Synthesis and reactivity of thiosemicarbazone palladacycles. Crystal structure analysis and theoretical calculations

Inorganica Chimica Acta 449 (2016) 20–30

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Synthesis and reactivity of thiosemicarbazone palladacycles. Crystal structure analysis and theoretical calculations Javier Martínez a,⇑, Enrique M. Cabaleiro-Lago b, Juan M. Ortigueira c, M. Teresa Pereira c, Pablo Frieiro c, Fátima Lucio c, José M. Vila c,⇑ a b c

Departamento de Química Analítica e Inorgánica, Facultad de Ciencias Químicas, Universidad de Concepción, Casilla 160-C, Concepción, Chile Departamento de Química Física, Universidad de Santiago de Compostela, 27002 Lugo, Spain Departamento de Química Inorgánica, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain

a r t i c l e

i n f o

Article history: Received 19 October 2015 Received in revised form 15 February 2016 Accepted 30 March 2016 Available online 20 April 2016 Keywords: Cyclometallation Thiosemicarbazones Palladium Diphosphines Crystal structure DFT calculations

a b s t r a c t Reaction of the thiosemicarbazones 3-FC6H4C(Me)@NN(H)C(@S)NHR, (R = Et, a; Ph, b) with potassium tetrachloropalladate(II) in ethanol, lithium tetrachloropalladate(II) in methanol or palladium(II) acetate in acetic acid gave the tetranuclear cyclometallated complexes [Pd{3-FC6H3C(Me)@NN@C(S)NHR}]4 (1a, 1b). Reaction of 1a, 1b with the tertiary phosphines dppm, dppe, dppp, dppb or trans-dppen in 1:2 M ratio gave [(Pd{3-FC6H3C(Me)@NN@C(S)NHR})2(l-PPh2(CH2)nPPh2)], (n = 1, 2a–b; 2, 3a–b; 3, 4a– b; 4, 5a–b), [(Pd{3-FC6H3C(Me)@NN@C(S)NHR})2(l-PPh2CH@CHPPh2)], (6a–b). Treatment of 1a, b with dppm in 1:4 M ratio gave the mononuclear complexes [Pd{3-FC6H3C(Me)@NN@C(S)NHR} (Ph2PCH2PPh2-P)] (7a–b). Reaction of the latter with an equimolar amount of [PdCl2(PhCN)2] gave [PdCl2{Pd[3-FC6H3C-(Me)@NN@C(S)NHR](PPh2CH2PPh2)-P,S}], (8a–b). The molecular structure of ligands a and b, and of complex 6a have been determined by X-ray diffraction analysis. The ligands and complexes have also been characterized by Density Functional Theory (DFT) calculations in order to obtain structural information for the species for which no X-ray data were available. Ó 2016 Elsevier B.V. All rights reserved.

1. Introduction Thiosemicarbazones are very interesting ligands due to the varied properties they possess such as potential antitumoral, antimicrobial, and antifungal drugs as well as analytical reagents to determine, fix and entrap heavy metal ions [1–6]. Both biological activity and analytical properties are closely associated to their complexing ability, to their reactivity enhancement after coordination and to a tendency to take part in template reactions on matrices of transition metal ions [7–12]. The subsequent reactions are controlled by the structural features as ligands, the nature of substituents, the arrangement and space orientation of their complexing groups, and the mutual effect of ligands in the metal coordination sphere. Thiosemicarbazones usually coordinate to the metal through the imine nitrogen and the sulfur atom [13,14], although there are ligands with more than two donors, the number of which ⇑ Corresponding authors. E-mail addresses: [email protected] (J. Martínez), [email protected] (J.M. Vila). http://dx.doi.org/10.1016/j.ica.2016.03.044 0020-1693/Ó 2016 Elsevier B.V. All rights reserved.

depends on the aldehyde or ketone, and on the tautomeric equilibrium of the thiosemicarbazone [15,16]; more often than not sulfur coordinates in the thiolic form [13–16,1,17]. In thiosemicarbazone palladacycles the organic ligand binds tightly to the metal as terdentate [C,N,S] in a tetranuclear [18] structure through PdASchelating and PdASbridging bonds. The strength of the former bond is put forward in the reactivity of the palladacycles with nucleophiles, where even treatment with strong chelating tertiary diphosphines yields complexes with the ligand in a [C,N,S] fashion and a mono-coordinated diphosphine; the ensuing complexes perform as [P,S] metalloligands. Herein, we report the synthesis and reactivity of 3-fluorinated thiosemicarbazone palladacycles: the initial tetranuclear complexes bearing the two-fused chelate ring system at palladium [19–26] were treated with tertiary diphosphines to yield new mononuclear and dinuclear metallacycles as a function of the applied molar ratio. The former species behave as metalloligands and they are the starting materials for the preparation of new bimetallics. Structural information for those substances where crystal structure analysis was not possible was obtained from DFT calculations.

J. Martínez et al. / Inorganica Chimica Acta 449 (2016) 20–30

2. Results and discussion Although the compounds depicted hererin are similar to others reported by us [18,19,22,26,27] we sought to carry out DFT calculations in order to complement the diffractometric analysis when this is not possible, thus substantiating the suggested structures on the sole basis of spectroscopic data. Thiosemicarbazones a and b were prepared by reaction of 4ethyl-3-thiosemicarbazide and 4-phenyl-3-thiosemicarbazide with 30 -fluoroacetophenone, which were fully characterized (see Section 7). The NHR and NH groups gave rise to characteristic m (NAH) bands in the IR spectra ca. 3350 and 3250 cm1, the latter disappeared in the spectra of the complexes; the typical m(C@N) and m(C@S) stretches appeared in the ranges 1604–1599 and 812–785 cm1, respectively. The 1H NMR spectra showed signals ca. 8.60 (a), 9.35 (b) ppm and 7.55 (a), 8.79 (b) ppm for the NH and NHR protons, respectively. Reaction of a–b by any one of the three alternative methods described, i.e., potassium tetrachloropalladate in ethanol (method 1); lithium tetrachloropalladate in methanol (method 2); or palladium(II) acetate in glacial acetic acid (method 3), resulted in all cases in the tetranuclear species, [Pd{3FC6H3C(Me)@NN@C(S)NHR}]4 (R = Et 1a, R = Ph 1b), as air-stable solids, with the ligand in the E,Z configuration, which were fully characterized by microanalytical, mass spectra, IR and 1H NMR determinations (see Section 7). The mass spectrum (FAB) showed peaks at m/z 1375 (1a) and 1567 (1b) for the molecular ion whose isotopic composition suggests a tetranuclear complex of formula C44H48F4N12Pd4S4 (1a) and C60H48F4N12Pd4S4 (1b) (see Section 7). The m(C@N) band was shifted to lower wavenumbers upon complex formation by ca. 41 cm1 [27] indicating palladium coordination to the C@N moiety through the nitrogen lone pair [28,29]. The absence of the NH resonance in the 1H NMR spectra indicated deprotonation of the ANHA group [30,31], with loss of the C@S double bond character as confirmed by the absence of the m(C@S) band; this has been confirmed by the crystal structure resolution of complex 6a (vide infra). Metallation of the ligands was also made clear from the absence of the four proton spin system ABCD of the substituted phenyl ring; in the spectra of the complexes only three resonances were observed, inclusive of the coupling to the 19F nucleus, where appropriate, which were unambiguously assigned to the H2, H4 and H5 protons (see Section 7).

