Tetrabromoethane As -Hole Donor Toward Bromide Ligands: Halogen
Total Page：16
File Type：pdf, Size：1020Kb
crystals Article Tetrabromoethane as s-Hole Donor toward Bromide Ligands: Halogen Bonding between C2H2Br4 and Bromide Dialkylcyanamide Platinum(II) Complexes Anna M. Cheranyova and Daniil M. Ivanov * Institute of Chemistry, Saint Petersburg State University, 199034 Saint Petersburg, Russia; [email protected] * Correspondence: [email protected] Abstract: The complexes trans-[PtBr2(NCNR2)2] (R2 = Me2 1, (CH2)5 2) were cocrystallized with 1,1,2,2-tetrabromoethane (tbe) in CH2Cl2 forming solvates 1·tbe and 2·tbe, respectively. In both solvates, tbe involved halogen bonding, viz. the C–Br···Br–Pt interactions, were detected by single- crystal X-ray diffractions experiments. Appropriate density functional theory calculations (M06/def2- TZVP) performed for isolated molecules and complex-tbe clusters, where the existence of the inter- actions and their noncovalent nature were confirmed by electrostatic potential surfaces (r = 0.001 a.u.) for isolated molecules, topology analysis of electron density, electron localization function and HOMO-LUMO overlap projections for clusters. Keywords: tetrabromoethane; halogen bonding; platinum(II); dialkylcyanamides Citation: Cheranyova, A.M.; Ivanov, D.M. Tetrabromoethane as s-Hole 1. Introduction Donor toward Bromide Ligands: In the past decade, the halogen bonding (XB) concept [1] has attracted a considerable Halogen Bonding between C2H2Br4 attention as a new type of intermolecular interaction and has now become an important and Bromide Dialkylcyanamide tool for XB involving crystal engineering. The expressed directionality of XB was subse- Platinum(II) Complexes. Crystals quently used in biology and materials sciences to create functional systems with a wide 2021, 11, 835. https://doi.org/ range of applications spanning from supramolecular chemistry, to crystal engineering, 10.3390/cryst11070835 catalysis, electrochemistry, etc. [2–6]. Although the vast majority of XB studies do not utilize organometallic building blocks, these metal-containing species functioning as XB Academic Editor: Sergiy Rosokha participants are very useful for the design of new supramolecular systems [7–10]. Involvement of various haloalkanes (in particular bromoalkanes) in the occurrence Received: 4 July 2021 of XBs is among rapidly growing areas of XB based crystal engineering [3]. Perfluo- Accepted: 17 July 2021 Published: 20 July 2021 rinated bromoalkanes were found [11–13] to form XBs with metal-free halide anions. Dibromomethane [14,15], bromoform [16,17], tetrabromomethane [16,18,19] and hexabro- Publisher’s Note: MDPI stays neutral moethane [20], functioning as XB acceptors, were studied toward halide ligands in metal with regard to jurisdictional claims in complexes. published maps and institutional affil- 1,1,2,2-tetrabromoethane (tbe), which contains the same CHBr2 fragments as those iations. in dibromomethane or bromoform, have never been utilized as XB donor (Figure1). This compound is used in organic chemistry as an alkylating agent [21,22] and in ferrocene chemistry as a mild brominating agent [23–27]. The only tbe solvates were obtained [28], but they were only characterized by elemental analyses. In this study, the dialkylcyanamide platinum(II) complexes trans-[PtBr (NCNR ) ] Copyright: © 2021 by the authors. 2 2 2 1 2 Licensee MDPI, Basel, Switzerland. (R2 = Me2 , (CH2)5 ), which function as useful XB acceptors [18,29], were employed This article is an open access article as XB acceptors toward tbe (Figure1). Since tbe may be a source of bromides, the bro- distributed under the terms and mide complexes were chosen in order to exclude various exchange reactions between the conditions of the Creative Commons halogens. Attribution (CC BY) license (https:// We report herein our data on cocrystallization of tbe with dialkylcyanamide bromide creativecommons.org/licenses/by/ complexes of platinum (II). In 1:1 solvates 1·tbe and 2·tbe, the first examples of tbe involved 4.0/). XBs and hydrogen bonds (HBs) were found. Crystals 2021, 11, 835. https://doi.org/10.3390/cryst11070835 https://www.mdpi.com/journal/crystals Crystals 2021, 11, x FOR PEER REVIEW 2 of 11 Crystals 2021, 11, 835 2 of 10 FigureFigure 1. Studied 1. Studied XB partners. XB partners. 2. Materials and Methods We report herein our data on cocrystallization of tbe with dialkylcyanamide bromide 1,1,2,2-C2H2Br4,K2[PtCl4], KBr, dialkylcyanamides and all solvents were obtained fromcomplexes commercial of sources platinum and used (II). as In received; 1:1 solvates complex 1trans·tbe-[PtBr and2 (NCNMe2·tbe, the2)2]( first1) was examples of tbe synthesizedinvolved viaXBs a previouslyand hydrogen published bonds procedure (HBs) [ 29were]. found. 