Copper Complexes of 1,4-Naphthoquinone Containing Thiosemicarbazide and Triphenylphosphine Oxide Moieties; Synthesis and Identification by NMR, IR, Mass, UV Spectra, and DFT Calculations

New 1,4-naphthoquinone derived by triphenylphosphaneylidene (Ph3P) and N-substituted-hydrazine-1-carbothioamides were obtained during a one-pot reaction of 2,3-dichloro-1,4-naphthoquinone with thiosemicarbazides, Ph3P and in the presence of triethyl amine (Et3N) as a catalyst. The structure of the ligands was established by ESI, IR, and NMR spectra, in addition to elemental analyses and X-ray structure analysis. On subjecting the newly prepared ligands with CuCl2 and Ph3P, autoxidation occurs, and (E)-(2-(1,4-dioxo-3-(triphenyl phosphanylidene)-3,4-dihydronaphthalen-2(1H)-ylidene)carbamothioyl)hydrazinyl)-((triphenylphosphanyl)oxy)copper derivatives were formed in very good yields. The structure of the obtained complexes was proved by ESI, IR, NMR, and UV spectra, in addition to elemental analyses and theoretical calculations.

In the same manner, bisphosphonium salt containing a 1,4dihydroxynaphthyl-substituted moiety was synthesized in high yield by the reaction of 2-methyl-1,4-naphthoquinone with three equivalents of Ph 3 P and hydrogen bromide. 7 Metal-free synthesis of aryltriphenylphosphonium bromides by the reaction of Ph 3 P with aryl bromides in refluxing phenol was developed. 8 With the high reactivity of naphthoquinones, 2,3-dichloro-1,4-naphthoquinone (DCHNQ, 7) reacted with nucleophiles and substituted one or both chlorine atoms. 9−13 It was found that the reaction of 7 with p-nitrobenzhydrazide (9) in 1:2 or 2:l ratio in DMF gave only the disubstituted product, bis-(-p-nitrobenzhydrazino)-1,4-naphthoquinone (10). However, when an ethanolic solution of 7 and 9 was refluxed for 21 h, the main product was a bright red precipitate of 11 14 (Scheme 2).
Mass spectroscopy of 15f revealed [M + H] + at m/z = 564 (100), whereas the molecular ion peak appeared at m/z = 563 (30%). HRMS confirmed [M + H] + of compound 15f as C 33 H 31 N 3 O 2 P 1 32 S 1 . The 1 H NMR spectrum showed the two NH protons at δ H = 13.18 and 6.74. In the 1 H NMR spectrum, the butyl protons resonated as a double-doublet (J = 7.7, 1.5 Hz, 2H) and three multiplets at δ H = 3.58, 1.60−1.49, 1.35− 1.26, and 1.02−0.99 ppm, respectively. The 13 C NMR spectrum showed the carbonyl carbon signals at δ C = 186.1 and 185.9, whereas C=S resonated at 178.4 ppm. The butyl carbon signals resonated in the 13 C NMR spectrum at δ C = 44.6, 30.4, 20.1, and 14.0 ppm. IR spectroscopy displayed the NH-stretching at ν̃= 3340−3053 (w, ΝΗ), whereas the two carbonyl groups and C�N appeared at ν̃= 1586, 1521, and 1434, respectively. Besides, the C�P and the C�S groups appeared as strong bands in the IR spectra at ν̃= 1170 and 992 cm −1 , respectively. The structure of 15f was confirmed by Xray structural analysis, as shown in Figure 3.
In the crystal structures of 15c and 15f, are the bond distances and angles in the expected range with a slight delocalization of the π-electron in the thiosemicarbazide moiety (see cif-file). The thiosemicarbazide and 1,4-naphthoquinone moieties are coplanar.
The mechanism describes that the formation of 15a-f is based upon the addition of Ph 3 P to C-1 (or C-2) in 7 to give the Zwitterion 17, which would be in resonance with the intermediate 18 (Scheme 4). The addition of 14a-f in the presence of Et 3 N would then accompany the elimination of a molecule of HCl and another of Ph 3 P to give 19a-f (Scheme 4). Subsequently, the extruded Ph 3 P would again add to halogenated intermediates 19a-f to produce salts 20a-f (Scheme 4). Finally, a molecule of Et 3 N would facilitate the formation of 20a-f via the elimination of a molecule of triethylammonium hydrochloride. Interestingly, the reaction of equal equivalents of compounds 15a-f with Ph 3 P and CuCl 2 ·2H 2 O in ethanol at rt and for 1−3 d produced the Cu-complexes 16a-f (Scheme 5). Based on IR, 1 H NMR, and mass spectra, together with elemental analysis, the NH-3 proton of the thiosemicarbazone moiety, in 15a-f, was eliminated, and aerial oxidation occurred, as shown in Scheme 5.