3. Reactivity of the complexes Treatment of 1a and 1b with the corresponding diphosphine dppm, dppe, dppp, dppb or trans-dppen [32] in 1:2 M ratio gave the dinuclear palladacycles [(Pd{3-FC6H3C(Me)@NN@C(S)NHR})2 (l-Ph2P(CH2)nPPh2)], (n = 1, 2a–b; 2, 3a–b; 3, 4a–b; 4, 5a–b), [(Pd {3-FC6H3C(Me)@NN@C(S)NHR})2(l-Ph2PCH@CHPPh2)], (6a–b), with a bridging phosphine ligand, as pure air-stable solids, which were fully characterized (see Scheme 1 and Section 7). The symmetric nature of the complexes was evident from the 1 H NMR spectra, which showed only one set of signals; consequently, only one singlet was observed in the 31P–{1H} spectra showing two equivalent phosphorus nuclei; with a chemical shift value pointing towards a phosphorus trans to nitrogen geometry [33–35]. The 1H NMR spectra showed the H5 resonance was coupled to the 31P nucleus and shifted to lower frequency between 0.9 and 1.4 ppm, suggesting a P trans to N arrangement [36]. Reaction of 1a–b with the short-bite diphosphine Ph2PCH2PPh2 (dppm) in 1:4 M ratio gave complexes [Pd{3-FC6H3C(Me)@NN@C (S)NHR}(Ph2PCH2PPh2-P)] 7a–b (Scheme 1), as pure air-stable compounds. Characteristic microanalytical and spectroscopic data are given in the Section 7. The mononuclear compounds showed

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cleavage of only the PdASbridging bond with coordination of the phosphine through only one phosphorus donor. In the 31P–{1H} spectra two doublets were assigned to the two non-equivalent phosphorus nuclei with the signal for the phosphorus nucleus bonded to the metal center at higher frequency. The proton part of the PCH2P ABXY spin system appeared as an apparent doublet ca. 3.3 ppm. Treatment of 7a–b with an equimolar amount of [PdCl2(PhCN)2] gave the homobimetallics [PdCl2{Pd[3-FC6H3C(Me)@NN@C(S) NHR](PPh2CH2PPh2)-P,S}], 8a–b, as pure air-stable solids, which were completely characterized (see Scheme 1 and Section 7). The analytical and spectroscopic data showed that the second metal was bonded via the phosphorus and sulfur atoms in a dimetallic six-membered chelate ring. Important spectroscopic features of 8a–b include two m(PdACl) bands in the IR spectra, with that trans to the phosphorus atom appearing at lower wavelengths, ca. 287 cm1, in agreement with the greater trans influence of the phosphorus atom, and the PdACl stretch trans to sulfur at ca. 326 cm1. The 31P NMR spectra showed the low-field shift of the terminal 31P resonance upon coordination to the metal, which was displaced by ca. 44 ppm, appearing at ca. 17 ppm, whilst the signal of the initially coordinated phosphorus atom shows a negligible shift. The resonance for the PCH2P protons, part of the PP0 HH0 system, appeared as an apparent triplet ca. 3.25 ppm, with an N value of 23 Hz (see the Section 7).

4. Structural studies: crystal structures of ligands a and b, and complex 6a Suitable crystals were grown by slowly evaporating chloroform/ n-hexane solutions. The crystal structures and the labelling schemes are shown in Figs. 1 and 2; crystal data are given in Table 1.

4.1. Crystal structures of 3-FC6H4C(Me)@NN(H)C(@S)NHEt (a) and 3-FC6H4C(Me)@NN(H)C(@S)NHPh (b)  space group Ligands a and b (Fig. 1) crystallize in the triclinic P1 as the E-isomer with respect to the N(1)AC(7) bond and Z with respect to the N(3)AC(8) bond. This arrangement is often found in thiosemicarbazones with at least one hydrogen attached to N (3) [38,39] due to weak N(3)AH(3)  N(1) hydrogen bonding. The C(8)AS(1), 1.622(16) Å (a) and 1.6733(17) Å (b), and the N(1)AC (7), 1.280(2) Å (a) and 1.284(2) Å (b), bond distances are consistent with a formal double bond character. The C(1)AC(7)AN(1) 115.86 (14)° (a), 115.50(14)° (b), and C(7)AN(1)AN(2) 119.44(14)° (a), 118.87(14)° (b), bond angles are in agreement with sp2 hybridization of the carbon and nitrogen atoms. The thioamide chain C(7)AN(1)AN(2)AC(8)AS(1)AN(3) is planar (rms = 0.0091 a and 0.0251 b) and at an angle of 9.83(9)° a, and 13.53(13)°, b with the fluorinated phenyl ring (rms = 0.0072, a and 0.0035, b). The parameters for the hydrogen bonding interaction in a (Fig. S1, SI) and b (Fig. S2, SI), are as follows: a, N(3)  N(1) 2.5957(19) Å, H (3 N)  N(1) 2.20 Å, N(3)AH(3 N)  N(1) 108.2°, N(2)  S(1)#1 3.627 Å, H(2 N)  S(1)#1 2.772 Å, N(2)AH(2 N)  S(1)#1 172.70°; S(1)  C(11)#1 3.437(2) Å, H(11C)#1  S(1) 2.62 Å, C(11)#1AH (11C)#1  S(1) 142.8°, with the symmetry operation #1[x, y, z]; and N(3)  F(1)#2 3.2416(18) Å, H(3 N)  F(1)#2 2.610 Å, N (3)AH(3 N)  F(1)#2 131.22°, with the symmetry operation #2 [x  1, y, z + 1]. The implication of the fluorine atom can explain the endo disposition of the ligand in the solid state; b, N (3)  N(1) 2.5878(19) Å, H(3)  N(1) 2.158 Å, N(3)AH(3)  N(1) 110.53°, N(2)  S(1)#1 3.7840 Å, H(2)  S(1)#1 2.925 Å, N(2)AH(2)  S(1)#1 176.32°; S(1)  C(15)#1 3.4690(19) Å,

