pendant arms of the neighbouring cations (Cl1 H5B 2.79 Å and Cl1 H7B 2.83 Å), as depicted in Fig. 5. The third Cl H contact (Cl1 H6C 2.94 Å) is established between the as formed chains, thus leading to a layered 2D network (see SI, Fig. S7). No further contacts between these layers are present. The crystal of 8 has a layered structure as well, built by weak F H contacts established between the [Au(C6F5)2] anions and the organoselenium cations. Each anion participates with four fluorine atoms in such interactions, three of them belonging to the same C6F5 group, and the fourth to the other one. A cation–anion unit showing the F H interactions involved in the construction of the extended 2D network is depicted in Fig. 6. The three fluorine atoms in the same C6F5 group (F16 H11C 2.61 Å, F17 H10B 2.59 Å and F18 H7B 2.48 Å, vs. RrvdW(H,F) 2.67 Å [33]) interact with hydrogen atoms in the two pendant arms of the cations, while the fluorine atom in the other C6F5 group of the anion (F23 H4 2.62 Å) interact with the C6H3-para hydrogen atom (see SI, Fig. S8). 4. Conclusions In solution, for all compounds was observed the equivalence of the two pendant arms in the pincer N,C,N ligand. The 1H NMR spectra provided evidences that the N?Se intramolecular coordination observed in solid state is preserved in solution at room temperature as well only for compound 4, for which four distinct multiplet resonances, assigned to the non-equivalent pro-cis and respectively pro-trans protons in the morpholinyl ring were noticed. For the methylpiperazinyl substituted aryl groups in compounds 1, 3 and
Fig. 5. Polymeric chain in compound 7. Cl1a H7B 2.83 Å, Cl1a H5Bb 2.79 Å. Symmetry equivalent positions 0.5 x, 0.5 y, 1 z and x, 1 y, 1 z are given by ‘‘a” and ‘‘b”, respectively. Hydrogen atoms not involved in Cl H interactions are omitted for clarity.
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5 the broad resonances in the aliphatic region suggest a fast conformation change of the MeN(CH2CH2)2N moiety. Except compound 4, for which an AB spin system was observed, the resonance corresponding to the H7,70 protons in the CH2N moiety appears as a sharp singlet, due to a dynamic process involving decoordination, inversion at nitrogen and recoordination to selenium, too fast to be observed at room temperature. The cations [2,6-{O(CH2CH2)2NCH2}2C6H3Se]+ in 4H2O and [2,6(Me2NCH2)2C6H3Se]+ in 7 and 8 exhibit in solid state a T-shaped CSeN2 core (10–Se–3 hypercoordinated species) and we assume for all the other ionic compounds described in this paper a similar behaviour in solid state. Funding information Financial support from the National University Research Council of Romania (Research Project PNII-ID 0659/2011) is greatly appreciated. A. Pop is grateful for the financial support from Babeș-Bolyai University, Romania (Research project GTC31809/23.03.2016).
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Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.poly.2018.12.041.
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