Assignment of the Ligands 15a-f and Their Cu-Complexes 16a-f by Mass Spectroscopy and Elemental
Analyses. The molecular formulae of the obtained complexes were proved according to the mass spectroscopic data and the elemental analyses. Physical data from the color, m.p., and yield in g (%) were illustrated, as shown in Table 1.
Elemental analyses and mass spectra indicated that the formed Cu(II)-complexes 16a-f resulted in the sum of the molecular weight of compounds 15a-f with one copper atom together with a Ph 3 PO molecule. Elemental analyses of compounds 16a-f are shown in Table 2.
2.2. Assignment by IR Spectra. The significant bands in infrared spectra for both ligands 15a-f and their metal complexes 16a-f are represented in Table 3. The symmetrical stretching of NH bands for compounds 16a-f was absorbed in the region at their expected region of IR spectra. The shift in functional groups from the ligands to the corresponding complexes supported the chelating process. Coordination occurred via N-2 and the oxygen atom of Ph 3 P. The C�S stretching gave slight shifts in the case of a comparison between 15a-f and 16a-f. Most indicative is the new appearance of P�O, Cu−N, and Cu−O bands during the comparison between 15a-f and 16a-f. For example, IR spectroscopy of 15a showed the following bands at ν = 3345, 3052 for ΝΗ stretching, 1188 (as a strong band) for C� P, and 993 (as a strong band) cm −1 for s, C�S. In the case of 16a, the NH stretching was absorbed as a weak band at ν = 3054, whereas at ν = 1178, as a strong band for the C�P group. New bands were noted at ν = 1019 (m, P=O), 536 (s, Cu−N), and 457 cm −1 (s, Cu−O). Similar values of the previous three groups were previously reported. 24, 25 The same trend was also observed in all compounds 16b-f ( Table 2).

Assignment of the Complexes 16a-f by NMR Spectra.
Together with the elemental analyses, mass, and IR spectra, the chemical shift in NMR spectra, indicating the complexation process of 15a-f with Cu(II) to form 16a-f, as shown in Table 4. As it is known that although most NMR measurements are conducted on diamagnetic compounds, paramagnetic samples are also amenable to analysis and give rise to special effects indicated by a wide chemical shift range and broadened signals. 26,27 However, several papers reported the use of the Cu(II) complex with Ph 3 P of the composition CuCl 2 (PPh 3 ) 2 . 28−30 The previous studies showed that the oxidation state of II cannot be stabilized for copper in the presence of such a reducing ligand like Ph 3 P. Therefore, Cu(II) is converted into Cu(I) during complexation with Ph 3 P and compounds 15a-f. We here note that NMR spectra could be distinguished, and there are remarkable shifts in some values of the chemical shifts (δ) of 1 H NMR and 13 C NMR spectra of compound 15a, as an example, compared with its complex 16a. In the 1 H NMR spectrum, NH-2 resonated at δ H = 12.90, whereas NH-1 appeared at δ H = 5.77. The ethyl protons appeared as a quartet at δ H = 3.19 for CH 2 ethyl , whereas a triplet at δ H = 0.62 ppm (J = 7.1 Hz). In the case of 16a (Table 4), the 1 H NMR spectrum of only NH-1 at δ H = 5.49, whereas N-2 didn't reveal any proton. The ethyl protons appeared as a quartet at δ H = 4.05 (J = 7.1 Hz) and a triplet at δ H = 1.20 ppm (J = 7.1 Hz). The 13 C NMR spectrum of 15a showed the carbonyl carbon signals at δ C = 183.7 and 183.6, whereas C�S resonated at δ C = 176.7 ppm. The ethyl carbons appeared at δ C = 37.9 for CH 2 and at δ C = 13.5 ppm for CH 3 (as shown in the Supporting Information). In the case of 16a, in the 13 C NMR spectrum, the carbonyl carbon signals resonated at δ C = 186.0 and 183.6 ppm. (C q , CO), whereas the C�S carbon signal appeared at δ C = 175.4 ppm. The ethyl carbon signals resonated at δ C = 39.0 (CH 2 ethyl ) and 13.6 ppm (CH 3 ethyl ). Significantly, the exocyclic carbon signal (in C�N) appeared in the 13 C NMR spectrum of 15a at δ C = 142.8, whereas for 16a, it appeared at δ C = 143.1.