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F

F

Ph2 P Pd N

Me

PPh2

Pd

v

S N

Ph 2 P

PPh2 N

Me

N

NHR 7a, 7b

Pd

S

Cl

Cl NHR

8a, 8b

iv RHN F 3 2

Me

N

4 5

S

F

6

i

F

ii

Ph2 P

Pd

N HN

N

Me

S

N

Me

N

NHR

NHR 1a, 1b

a: R = Et b: R = Ph

RHN

N

P Ph2

S N

N

Me

Pd

Pd Me

NHR

N

S Ph 2 P

F

2a: n = 1; 3a: n = 2; 4a: n =3; 5a: n = 4 2b: n = 1; 3b: n = 2; 4b: n =3; 5b: n = 4

iii

F

Pd nP Ph

S N

4

Me

2

Pd

S

N

F

NHR 6a, 6b

Scheme 1. (i) K2[PdCl4]/EtOH; LiCl/PdCl2/NaAcO/MeOH; Pd(AcO)2/AcOH, as appropriate; (ii) 1:2 Ph2P(CH2)nPPh2/acetone; (iii) trans-Ph2PCH@CHPPh2/acetone; (iv) 1:4 Ph2PCH2PPh2/ acetone; (v) [Pd(Cl)2(PhCN)2]/acetone.

a

b

Fig. 1. Molecular structure of ligands a and b with labelling scheme. Selected bond lengths (Å) and angles (°). (a) C(7)AN(1) 1.280(2), N(1)AN(2) 1.3735(18), N(2)AC(8) 1.359 (2), C(8)AS(1) 1.6822(16), C(8)AN(3) 1.324(2), C(1)AC(7)AN(1) 115.86(14), C(7)AN(1)AN(2) 119.44(14), N(1)AN(2)AC(8) 118.49(14), N(2)AC(8)AN(3) 116.05(14). (b) C(7)AN(1) 1.284(2), N(1)AN(2) 1.3724(19), N(2)AC(8) 1.362(2), C(8)AS(1) 1.6733(17), C(8)AN(3) 1.340(2), C(1)AC(7)AN(1) 115.50(14), C(7)AN(1)AN(2) 118.87(14), N(1)AN(2)AC(8) 118.79(14), N(2)AC(8)AN(3) 114.82(15).

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H(15C)#1  S(1) 2.75 Å, C(15)#1AH(15C)#1  S(1) 132.0°, with the symmetry operation #1[x, y + 1, z + 1]. 4.2. Crystal structure of [(Pd{3-FC6H3C(Me)@NN@C(S)NHEt})2 (l-PPh2CH@CHPPh2)] (6a)

Fig. 2. Molecular structure of complex 6a with labelling scheme. Selected bond lengths (Å) and angles (°) at palladium. Pd(1): Pd(1)AC(6) 2.00(2), Pd(1)AN(1) 2.041 (17), Pd(1)AP(1) 2.246(5), Pd(1)AS(1) 2.304(6), C(6)APd(1)AN(1) 79.4(8), C(6)APd (1)AP(1) 99.4(6), N(1)APd(1)AP(1) 178.4(5), C(6)APd(1)AS(1) 162.9(6), N(1)APd (1)AS(1) 83.5(6), P(1)APd(1)AS(1), 97.75(19), Pd(2): Pd(2)AC(43) 2.01(2), Pd(2)AN (4) 2.014(16), Pd(2)AP(2) 2.261(6), Pd(2)AS(2) 2.338(6), C(43)APd(2)AN(4) 81.0 (8), C(43)APd(2)AP(2) 97.6(7), N(4)APd(2)AP(2) 178.3(5), C(43)APd(2)AS(2) 164.6 (7), N(4)APd(2)AS(2) 83.6(6), P(2)APd(2)AS(2) 97.8(2).

In complex 6aCHCl3 the palladium atoms are bonded to four different donors, a tridentate thiosemicarbazone through the aryl C(6)/C(43) carbon, the imine N(1)/N(4) nitrogen, and the thioamide S(1)/(2) sulfur atom, and to a phosphorus atom P(1)/P(2) of transbis(diphenylphosphino)ethene, Fig. 2, in a slightly distorted square-planar coordination geometry, [Pd(1), C(6), N(1), S(1), P (1), plane 1] (rms = 0.0065 Å), and [Pd(2), C(43), N(4), S(2), P(2), plane 4] (rms = 0.0111 Å). The PdAC bond lengths, 2.00(2) and 2.01(2) Å, are shorter than the expected value of 2.081 Å [37], probably induced by partial multiple-bond character [38]. The angles between adjoining atoms in the coordination sphere are close to the theoretical value of 90°, with the most noteworthy strain in the CphenylAPdANazomethine angle 79.4(8) and 81.0(8)°, consequent upon chelation. The CAS, 1.78(2) and 1.79(2) Å, and CANhydrazynic, 1.31(2) and 1.33(2) Å] bond lengths show increased single and double bond character, respectively, consequent upon deprotonation of the hydrazynic group. All bond distances are within the expected range, with allowance for the strong trans influence of the phosphorus donor ligand, which is reflected in the Pd(1)AN(1) and Pd(2)AN(4) distances of 2.041(17) and 2.014 (16) Å, respectively (cf. sum of the covalent radii for palladium and nitrogen, 2.01 Å31). The palladium coordination plane is coplanar with the metallacycle and with the coordination ring, e.g., for [Pd(1), C(6), N(1), S(1),

