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Chloride Cluster with Diselenide Countercations: Application in CS Cross Coupling Reactions

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Chloride Cluster with Diselenide Countercations: Application in CS Cross Coupling Reactions Journal of Organometallic Chemistry 884 (2019) 29e35 Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem Anionic Bismuth(III) chloride cluster with diselenide countercations: Application in C-S cross coupling reactions * Prabusankar Ganesan , Adinarayana Mannem, Nirmala Muthukumaran Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi, Telangana, 502 285, India article info abstract Article history: The first weakly coordinating anion (WCA) with reactive p-block cation (rPBC) type of Received 28 November 2018 4- 2þ [(Bi4Cl16) {(LSeSeL) }2], L ¼ 1,3-bis(2-benzhydryl-4,6-dimethylphenyl)-1H-imidazole-2(3H), ion pair is Received in revised form reported. The tetranuclear anionic bismuth(III) cluster shows a new type of ladder structure with two 17 January 2019 different types of Bi(III) coordination modes. In the solid state structure, the tetranuclear bismuth(III) Accepted 23 January 2019 cluster is sandwiched by two diselenide cations through hydrogen bonding interactions. Besides, this ion Available online 28 January 2019 pair has been efficaciously employed as catalyst in C-S cross-coupling reactions under optimized reaction condition. This ion pair depicted a wide range of substrate scope with different thiols and aryl halides. Keywords: © Bismuth 2019 Elsevier B.V. All rights reserved. Selone Ion pair C-S cross-coupling 1. Introduction established, the weakly coordinating anion (WCA) with reactive p- block cations (rPBC) class of pair is not known [22]. The N-heterocyclic carbene (NHC) analogues of chalcogenones Thus, we now report the isolation of first bismuth tetra anionic (S, Se, Te), have depicted the upsurge growth in the field of salt as WCA with semi-super bulky bis-1,3-diimidazole diselenide organometallic chemistry owing to their potential applications in as rPBC from the direct oxidation of 1,3-bis(2-benzhydryl-4,6- supramolecular [1], medicinal [2] and materials chemistry [3e6]. dimethylphenyl)-1H-imidazole-2(3H)-selenone (1) by BiCl3.In Especially, the oxidation of imidazole selone is known as the pivotal addition, the application of WCA-rPBC pair in C-S cross coupling reaction in the metabolism of several biological process [7]. Such reactions are demonstrated. oxidation of 1,3-disubstituted imidazole was carried out under suitable conditions using suitable oxidizing agents such as 7,7’,8,8’- 2. Results and discussion tetracyano-p-quinodimethane [8]orI2 [9,10] or Te or ICl or IBr [8,11] e e or Br2 [12 14] or HCl/air [15 17]. Several 1,3- disubstituted imid- 2.1. Synthesis and characterization of 1 and 2 azole diselenide dications have been isolated and most of them are structurally characterized [18]. However, the metal catalyzed Organo imidazolin-2-selone ligand 1 with spatially defined oxidation of 1,3-disubstituted imidazole selone or thione has not steric impact was synthesized in very good yield from the reaction been realized until 2011 [19]. The first triflate salts of 1,3- between 1,3-bis(2-diphenylmethyl-4,6-dimethylphenyl)-imidazo- disubstituted imidazole disulfide dications or diselenide dications lium chloride and elemental selenium powder in the presence of have been derived using Cu(OTf)2 [20]. Later, the oxidative reaction activated K2CO3 in methanol (Scheme 1)[23]. In solution state, 1 ’ ¼ of sterically crowded IPrSe or IPr Se (IPr {(HCN(C6H3-iPr2- adopts two different conformations with 2:1 ratio. The mixture of ’ ¼ 2,6))2C}; IPr [(HC)2{N(C6H3-iPr2-2,6)}{NCH2C(O)OMe}C}] by two conformations was obtained in deuterated chloroform solu- e $ Bi(OTf)3 or Cu( ClO4)2 6H2O was reported to isolate [(IPr) tion. However, the identity of each rotamer was very complicated. þ þ 2 - ‘ 2 1 13 Se]2 { OTf}2] or [(IPr )Se]2 {-O4Cl}2], respectively [21]. Although In NMR analysis, H and C spectra gave complicated splitting and the metal salt route to imidazole diselenide dication is well related information due to free rotation around C-N bond slowing the interchange between conformations. The rotamers of the ligand was confirmed by FT-IR, multinuclear (1H and 13C) NMR, and TGA. ¼ * Corresponding author. In molecule 1, the FTIR stretching frequency for C Se was located À1 1 E-mail address: [email protected] (P. Ganesan). at 1266 and 1167 cm . Upon seleniation, the H NMR signal for the https://doi.org/10.1016/j.jorganchem.2019.01.017 0022-328X/© 2019 Elsevier B.V. All rights reserved. 