UV−Vis Studies.
UV−vis absorption spectra of the Cu(II) complexes 16a-f were measured from 200 to 800 nm, using acetonitrile. The blue-colored compounds exhibited bands in UV−vis spectra, ranging from 540 to 548 nm (i.e., n−π*). These bands can be attributed to ligand-to-metal charge transfer transitions from nitrogen to Cu(II). N → Cu ← O bands are common in electronic spectra of metal complexes of thiosemicarbazides. Representative examples are the UV/vis spectra of compounds 16b and 16c (Figure 4). In the field of inorganic chemistry, UV/Vis spectra are usually associated with d−d transitions and colored transition metal complexes.

Optimized Geometries.
To verify the experimental findings, the complexes under study were optimized and are illustrated in Figure 5. No imaginary frequencies were noticed for the optimized complexes, ensuring that the obtained geometries were true minima. The energy differences (ΔE) between the investigated complex (E) and the most stable one (E 1 ) are also given in Figure 5. The single point energies ensured the further favorability of complex 1 over other studied conformations.
2.6. HS Analysis. HS analysis was considered a dependable technique to qualitatively elucidate intermolecular interactions within crystal structures and unveil the interactions around the molecules' surface. 31−34 HSs, including the d norm and its associated 2D fingerprints, shape index, and curvedness, were mapped for the studied complexes. Figure 6 shows the d norm map and the associated 2D fingerprint plots. The extracted shape index and curvedness maps are illustrated in Figure 7.
As shown in Figure 6(i), the C···H/H···C contacts were noticed with obvious large red regions labeled 1 and exhibited 27.0% of the total HS area. Such contacts were also observed in the 2D fingerprint plots as a pair of symmetrical spikes at (d e + d i ) ∼ 2.6 Å (Figure 6(ii)).
The existence of red regions dubbed 2 in the HSs mapped over the d norm property could be attributed to the occurrence of the reciprocal O···H/H···O contacts that were found in the 2D fingerprint plots at (d e + d i ) ∼ 2.3 Å. For S···H/H···S contacts (labeled 3), prominent red regions were noticed with 2.1% of the total HS area and characterized by spikes at (d e + d i ) ∼ 2.7 Å. The N···H/H···N contacts were observed with label 4, as white and red regions in the d norm maps, with a 2.1% contribution.  Conspicuously, the HSs mapped over the shape index and curvedness properties (Figure 7) confirmed the occurrence of the C···H/H···C, O···H/H···O, S···H/H···S, and N···H/H···N interactions by the existence of the complementary pair of red and blue triangles in the shape index and the flat green area in curvedness.

EXPERIMENTAL SECTION
Uncorrected Melting points were taken in a Gallenkamp melting point apparatus (Weiss-Gallenkamp, Loughborough, UK). The infrared spectra were recorded with the Bruker, IFS 88 instrument. Solids were measured by the attenuated total reflection (ATR) method. The positions of the respective transmittance bands are given in wave numbers υ ̅ [cm −1 ] and were measured in the range from 3600 to 500 cm −1 . All UV− Vis spectra were recorded on the Specord 50 Plus made by the company Q Analytik Jena (Thuringia, Germany). The NMR spectra of the title compounds described herein were recorded on a Bruker Avance 400 NMR instrument at 400 MHz for 1 H NMR and 101 MHz for 13 C NMR, and the references used were the 1 H and 13 C peaks of the solvent, acetone-d 6 : 2.05 ppm for 1 H NMR, and 206.26 ppm for 13 C{ 1 H}NMR spectra. For the characterization of centrosymmetric signals, the signal's median point was chosen; for multiplets, the signal range was given. The following abbreviations were used to describe the proton splitting pattern: d = doublet, t = triplet, m = multiplet, and dd = doublet of a doublet. The following abbreviations were used to distinguish between signals: H Ar = aromatic-CH. Signals of the 13 C NMR spectra were assigned with the help of DEPT90 and DEPT135 and were specified in the following way: + = primary or tertiary carbon atoms (positive DEPT signal), − = secondary carbon atoms (negative DEPT signal), C q = quaternary carbon atoms (no DEPT signal). Mass spectra were observed by FAB (Fast atom bombardment) experiments and were recorded using the Finnigan, MAT 90 (70 eV) instrument. Elemental analyses were performed on the Elementar Vario MICRO instrument. TLC silica plates coated with a fluorescence indicator from Merck (silica gel 60 F254, thickness 0.2 mm) were used to purify the crude products, and flash chromatography with Silica gel 60 (0.040 × 0.063 mm, Geduran) (Merck) was used. Solvents, including acetone-d 6 , were purchased from Merck without further drying.