Table 1 Crystallographic data and structure refinement data for ligands a, b and 6a. Compound

a

b

6aCHCl3

Empirical formula Formula weight Temperature Wavelength Crystal system Space group

C11H14FN3S 239.31 293(2) 1.54184 triclinic  P1

C15H14FN3S 287.35 293(2) 1.54184 triclinic  P1

C49H47Cl3F2N6P2Pd2S2 1203.14 293(2) 1.54184 monoclinic P2/c

5.7438(3) 8.3971(4) 13.0436(5) 96.011(4) 99.008(4) 106.893(5) 586.98(5) 2 1.354 2.380 252 0.48  0.24  0.08 3.47–74.94 7/h/7, 10/k/10, 16/l/0 2522 2411 [0.0428] 99.9% semi-empiric 0.8324 and 0.3946 full-matrix 2411/0/148 1.079 R1 = 0.0404, wR2 = 0.1189 R1 = 0.0491, wR2 = 0.1251 0.272 and 0.220

5.9710(2) 10.3994(4) 11.7755(5) 106.264(4) 90.305(5) 90.243(4) 701.91(5) 2 1.360 2.039 300 0.24  0.21  0.08 3.91–74.91 7/h/7, 0/k/13, 14/l/14 3056 2889 [0.0339] 99.9% semi-empiric 0.8504 and 0.6336 least-squares 2889/0/183 1.035 R1 = 0.0394, wR2 = 0.1061 R1 = 0.0560, wR2 = 0.1148 0.241 and 0.322

18.009(5) 11.620(4) 25.036(8) 90 98.501(6) 90 5182(3) 4 1.542 1.038 2424 0.36  0.24  0.20 1.14–21.96 18/h/18, 0/k/12, 0/l/26 6723 6723 [0.1452] 100.0% semi-empiric 0.8192 and 0.7062 on F2 6723/0/619 0.951 R1 = 0.0943, wR2 = 0.2258 R1 = 0.2039, wR2 = 0.2778 0.927 and 1.551

Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (Mg/m3) Absorption coefficient (mm1) F(0 0 0) Crystal size (mm3) h range for data collection (°) Index ranges Reflections collected Independent reflections [R(int)] Completeness to h Absorption correction Maximum and minimum transmission Refinement method Data/restraints/parameters Goodness-of-fit (GOF) Final R indices [I > 2r(I)] R indices (all data) Largest difference in peak and hole (e Å3)

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Fig. 3. Optimized structure for the ligand (R = CH2CH3) as obtained at the B3LYP/631G⁄ level of calculation.

P(1), plane 1], [Pd(1), C(6), C(1), C(7), N(1), plane 2] and [Pd(1), N (1), N(2), C(8), S(1), plane 3], respectively, with angles between planes: 1/2 = 1.04, 1/3 = 0.52, 2/3 = 0.77°; and for [Pd(2), C(43), N (4), S(2), P(2), plane 4], [Pd(2), C(43), C(38), C(44), N(4), plane 5] and [Pd(2), N(4), N(5), C(45), S(2), plane 6], respectively, with angles between planes: 4/5 = 0.76, 4/6 = 1.11, 5/6 = 1.19°. 5. Computational study DFT calculations were performed using the Gaussian g09 [39] package to obtain complementary information on the structural characteristics of the present species. This work analyses the rotation around the phosphine bridge and around the PAPd bond in order to rotate the thiosemicarbazone group. All reported geometries and frequency calculations were carried out at the B3LYP level of theory, using the standard basis set 6-31G⁄ for all non-metal atoms and the LANL2DZ basis set for palladium [40,41]. No imaginary frequencies were found. Due to computational costs, the systems were simplified in those parts not affecting the chemical characterization of the studied compounds herein. Thus, in a preoptimization stage all the phenyl groups present in phosphines were replaced by simpler methyl groups. After this previous study, all the species were fully optimized with the original phenyl groups. 5.1. Results In order to check the performance of the model the calculations carried out on ligands a and b, and on compound 6a were compared with the X-ray diffraction data, given certain deficiencies of the model such as the lack of solvent in the calculations. In all

Table 2 Selected distances and Wiberg bond orders obtained for the ligand at the B3LYP/6-31G⁄ level of calculations.

C7AN1 N1AN2 N2AC8 N2AH C8AN3 C8AS1 N3AC9 N3AH

B.O.

R (Å)

