Coordination of O-Propyl-N-phenylthiocarbamate to HgI₂ and the Crystallographic Characterization of an Anilinium Chloride Thiocarbamate Adduct

Abstract

In order to investigate the coordination chemistry of O-alkyl N-aryl thiocarbamate ligands, HgI₂ was reacted with one equivalent of PrOC(=S)N(H)Ph L in toluene solution to afford the 1D polymeric title compound [{IHg(μ-I)}{κ¹-PrOC(=S)N(H)Ph}]_n CP1. The formation of this iodide-bridged coordination polymer was ascertained by a single-crystal X-ray diffraction study performed at 100 K, as well as the formation of an adduct between anilinium chloride and L forming a supramolecular ribbon of composition [L(PhNH₃)(Cl)]. The occurrence of anilinium chloride is due to the partial hydrolysis of L in the presence of HCl.

1. Introduction

N-aryl-O-alkyl thiocarbamate ROC(=S)N(H)Ar constitute valuable intermediates in organic synthesis and these organosulfur compounds cover a wide range of applications, going from biological and pharmacological activity to catalysis [1,2,3,4,5,6]. Furthermore, they are also more and more used as ligands in coordination chemistry, since the soft C=S thione function (according Pearson’s HSAB principle) [7] readily coordinates to numerous transition metals complexes with Cu(I), Ag(I), Hg(II), Ru(II), Rh(III), etc. [8,9,10,11]. Although most of these complexes are mononuclear, we have recently communicated the characterization of the dinuclear species [{I₂Bi(μ₂-I)₂BiI₂}{κ¹-MeOC(=S)N(H)Ph}₄] and that of the 1D-coordination polymers [{Cu(μ₂-X)₂Cu}{μ₂-MeOC(=S)N(H)Ph}₂]_n (X Br, I) [12,13,14]. Some crystallographically characterized complexes ligated by O-alkyl-N-aryl thiocarbamates are presented in Scheme 1 [2,8,12].

Since some of our previously reported compounds ligated with MeOC(=S)N(H)Ph present only a limited solubility in common solvents, we decided to synthesize the already literature-known derivative PrOC(=S)N(H)Ph [15,16,17], which should assure, due its longer alkoxy chain, a better solubility. Furthermore, we are not aware of any metal complex bearing this thione-type ligand L. We therefore reacted HgI₂ with O-propyl-N-phenyl thiocarbamate and describe therein the crystal structure of the isolated coordination polymer. This research is a continuation of our investigations on the coordination chemistry of thioether and thione-type ligands on Hg(II) centers [18,19,20,21].

2. Results and Discussion

The synthesis of PrOC(=S)N(H)Ph L has already been communicated by Tiekink et al., who obtained this thiocarbamate by the nucleophilic addition of in situ-generated sodium propanolate to phenylisothiocyanate, followed by acidic hydrolysis and extraction with CHCl₃ (Scheme 2) [16]. We applied the same protocol, but instead of performing the extraction 1 h after acidic hydrolysis with an excess of 2N HCl, we allowed the reaction mixture to stir overnight. According to the protocol in the literature, we then partially evaporated the chloroform extract, yielding a large amount of a yellowish, somewhat gluey solid. We picked up some yellowish crystals embedded in the crude product and noticed after a fast scan that the crystal parameters did not match with those reported by Tiekink et al. for crystalline L, which forms a dimer associated through strong N-H···S hydrogen bonds, giving rise to an eight-membered thioamide cycle. We therefore undertook a full crystal structure determination at 100 K, revealing a co-crystallization of L with anilinium chloride in a 1:1 ratio (Figure 1). The chloride anion of this anilinium salt, which probably originates partially from the hydrolysis of L after prolonged contact with aqueous HCl, interacts via hydrogen bonding with the three H atoms of the protonated aniline. The N2-H···Cl distances vary between 2.21 and 2.34 Å (d(N2···Cl¹) 3.2087(15) Å; d(N2···Cl) 3.1157(14) Å; d(N2···Cl²) 3.1862(15) Å), and are somewhat looser than those reported for pure anilinum chloride (2.08–2.14 Å). Note that this latter salt is reported to form a layered supramolecular structure with R₆₃(12) rings [22,23]. In the case of [L(PhNH₃)(Cl)], there is an additional bonding between the N1-H1 group of the thiocarbamate and the Cl¹ ion of 2.47 Å. Thus, a 1D supramolecular ribbon is generated. However, in contrast to the dimeric association reported for pure L, no secondary interactions between the thiocarbamate molecules are observed.