General Procedures.
Compounds 14a-f were prepared according to the literature. 23 3.1.1. General Procedure for the Synthesis of Ligands 15a-f. 2,3-Dichloro-1,4-naphthoquinone (7) (250 mg, 1.10 mmol, 1.10 equiv) was added to a stirred solution of substituted hydrazinecarbothioamides (14a-f) (1.00 mmol, 1.00 equiv) in 10 mL of dry CH 3 CN. The resulting solution was stirred at room temperature for 16 h. After S-alkylation was complete (i.e. the reaction was followed up by TLC), the dried salt was redissolved in dry CH 3 CN, after which Et 3 N (1.10 mmol) and Ph 3 P (1.10 mmol) were added. The resulting mixture was left under reflux for about 13−16 h. The reaction mixture was left to cool at room temperature, distilled H 2 O (50 mL) was added, and the resulting solution was extracted with CH 2 Cl 2 . The organic extracts were dried over anhydrous CaCl 2 , filtered, and evaporated. The crude material was purified by flash-chromatography using cyclohexane/ethyl acetate (4:1) to give compounds 15a-f.               Figure 6. Views of (i) HSs mapped over the d norm property; the labels 1, 2, 3, and 4 represent C···H/H···C, O···H/H···O, S···H/H···S, and N···H/ H···N contacts, respectively; and (ii) 2D fingerprint plots for the interactions above.

ACS Omega
http://pubs.acs.org/journal/acsodf Article 2H 2 O (0.170 g, 1.00 mmol, 1.00 equiv) and Ph 3 P (0.262 g, 1.00 mmol, 1.00 equiv) in 40 mL of absolute EtOH was stirred at room temperature for about 2−4 h (the reaction was monitored by thin-layer chromatography). After removal of the solvent under reduced pressure, the crude product was purified by column chromatography using EtOAc/hexane (5:1) to afford compounds 16a−f.

Geometrical Optimization and Energy Calculations.
Various quantum mechanical calculations were carried out to confirm the experimental results. The studied complexes were first optimized at the B3LYP/6-31G* level of theory. 37,38 The vibrational frequency and single-point energy calculations were performed upon the optimized geometries. All the adopted quantum mechanical calculations were executed at the B3LYP/6-31G* level of theory with the help of Gaussian 09 software. 39 4.2. HS Analysis. In the current study, HS analysis 40 was executed to give an in-depth qualitative insight into the role of the main intermolecular interactions. Using HS analysis, the normalized contact distance (d norm ) surface was mapped over a fixed color scale ranging from red (−0.05 au) to blue (+0.75 au). The fingerprint plots were generated using the translated 1.0−2.8 Å range, and reciprocal contacts were considered. Moreover, the shape index and curvedness properties were mapped with the color range of −1.0 au (concave) to 1.0 au (convex) and a range of −4.0 au (flat) to 0.40 au (singular), respectively. The generated HSs and the associated 2D fingerprint plots were extracted using the CrystalExplorer17 software. 41
NMR ( 1 H NMR and 13 C NMR), IR, and mass spectra, in addition to HRMS spectra of compounds 15a-f and 16a-f; figures of UV Spectra of compounds 16a-f; and Xray figures and structural data and of compounds 15c and 15f (PDF)