X-ray

1.688 1.124 1.118 0.766 1.259 1.478 0.953 0.758

1.295 1.353 1.385 1.015 1.343 1.679 1.452 1.013

1.280 1.374 1.359 1.324 1.682 1.456

cases, after comparing the results with those obtained from the crystallographic analysis it could be observed that the agreement was fairly acceptable confirming the goodness of the model. There are of course some differences such as slightly larger CAN distances, but in no case are they significant; the thiosemicarbazone chain is deviated ca. 25° from the ring plane. For instance, as shown in Table 2, for ligand a (Fig. 3), Wiberg bond orders as calculated from a Natural Bond Orbital Analysis correlate well with bond distances, clearly indicating the double or single character of the bonds. Therefore a double bond is clearly observed between C7AN1, whereas delocalization is observed for C8AS1 and C8AN3. In relation to the tetranuclear species 1 its structure was tested adopting the data from others previously obtained by us [18,26,42]; the structure is depicted in Fig. 4. Four ligand units are held together by the four palladium atoms which are bonded to nitrogen, carbon and two sulfur atoms in a square-planar arrangement at the metal center. The metallacycles and the phenyl rings are positioned so they can contribute via p-stacking to the stability of the system. In the process of studying the methylated derivative compounds four conformers were found upon rotating the PAPd bond (A–D). All have been studied at the B3LYP/6-31G⁄/LANL2DZ level. In 2a-met-A and 2a-met-B the torsion angle around the phosphine bridge allows the thiosemicarbazone planar groups to interact through p-stacking. In 2a-met-B the fluorinated phenyl rings are above each other whereas in 2a-met-A they occupy opposite positions relative to the phosphine (Fig. 5). Furthermore, structures 2amet-C and 2a-met-D are similar but in this case the torsion around the phosphine bridge sets the planar mutual groups apart; the most stable in each pair is shown in Fig. 7. Optimizations derived from these possibilities have been carried out leading to the minima shown in the Supplementary information. As may be observed in no case do the planar groups interact via p-stacking. Even in 2amet-A and 2a-met-B, where optimizations initiate with stacked structures the optimization procedure changes the torsion angles around the phosphine in order to avoid contact between the planar groups. Consequently the minima correspond to open structures where the planar groups do not interact significantly, halfway between fully stacked structures and open ones as in 2a-met-C and 2a-met-D. The most stable conformer is 2a-met-A and the less stable 2amet-C, with a relative energy of 3.67 kcal/mol; 2a-met-B is isoelectronic to 2a-met-A 0.17 kcal/mol; 2a-met-D is more stable than 2a-met-C, 1.79 kcal/mol. All energies were calculated in relation to the most stable 2a-met-A. In relation to the minima found for the other species considered in these calculations, there is nothing especially noteworthy except for the fact that in the case of 6a-met the presence of the C@C double bond forces the planar groups far apart, without any possibility of coming together. As for 7a-met and 8a-met they present the expected structure. Also, when the phosphine carbon chain contains two carbon atoms (3a-met) there is more flexibility and the open structure that avoids stacking (3a-met-D) is slightly favored by around 1 kcal/mol with respect to 3a-met-B; this is contrary to what is observed for species with an only-one carbon chain. After this preliminary analysis with the simplified systems calculations were carried out to include the phosphine phenyl groups. Thus, Fig. 6 shows two of the minima obtained for the 2a. As opposed to the results obtained for the simplified methylated systems in this case the structures clearly correspond to a stacked arrangement (2a-A) and to a second disposition without stacking between the planar groups (there is stacking with one planar group and with a phosphine phenyl ring, 2a-D). These results indicate that the stacked structure is less stable by 3.32 kcal/mol in agreement with previous results obtained for species with an ethyl

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Fig. 4. Optimized structure of the tetranuclear species 1a at the B3LYP/6-31G⁄/LANLD2Z level of calculations.

2a-met-A (0.00)

2a-met-B (0.17)

2a-met-C (3.67)

2a-met-D (1.79)

Fig. 5. The four conformers derivated from 2a-met and optimized at the B3LYP/6-31G⁄/LANL2DZ level.

bridge, where the crystal structure showed an arrangement similar to 2a-D. In this case the presence of the phenyl groups introduces extra steric hindrance in the crowded structure 2a-A resulting in a larger destabilization of the species. In relation to the remaining species shown in Fig. 7 it is noteworthy to point out that in the case of the 3a structures again the most stable minimum corresponds to 3a-D, as observed in the methylated derivatives. Following an overall view of the bond distance values and Wiberg bond orders presented in Table 3 it should be noted that the main electron rearrangement takes place when the tetranuclear species 1a is formed. In this case the C@S double bond

present in the ligand is broken after new PdAS bond formation; so, there is an elongation in the CAS bond from 1.679 to 1.807 Å, as well as rearrangement of other conjugated bonds. As for bond orders, there is a decrease from 1.478 to 1.028 in the CAS bond, together with changes from 1.118 to 1.526 in C8AN2 that acquires double bond character, the remaining bonds are not significantly altered. Upon formation of the tetranuclear complex the ligand bond distances undergo no further changes in the ensuing species, which show a very similar behavior to that described above. Only for compound 8a an increase in the CAS bond length was found (similar to 1a) due to double coordination of the sulfur atom (cf. C8AS1 1.822 Å, 8a, 1.77–1.78 Å in the rest of complexes).

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2a-A

2a-D

Fig. 6. Two different minima obtained for the 2a species at the B3LYP/6-31G⁄/LANL2DZ level.

3 a -D

6 a -A

7a

8a

Fig. 7. Most stable minima found for the rest of the species with phenyl groups considered in the calculation.

6. Conclusions Thiosemicarbazone tetranuclear palladacycles may be readily prepared in good yield by any one of three synthetic methods using either potassium tetrachloropalladate(II) in ethanol, lithium tetrachloropalladate(II) in methanol or palladium(II) acetate in glacial acetic acid. In all cases the organic moiety binds to palladium in

a tridentate [C,N,S] pincer fashion. Upon reaction with diphosphines only one PdAS bonds is cleaved which allows formation of dinuclear complexes or of mononuclear species that may behave as metalloligands; the latter are precursors for new bimetallics. DFT calculations have shown to be an adequate method to simulate and study the structures for those compounds where X-ray diffraction analysis was no possible.

J. Martínez et al. / Inorganica Chimica Acta 449 (2016) 20–30 Table 3 Distances (Å) and bond orders for the most stable conformations of the studied compounds with phenyl groups.

PdAC6 PdAS1 PdAN1 C8AS1 C8AN2 C8AN3 N1AN2 C7AN1 N3AC9 N3AH B.O. PdAC6 PdAS1 PdAN1 C8AS1 C8AN2 C8AN3 N1AN2 C7AN1 N3AC9 N3AH