30 P. Ganesan et al. / Journal of Organometallic Chemistry 884 (2019) 29e35 bridged chloride ions. The geometry of Bi(1) can be described as square pyramidal geometry. The Bi(2) center in 2 is fulfilled by three terminal, two doubly bridged and one triply bridged chloride ions. The geometry of Bi(2) can be considered as octahedral. The dis- elenide fragment Se‒Se is connected by two semi bulky imidazole ligands. The terminal BieCl bond distances around Bi(1) and Bi(2) are not comparable. The Bi(1)eCl(7) depicts the shortest bond dis- tance while Bi(2)eCl(1) shows the longest bond distance. The ter- minal BieCl bond lengths are shorter than the bridging BieCl bond distances. The Se‒Se bond lengths in 2 is 2.345(12) Å, which is slightly shorter than the presciently reported [{(HCN(Me))2C- 2þ e 2þ Se}2] [{ OTf}2]2.360(7)Å[25], [{(HCN(Me))2CSe}2] {I}2] þ (2.434(2) Å), [{(HCN(Me))2CSe}2Cl] {I3}] (2.440(2) Å) [26] and [ IPrSe(OTf)2]2 2.427(5) Å [21]. The CeSe bond lengths in 2 is com- parable and slightly shorter than IPr*Se (1.942(16) Å) [27]. As shown e …. Scheme 1. Synthesis of 1. in Fig. 2, the WCA and rPBC are held together through C H Cl … (2.727(1) and 2.837(1) Å) and Se .N (2.782(1)-2.849(1) Å) hydrogen 4- bonding interactions. The WCA, [Bi2Cl16] is sandwiched by two acidic N(CH)N protons (around d ¼ 10.5e12.0) present in 1,3-bis(2- rPBC diselenides (Fig. 3). benzhydryl-4,6-dimethylphenyl)-1H-imidazolium chloride was absent in imidazolin-2-selone (1). In 13C NMR, the carbene carbon 2.1.1. Thermogravimetric analysis attached to selenium shows two signals at d ¼ 159.1 and 158.1. Stability of 2 was accomplished by thermogravimetric analysis Subsequently, the tetra nuclear bismuth(III) selone complex 2 (TGA) and compared with 1 (Fig. 4). 1 depicted a clear two stage was synthesized from the reaction between BiCl3, and an equimolar weight losses from 290 Cto440 C with 79% weight loss then 21% quantity of organo selone (1) in toluene at room temperature weight loss from 440 C to 620 C, which can be attributed to the (Scheme 2). The complex 2 was isolated as orange red precipitate decomposition of organic moieties followed by selenium. The with good yield. 2 is soluble in highly polar organic solvents like molecule 2 showed considerable stability till 290 C then gradual methanol, acetonitrile and dimethyl sulfoxide, while insoluble in weight loss till 770 C with 84% weight loss due to the decompo- dichloromethane, chloroform and petroleum ether. 2 is stable un- sition of organic moieties. The remaining 16% residue can be 1 der ambient condition. The H NMR chemical shift values of 2 are attributed to the Bi2Se3 material. almost similar to that of 1. The 13C NMR chemical shift value of C¼Se in 2 showed d 1e3 2.2. Catalysis upfield shift compared to that of 1. The solid state structure of 2 was further confirmed by single crystal X-ray diffraction technique. The 2.2.1. C-S cross coupling reactions suitable single crystals for the X-ray analysis of 2 were isolated from Transition metal catalyzed cross-coupling reactions have found the saturated solutions of acetonitrile at room temperature (Table widespread popularity in synthetic chemistry [28]. The C‒S bond 1). The X-ray crystallographic analyses of 2 suggests that the syn plays an important role in numerous compounds for biological and conformer is preferred in the solid state due to intermolecular in- pharmaceutical applications as well as for the precursor based teractions [23]. materials chemistry [29e39]. The traditional methods for C‒S bond 2 is a rare example for the weakly coordinating anion (WCA) formation often employs the harsh conditions [29h]. For example, with reactive p-block cations (rPBC) class of pair. The tetra anionic the coupling of thiolates with aryl halides takes place in hexame- 4- tetranuclear bismuth(III) chloride cluster, [Bi2Cl16] is stabilized by thylphosphoramide at 200 C. The reduction of sulfoxide/sulfone is 4- the two diselenide counter cations (Fig. 1). Interestingly, [Bi2Cl16] carried out with strong reducing agents like DIBAL-H and LiAlH4 in 2 shows an unusual structural motive with two different types of [40,41]. To overcome such drawbacks, considerable research on the coordination environment around bismuth(III) centers. development of catalytic systems for the C‒S cross-coupling of 4- The possible mechanism for the formation of [Bi4Cl16] can be thiols with aryl halides have been developed. In 1978, Migita and 2- rationalized through the formation of edge-edge dimer [Bi2Cl8] co-workers reported the first CeS cross-coupling of aryl halides - from J-square-based pyramidal [BiCl4] unit with retention of lone- with thiols using tetrakis(triphenylphosphine)-palladium as cata- 2- pair electrons (Scheme 3)[24]. Further dimerization of [Bi2Cl8] lyst [30]. Later, several metal catalysts in which palladium [31], 4- anions could lead to the formation of [Bi4Cl16] anions, which got nickel [32], cobalt [33], copper [34], rhodium [35], indium [36], zinc trapped by two semi-super bulky diselenide cations.
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