The ¹H NMR of pure recrystallized L recorded in CDCl₃ reveals at ambient temperature a broad signal at δ 4.56 for the OCH₂ group, whereas the CH₃ and CH₂ resonances are well resolved, appearing as a triplet and a sextet with a coupling constant of 7.2 Hz. Furthermore, the broad N-H resonance is found at δ 8.59 ppm. An indication of dynamic processes occurring in solution is provided by the ¹H NMR spectrum of L recorded at 323 K, in which the OCH₂ resonance at δ 4.56 appears now as a resolved triplet (Figure 2). There is also a slight low-field shift in the N-H signal. This dynamic behavior is probably due to a hindered rotation around the C-N bond, giving rise to conformational isomers. In the ¹³C{¹H} NMR spectrum of L, the thiocarbonyl carbon is observed at δ 188.9 ppm, and the oxygen-bonded methylene group is observed at δ 74.8 (Figure 3).

The hitherto unknown polymeric HgI₂ complex [{IHg(μ-I)}{κ¹-PrOC(=S)N(H)Ph}] CP1 shown in Scheme 2 was straightforwardly formed by adding at ambient temperature an equimolar amount of L to a slurry of HgI₂ in toluene. The orange-red suspension gradually dissolved after 2 h to give a homogenous solution. After layering with heptane, yellow-orange crystals were formed. This air-stable product is only partially soluble in CDCl₃, but the ¹H NMR spectrum clearly reveals a shift in the NH signal at δ 9.43 ppm to a lower field with respect to uncoordinated L (Δδ 0.84 ppm).

Since according to a survey in the literature only two tetrahedral molecular HgCl₂ complexes ligated by thiocarbamates have been crystallographically characterized yet [22,24], we examined the product crystallizing in the monoclinic space group P2₁/c by an X-ray diffraction study performed at 100 K. As shown in Figure 4, a polymeric species has formed, in which the crystallographically identical coordinated Hg(II) centers are linked mutually through a μ₂-bridging I2 iodido ligand. The Hg···Hg separation of 4.22 Å excludes any intermetallic interaction.

The tetrahedral coordination sphere around each Hg atom is completed by a terminal I1 ligand and a S-bound thiocarbamate ligand. The Hg–S bond length of 2.5438(9) Å is significantly longer than the mean values of 2.44(1) and 2.499(1) Å reported for dichloro-bis(O-ethylthiocarbamato)mercury and dichloro-bis[O-ethyl(2,6-dimethylphenyl)thiocarbamato]mercury [22,24]. For comparison, for dinuclear bis[μ-iodo(thiobenzamide)mercury], a Hg–S bond length of 2.467(2) Å has been determined [25].

The C=S bond is slightly elongated with respect to that of non-ligated PrOC(=S)N(H)Ph (1.710(4), vs. 1.6697(16) Å). The bridging I2 atoms are quite symmetrically bridging, with the mean Hg–I_bridg bond distance of 2.875 Å being far longer than the Hg–I_term one (2.875 Å vs. 2.6829(3) Å). For the above-mentioned compound asymmetrical iodido-bridged [{IHg(μ₂-I)}{κ¹-thiobenzamide]₂, the respective Hg–I distances are 2.818(1), 3.201(1) and 2.673(1) Å [25]. At first glance, the 1D architectures of CP1 and copper(I) analogue [{Cu(μ₂-I)₂Cu}(μ₂-EtOC(=S)N(H)Ph})₂]_n [15] are somewhat similar, but a closer look reveals some striking differences. The unidimensional ribbon of [{Cu(μ₂-I)₂Cu}{μ₂-EtOC(=S)N(H)Ph}₂] is doubly bridged by both μ₂-I atoms and bridging EtOC(=S)N(H)Ph ligands, bringing the metal centers into much closer contact. Furthermore, in the Cu(I) polymer chain, the N-H groups weakly interact with the μ₂-I atoms through an intramolecular N-H···I bonding of 2.778 Å, whereas in CP1, the shortest N-H···I contact is 3.143 Å

In the packing, no interchain interactions occur. Furthermore, as shown in Figure 5, loose intramolecular S···H and O···H contacts occur. Upon further examination of the molecular arrangement within the solid-state structure, it is noted that the polymer chain extends along a translational c glide symmetry. This is evident from the bonding of the HgI₂ salts with the respective thiocarbamate ligands. The positions of these ligands alternate along the glide plane, while no significant intermolecular interactions, e.g., N1-H···Hg1, occur.