Ligand

1a

2a

3a

6a

7a

8a

1.679 1.385 1.343 1.353 1.295 1.452 1.013

2.021 2.469 2.054 1.807 1.306 1.356 1.356 1.308 1.454 1.010

2.057 2.440 2.074 1.773 1.314 1.360 1.364 1.306 1.452 1.008

2.061 2.423 2.072 1.773 1.317 1.358 1.363 1.306 1.451 1.008

2.053 2.431 2.069 1.775 1.316 1.361 1.363 1.306 1.458 1.010

2.0574 2.4421 2.0732 1.7707 1.3156 1.3594 1.3628 1.3061 1.4508 1.0079

2.049 2.419 2.064 1.822 1.307 1.348 1.361 1.307 1.458 1.020

1.478 1.118 1.259 1.124 1.688 0.953 0.758

0.665 0.382 0.384 1.028 1.526 1.226 1.226 1.574 0.950 0.777

0.654 0.552 0.410 1.131 1.470 1.206 1.129 1.579 0.955 0.791

0.650 0.576 0.411 1.138 1.454 1.213 1.136 1.579 0.955 0.789

0.662 0.563 0.416 1.134 1.466 1.206 1.132 1.579 0.955 0.791

0.647 0.534 0.400 1.140 1.463 1.203 1.133 1.580 0.956 0.791

0.658 0.484 0.406 1.000 1.521 1.263 1.130 1.571 0.947 0.735

7. Experimental 7.1. General procedures Solvents were purified by standard methods [43]. Chemicals were reagent grade. Lithium tetrachloropalladate was prepared in situ by treatment of palladium(II) chloride with lithium chloride in methanol. Palladium(II) acetate and palladium(II) chloride were purchased from Alfa Products. The phosphines PPh2CH2PPh2 (dppm), PPh2(CH2)2PPh2 (dppe), trans-PPh2(CH@CH)PPh2 (dppen), PPh2(CH2)3PPh2 (dppp) and PPh2(CH2)4PPh2 (dppb) were purchased from Aldrich-Chemie. Microanalyses were carried out at the Servicio de Análisis Elemental at the Universidad de Santiago de Compostela using a Carlo Erba Elemental Analyzer Model EA1108. IR spectra were recorded as Nujol mulls or KBr discs with a Perkin-Elmer 1330, with an IR-FT Mattson Model Cygnus-100 and with a Bruker Model IFS-66V spectrophotometers. NMR spectra were obtained as CDCl3 solutions and referenced to SiMe4 (1H) or 85% H3PO4 (31P–{1H}) and were recorded with Bruker AMX 300, AMX 500 and WM 250 spectrometers. All chemical shifts are reported downfield from standards. The FAB mass spectra were recorded with a Fisons Quatro mass spectrometer with a Cs ion gun; 3-nitrobenzyl alcohol was used as the matrix. 7.2. Syntheses 7.2.1. Preparation of thiosemicarbazone 3-FC6H4C(Me)@NN(H)C(@S) NHEt (a) 30 -Fluoroacetophenone (1.159 g, 8.39 mmol) and hydrochloric acid (35%, 0.65 mL) were added to a suspension of 4-ethyl-3thiosemicarbazide (1.000 g, 8.39 mmol) in water (25 mL) to give a clear solution, which was stirred at room temperature for 4 h. The white solid that precipitated was filtered off, washed with cold water, and dried in air. Yield: 94%. Anal. Found: C, 55.3; H, 5.8; N, 17.8; S, 13.2; C11H14FN3S (239.3 g/mol) requires C, 55.2; H, 5.9; N, 17.6; S, 13.4%. IR (cm1): m(NAH) 3375s, 3233s; m(C = N) 1604m; m (C@S) 812m. 1H NMR (CDCl3/ppm): 8.60 (s, 1H, NH), 7.55 (br, 1H, NHEt), 7.43 (m, 2H, H2, H6), 7.37 (td, 1H, H5, 3JH5H4 = 8.3 Hz, 4 JH5F = 6.0 Hz), 7.10 (tdd, 1H, H4, 3JH4H5 = 8.3 Hz, 3JH4F = 8.3 Hz, 4 JH4H2 = 2.3 Hz), 3.78 (dq, 2H, NHCH2CH3, 3JHH = 7.4 Hz,

27

3

JH-NH = 5.5 Hz), 2.26 (s, 3H, CH3C@N), 1.32 (t, 3H, NHCH2CH3, JHH = 7.4 Hz). FAB-MS: m/z 240 [MH]+. Ligand b was synthesized following a similar procedure.

3

7.2.2. 3-FC6H4C(Me)@NN(H)C(@S)NHPh (b) Yield: >95%. Anal. Found: C, 62.8; H, 4.7; N, 14.5; S, 11.0; C15H14FN3S (287.4 g/mol) requires C, 62.7; H, 4.9; N, 14.6; S, 11.2%. IR (cm1): m(NAH) 3309s, 3254m; m(C@N) 1599m; m(C@S) 785m. 1H NMR (CDCl3/ppm): 9.35 (s, 1H, NH), 8.79 (s, 1H, NHPh), 7.44 (m, 3H, H2, H6, H5), 7.13 (tdd, 1H, H4, 3JH4H5 = 8.2 Hz, 3 JH4F = 8.2 Hz, 4JH4H2 = 2.5 Hz), 2.33 (s, 3H, CH3C@N). FAB-MS: m/z 288 [MH]+. 7.2.3 Preparation of [Pd{3-FC6H3C(Me)@NN@C(S)NHEt}]4 (1a) 7.2.3.1 Method 1. To a stirred solution of potassium tetrachloropalladate (0.200 g, 0.61 mmol) in water (6 mL) was added ethanol (40 mL). The fine yellow suspension of potassium tetrachloropalladate obtained was treated with 3-FC6H4C(Me)@NN(H)C(@S)NHEt (a) (0.161 g, 0.67 mmol, 10% excess). The mixture was stirred for 48 h at room temperature under nitrogen. The yellow precipitate was filtered off, washed with ethanol and dried. Yield: 95%. Anal. Found: C, 38.4; H, 3.7; N, 12.0; S, 9.2; C44H48F4N12Pd4S4 (1374.9 g/mol) requires C, 38.4; H, 3.5; N, 12.2; S, 9.3%. IR (cm1): m(NAH) 3423s, m(C@N) 1561m. 1H NMR (CDCl3/ppm): 7.37 (dd, 1H, H5, 3JH5H4 = 8.3 Hz, 4JH5F = 6.5 Hz), 6.68 (ddd, 1H, H4, 3JH4F = 9.7 Hz, 3JH4H5 = 8.3 Hz, 4JH4H2 = 2.8 Hz), 6.53 (dd, 1H, H2, 3JH2F = 10.2 Hz, 4JH2H4 = 2.8 Hz), 5.11 (t, 1H, NHEt, 3 JNH-H = 5.5 Hz), 3.42 (dq, 2H, NHCH2CH3, 3JHH = 7.4 Hz, 3JH-NH = 5.5 Hz), 1.76 (s, 3H, CH3C@N), 1.24 (t, 3H, NHCH2CH3, 3JHH = 7.4 Hz). FAB-MS: m/z 1375 [M]+. 7.2.3.2 Method 2. Ligand a (0.283 g, 1.18 mmol, 5% excess) and sodium acetate (0.185 g, 2.26 mmol) were added to a stirred solution of palladium(II) chloride (0.200 g, 1.13 mmol) and lithium chloride (0.096 g, 2.26 mmol) in methanol (40 mL). The mixture was stirred for 48 h at room temperature under nitrogen. The yellow precipitate was filtered off, washed with methanol, and dried. Yield: 85%. 7.2.3.3 Method 3. Ligand a (0.224 g, 0.94 mmol, 5% excess) and palladium(II) acetate (0.200 g, 0.89 mmol) were added to glacial acetic acid (45 mL) to give a clear solution, which was heated to 60 °C under nitrogen for 24 h. After this had cooled to room temperature, the yellow precipitate was filtered off, washed with ethanol, and dried. Yield: 89%. Compound 1b was synthesized following a similar procedure. 7.2.4 [Pd{3-FC6H3C(Me)@NN@C(S)NHPh}]4 (1b) 7.2.4.1 Method 1. Yield: 95%. Anal. Found: C, 45.8; H, 2.9; N, 10.6; S, 8.0; C60H48F4N12Pd4S4 (1567.0 g/mol) requires C, 46.0; H, 3.1; N, 10.7; S, 8.2%. IR (cm1): m(NAH) 3405 m, m(C@N) 1560m. 1H NMR (CDCl3/ppm): 7.22 (dd, 1H, H5, 3JH5H4 = 8.3 Hz, 4JH5F = 6.5 Hz), 6.97 (s, 1H, NHPh), 6.70 (m, 1H, H4), 6.60 (dd, 1H, H2, 3JH2F = 10.2 Hz, 4JH2H4 = 2.3 Hz), 1.83 (s, 3H, CH3C@N). FAB-MS: m/z 1567 [M]+. 7.2.4.2 Method 2. Yield: 90%. 7.2.4.3 Method 3. Yield: 82%. 7.2.5 Preparation of [(Pd{3-FC6H3C(Me)@NN@C(S)NHEt})2(l-PPh2CH2 PPh2)] (2a) The diphosphine PPh2CH2PPh2 (0.017 g, 0.045 mmol) was added to a suspension of complex 1a (0.030 g, 0.022 mmol) in acetone (15 mL). The mixture was stirred for 4 h and the resulting yellow solid was filtered off and dried. Yield: 69%. Anal. Found: C, 52.5; H, 4.3; N, 7.9; S, 6.2; C47H46F2N6P2Pd2S2 (1071.8 g/mol)