2.1. Synthesis of Complex Trans-[PtBr2(NCN(CH2)5)2] 2. Materials and Methods To K2[PtCl4] (0.1 g, 0.24 mmol) in water (1 mL) added a 10-fold excess of KBr (0.284 g, ◦ 2.4 mmol),1,1,2,2-C whereupon2H2Br the4, solutionK2[PtCl was4], KBr, heated dialkylcyanamides with mixing for 2 h at 70andC. Afterall solvents heating were obtained thefrom solution commercial became maroon. sources A and 5-fold used excess as ofreceived; NCNC5H complex10 (0.140 mL, trans 1.2-[PtBr mmol)2(NCNMe was 2)2] (1) was addedsynthesized to this solution. via a previously Oil formed at published the bottom ofprocedure the vessel after[29]. 24 h. The resulting oil was powdered with diethyl ether and held under ultrasound. The resulting precipitate (a mixture of cis- and trans-isomers) was washed with three portions of 3 mL of water and diethyl2.1. Synthesis ether, and of then Complex dried in Trans-[PtBr air at room temperature.2(NCN(CH2 To)5) isolate2] the pure trans-isomer, the resulting mixture was dissolved in CHCl and was refluxed for 3 h. Yield: 71%. 1H To K2[PtCl4] (0.1 g, 0.24 mmol) in3 water (1 mL) added a 10-fold excess of KBr (0.284 NMR (400 MHz, CDCl3) δ = 3.32 (m, NCH2), 1.62–1.67 (m, NCH2CH2) and 1.52–1.59 (m, g, 2.4 mmol), whereupon the13 solution1 was heated with mixing for 2 h at 70 °C. After NCH2CH2CH2) ppm (Figure S5). C{ H} NMR (101 MHz, CDCl3) δ = 115.74 (s, C≡N), 5 10 49.79heating (s, NC theH2CH2), solution 24.53 became (s, CH2C Hma2CHroon.2) and A 22.485-fold (s, CHexcess2CH 2ofCH NCNC2) ppm (FigureH (0.140 S6). mL, 1.2 mmol) 195 wasPt NMR added (86 MHz,to this CDCl solution.3) δ = − Oil2596.15 formed ppm (Figureat the bottom S7). HRESI-MS, of the vessel m/z: calculated after 24 h. The resulting foroil [M+H] was +powdered576.9732, found with 576.9755 diethyl (Figure ether S4).and Single held crystalsunder ofultrasound.2 were prepared The fromresulting precipitate a(a dichloromethane mixture of cis- at and RT by trans slow-isomers) evaporation was (Figure washed S1). Comparisonwith three ofportions the XRD of and 3 mL of water and PXRD data showed that the phases coincide (Figure S8). diethyl ether, and then dried in air at room temperature. To isolate the pure trans-isomer, 2.2.the Crystallization resulting mixture was dissolved in CHCl3 and was refluxed for 3 h. Yield: 71%. 1H NMRSingle (400 crystals MHz, of 1 ·tbeCDCland32) ·δtbe =were 3.32 obtained (m, NC byH slow2), 1.62–1.67 evaporation (m, of a dichloromethaneNCH2CH2) and 1.52–1.59 (m, solution (1 mL) of a mixture of the corresponding 1 (0.002 mmol) or 2 (0.002 mmol) and tbe NCH2CH2CH2) ppm (Figure S5). 13C{1H} NMR (101 MHz, CDCl3) δ = 115.74 (s, C≡N), 49.79 2 1·tbe 2·tbe taken in an excess (0.87 mmol) at RT. Yellow crystals , and of suitable for XRD 195 were(s, releasedNCH2CH2), after 3− 24.534 d. (s, CH2CH2CH2) and 22.48 (s, CH2CH2CH2) ppm (Figure S6). Pt NMR (86 MHz, CDCl3) δ = −2596.15 ppm (Figure S7). HRESI-MS, m/z: calculated for 2.3.[M+H] Analytic+ 576.9732, Methods found 576.9755 (Figure S4). Single crystals of 2 were prepared from a dichloromethaneThe MS data were at obtained RT by onslow a Bruker evaporation micrOTOF (Figure spectrometer S1). Comparison equipped with of the XRD and electrospray ionization (ESI) source. The NMR spectra were recorded on a Bruker AVANCE PXRD data showed that the phases coincide (Figure S8). 1 13 1 III 400 spectrometer at ambient temperature in CDCl3 (at 400, 101, 86 MHz for H, C{ H} and 195Pt NMR spectra, respectively). IR spectra were recorded on a Bruker TENSOR 272.2. FT-IR Crystallization spectrometer (4000–200 cm−1, KBr pellets) (Figure S3). Powder X-ray diffraction (PXRD)Single data were crystals measured of at room1·tbe temperature and 2·tbe using were a Bruker obtained D2 Phaser by Desktop slow X-ray evaporation of a diffractometer equipped with a CuKa1 + 2 source; the data were collected in the range of 2qdichloromethane= 5–80◦ with a step sizesolution of 0.02 ◦(1(2 qmL)). of a mixture of the corresponding 1 (0.002 mmol) or 2 (0.002 mmol) and tbe taken in an excess (0.87 mmol) at RT. Yellow crystals 2, 1·tbe and 2.4.2·tbe X-ray of Structure suitable Determination for XRD were and Refinement released after 3−4 d. Suitable single crystals were studied on a SuperNova Duo CCD diffractometer (Cu Ka2.3.(l =Analytic 1.54184), Methods mirror monochromator, w-scan). Crystals were incubated at 100 K during data collection. All structures were deciphered by direct methods using SHELXT [30] and refinedThe usingMS data SHELXL were [31 ].obtained All non-hydrogen on a Bruker atoms weremicrOTOF refined withspectrometer individual equipped with electrospray ionization (ESI) source. The NMR spectra were recorded on a Bruker AVANCE III 400 spectrometer at ambient temperature in CDCl3 (at 400, 101, 86 MHz for 1H, 13C{1H} and 195Pt NMR spectra, respectively). IR spectra were recorded on a Bruker TENSOR 27 FT-IR spectrometer (4000–200 cm−1, KBr pellets) (Figure S3).