3. Experimental Methodology

Synthesis of CP1—To a slurry of HgI₂ (454 mg, 1.0 mmol) in 10 mL of toluene, O-propyl N-phenylthiocarbamate L (195 mg, 1 mmol) was added in several portions. HgI₂ dissolved progressively and the reaction mixture was stirred at room temperature for 2 h. Then, the solvent was allowed to evaporate partially to about 6 mL. After layering with heptane, yellow-orange crystals of CP1 were formed and then collected by filtration. Yield: 72%. Anal. Calc. for C₁₀H₁₃HgI₂NOS (M.W. = 649.68 g·mol⁻¹): C, 18.49; H, 2.02; N, 2.16; S, 4.94%. Found: C, 18.32; H, 1.98; N, 2.11; S, 4.76%. IR-ATR: 1230 ν(C=S), 1483 ν(C–N), 1548 ν(N–H), 3281 ν(N–H bonded) cm⁻¹.

Data collection for L and CP1 was performed on Bruker D8 Venture four-circle diffractometers from Bruker AXS GmbH (Karlsruhe, Germany). CPAD detectors used were Photon II (MoK_α) and Photon III (AgK_α) from Bruker AXS GmbH; X-ray sources: Microfocus source IµS; and microfocus source IµS Mo and Ag, respectively, from Incoatec GmbH with mirror optics HELIOS and a single hole collimator from Bruker AXS GmbH. Programs used for data collection were APEX4 Suite [26] (v2021.10-0) and integrated programs SAINT (V8.40A; integration) as well as SADABS (2018/7; absorption correction) from Bruker AXS GmbH [27]. The SHELX programs were used for further processing [28]. The solution of the crystal structures was achieved with the help of the program SHELXT [29], the structure refinement was achieved with SHELXL [30]. The processing and finalization of the crystal structure data was carried out with program OLEX2 v1.5 [31]. All non-hydrogen atoms were refined anisotropically. For the hydrogen atoms, the standard values of the SHELXL program were used with U_iso (H) = –1.2 U_eq(C) for CH₂ and CH and with U_iso (H) = –1.5 U_eq(C) for CH₃. All H atoms were refined freely using independent values for each U_iso(H).

Crystal data for C₁₆H₂₁ClN₂OS L include the following: M = 324.86 g∙mol⁻¹, colorless crystals, crystal size 0.343×0.287×0.156 mm³, monoclinic, space group P2₁/n, a = 10.8275(14) Å, b = 5.6092(8) Å, c = 27.626(3) Å,), α = 90°, β = 94.473(5)°, γ = 90°,V = 1672.7(4)ų, Z = 4, D_calc = 1.290 g/cm³, T = 100 K, λ = 0.71073, R₁ = 0.0343, Rw₂ = 0.0838 for 43376 reflections with I ≥ 2σ(I) and 3412 independent reflections. Largest diff. peak/hole/e Å⁻³ 0.52/–0.22. A multi-scan absorption correction was applied; T_max = 0.4891, T_min = 0.3440.

Crystal data for C₁₀H₁₃HgI₂NOS CP1 include the following: M = 649.66 g∙mol⁻¹, orange crystals, crystal size 0.216 × 0.169 × 0.117 mm³, monoclinic, space group P2₁/c, a = 11.0287(7) Å, b = 17.3343(10) Å, c = 8.0027(5)Å), α = 90°, β = 101.7353(16)°, γ = 90°, V = 1497.93(16)ų, Z = 4, D_calc = 2.881 g/cm³, T = 100 K, λ = 0.56086, R₁ = 0.0215, Rw₂ = 0.0473 for 73399 reflections with I > = 2σ(I) and 4604 independent reflections. Largest diff. peak/hole/e Å⁻³ 1.55/–1.15. A multi-scan absorption correction was applied; T_max = 0.5624, T_min = 0.3964.

Data were collected using graphite-monochromated MoK_α radiation λ = 0.71073 Å and AgK_α radiation λ = 0.56086 Å. The structures were solved by intrinsic phasing and refined by full-matrix least-squares against F². Data have been deposited at the Cambridge Crystallographic Data Centre as CCDC 2382124 (L) and CCDC 2382127 (CP1) (Supplementary Materials). The data can be obtained free of charge from the Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/getstructures (accessed on 18 November 2024).

4. Conclusions

We have crystallographically evidenced that the reaction of PrOC(=S)N(H)Ph L with HgI₂ in a 1:1 ratio affords the 1D polymeric title compound [{IHg(μ-I)}{κ¹-PrOC(=S)N(H)Ph}]_n CP1. We are currently investigating whether changing the metal-to-ligand ratio may lead to a mononuclear tetrahedral species [HgI₂{PrOC(=S)N(H)Ph}₂] that is similar to complex A shown in Scheme 1. We are also extending our investigation to other HgX₂ and CdX₂ salts.