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requires C, 52.7; H, 4.3; N, 7.8; S, 6.0%. IR (cm1): m(NAH) 3427m; m (C@N) 1566m. 1H NMR (CDCl3/ppm): 6.60 (dd, 1H, H2, 3 JH2F = 10.6 Hz, 4JH2H4 = 2.8 Hz), 6.00 (m, 2H, H4, H5), 4.83 (br, 1H, NHEt), 3.75 (t, 1H, PCH2P), 3.42 (dq, 2H, NHCH2CH3, 3JHH = 7.4 Hz, 3 JH-NH = 5.5 Hz), 2.27 (s, 3H, CH3C@N), 1.22 (t, 3H, NHCH2CH3, 3 JHH = 7.4 Hz). 31P–{1H} NMR (CDCl3/ppm): 24.2 (s). Compounds 2b, 3a–3b, 4a–4b, 5a–5b and 6a–6b: These were synthesized following a similar procedure. 7.2.6 [(Pd{3-FC6H3C(Me)@NN@C(S)NHPh})2(l-PPh2CH2PPh2)] (2b) Yield: 43%. Anal. Found: C, 56.3; H, 3.9; N, 7.2; S, 5.3; C55H46F2N6P2Pd2S2 (1167.9 g/mol) requires C, 56.6; H, 4.0; N, 7.2; S, 5.5%. IR (cm1): m(NAH) 3406m; m(C@N) 1564w. 1H NMR (CDCl3/ ppm): 6.73 (s, 1H, NHPh), 6.59 (dd, 1H, H2, 3JH2F = 10.6 Hz, 4 JH2H4 = 1.9 Hz), 5.98 (m, 1H, H4), 5.89 (m, 1H, H5), 3.77 (t, 1H, PCH2P), 2.23 (s, 3H, CH3C@N). 31P–{1H} NMR (CDCl3/ppm): 24.1 (s). 7.2.7 [(Pd{3-FC6H3C(Me)@NN@C(S)NHEt})2(l-PPh2(CH2)2PPh2)] (3a) Yield: 77%. Anal. Found: C, 52.8; H, 4.4; N, 7.6; S, 5.7; C48H48F2N6P2Pd2S2 (1085.9 g/mol) requires C, 53.1; H, 4.5; N, 7.7; S, 5.9%. IR (cm1): m(NAH) 3392m; m(C@N) 1566m. 1H NMR (CDCl3/ ppm): 6.78 (dd, 1H, H2, 3JH2F = 10.6 Hz, 4JH2H4 = 2.8 Hz), 6.20 (m, 2H, H4, H5), 4.82 (br, 1H, NHEt), 3.41 (dq, 2H, NHCH2CH3, 3 JHH = 7.4 Hz, 3JH-NH = 5.5 Hz), 2.81 (br, 2H, P(CH2)2P), 2.34 (s, 3H, CH3C@N), 1.19 (t, 3H, NHCH2CH3, 3JHH = 7.4 Hz). 31P–{1H} NMR (CDCl3/ppm): 32.3 (s). 7.2.8 [(Pd{3-FC6H3C(Me)@NN@C(S)NHPh})2(l-PPh2(CH2)2PPh2)] (3b) Yield: 58%. Anal. Found: C, 56.6; H, 3.9; N, 7.0; S, 5.2; C56H48F2N6P2Pd2S2 (1181.9 g/mol) requires C, 56.9; H, 4.1; N, 7.1; S, 5.4%. IR (cm1): m(NAH) 3418m; m(C@N) 1565w. 1H NMR (CDCl3/ ppm): 6.85 (br, 1H, H2), 6.73 (s, 1H, NHPh), 6.26 (m, 2H, H4, H5), 2.85 (br, 2H, P(CH2)2P), 2.46 (s, 3H, CH3C@N). 31P–{1H} NMR (CDCl3/ppm): 32.1 (s). 7.2.9 [(Pd{3-FC6H3C(Me)@NN@C(S)NHEt})2(l-PPh2(CH2)3PPh2)] (4a) Yield: 54%. Anal. Found: C, 53.3; H, 4.6; N, 7.5; S, 5.8; C49H50F2N6P2Pd2S2 (1099.9 g/mol) requires C, 53.5; H, 4.6; N, 7.6; S, 5.8%. IR (cm1): m(NAH) 3404m; m(C@N) 1566m. 1H NMR (CDCl3/ ppm): 6.75 (dd, 1H, H2, 3JH2F = 10.6 Hz, 4JH2H4 = 2.3 Hz), 6.22 (m, 2H, H4, H5), 4.85 (br, 1H, NHEt), 3.43 (dq, 2H, NHCH2CH3, 3 JHH = 7.4 Hz, 3JH-NH = 5.5 Hz), 2.58 (m, 2H, PCH2CH2CH2P), 2.32 (s, 3H, CH3C@N), 2.15 (br, 1H, PCH2CH2CH2P), 1.19 (t, 3H, NHCH2CH3, 3 JHH = 7.4 Hz). 31P–{1H} NMR (CDCl3/ppm): 27.3 (s). 7.2.10 [(Pd{3-FC6H3C(Me)@NN@C(S)NHPh})2(l-PPh2(CH2)3PPh2)] (4b) Yield: 57%. Anal. Found: C, 57.0; H, 4.2; N, 7.0; S, 5.2; C57H50F2N6P2Pd2S2 (1196.0 g/mol) requires C, 57.2; H, 4.2; N, 7.0; S, 5.4%. IR (cm1): m(NAH) 3407m; m(C@N) 1564m. 1H NMR (CDCl3/ ppm): 6.82 (dd, 1H, H2, 3JH2F = 10.2 Hz, 4JH2H4 = 2.3 Hz), 6.75 (s, 1H, NHPh), 6.28 (m, 2H, H4, H5), 2.59 (m, 2H, PCH2CH2CH2P), 2.42 (s, 3H, CH3C@N), 2.23 (br, 1H, PCH2CH2CH2P). 31P–{1H} NMR (CDCl3/ ppm): 27.3 (s). 7.2.11 [(Pd{3-FC6H3C(Me)@NN@C(S)NHEt})2(l-PPh2(CH2)4PPh2)] (5a) Yield: 40%. Anal. Found: C, 53.8; H, 4.6; N, 7.5; S, 5.6; C50H52F2N6P2Pd2S2 (1113.9 g/mol) requires C, 53.9; H, 4.7; N, 7.5; S, 5.8%. IR (cm1): m(NAH) 3398m; m(C@N) 1566m. 1H NMR (CDCl3/ ppm): 6.77 (dd, 1H, H2, 3JH2F = 10.6 Hz, 4JH2H4 = 1.9 Hz), 6.25 (m, 2H, H4, H5), 4.80 (br, 1H, NHEt), 3.40 (dq, 2H, NHCH2CH3, 3 JHH = 7.4 Hz, 3JH-NH = 5.5 Hz), 2.32 (s, 3H, CH3C@N), 2.28 (br, 2H, PCH2CH2CH2CH2P), 1.76 (br, 2H, PCH2CH2CH2CH2P), 1.17 (t, 3H, NHCH2CH3, 3JHH = 7.4 Hz). 31P–{1H} NMR (CDCl3/ppm): 29.2 (s).

7.2.12 [(Pd{3-FC6H3C(Me)@NN@C(S)NHPh})2(l-PPh2(CH2)4PPh2)] (5b) Yield: 79%. Anal. Found: C, 57.5; H, 4.2; N, 6.7; S, 5.2; C58H52F2N6P2Pd2S2 (1210.0 g/mol) requires C, 57.6; H, 4.3; N, 6.9; S, 5.3%. IR (cm1): m(NAH) 3408m; m(C@N) 1564w. 1H NMR (CDCl3/ ppm): 6.84 (dd, 1H, H2, 3JH2F = 10.2 Hz, 4JH2H4 = 2.3 Hz), 6.78 (s, 1H, NHPh), 6.30 (m, 2H, H4, H5), 2.44 (s, 3H, CH3C@N), 2.34 (br, 2H, PCH2CH2CH2CH2P), 1.83 (br, 2H, PCH2CH2CH2CH2P). 31P–{1H} NMR (CDCl3/ppm): 29.2 (s). 7.2.13 [(Pd{3-FC6H3C(Me)@NN@C(S)NHEt})2(l-PPh2CH@CHPPh2)] (6a) Yield: 76%. Anal. Found: C, 53.0; H, 4.1; N, 7.6; S, 5.8; C48H46F2N6P2Pd2S2 (1083.8 g/mol) requires C, 53.2; H, 4.3; N, 7.8; S, 5.9%. IR (cm1): m(NAH) 3386m; m(C@N) 1566m. 1H NMR (CDCl3/ ppm): 6.77 (dd, 1H, H2, 3JH2F = 10.6 Hz, 4JH2H4 = 2.8 Hz), 6.24 (m, 1H, H5), 6.02 (td, 1H, H4, 3JH4F = 8.8 Hz, 3JH4H5 = 8.8 Hz, 4 JH4H2 = 2.8 Hz), 4.75 (br, 1H, NHEt), 3.35 (dq, 2H, NHCH2CH3, 3 JHH = 7.4 Hz, 3JH-NH = 5.5 Hz), 2.33 (s, 3H, CH3C@N), 1.13 (t, 3H, NHCH2CH3, 3JHH = 7.4 Hz). 31P–{1H} NMR (CDCl3/ppm): 33.0 (s). 7.2.14 [(Pd{3-FC6H3C(Me)@NN@C(S)NHPh})2(l-PPh2CH@CHPPh2)] (6b) Yield: 77%. Anal. Found: C, 56.8; H, 3.7; N, 6.9; S, 5.3; C56H46F2N6P2Pd2S2 (1179.9 g/mol) requires C, 57.0; H, 3.9; N, 7.1; S, 5.4%. IR (cm1): m(NAH) 3419m; m(C@N) 1565w. 1H NMR (CDCl3/ ppm): 6.84 (dd, 1H, H2, 3JH2F = 10.2 Hz, 4JH2H4 = 2.8 Hz), 6.68 (s, 1H, NHPh), 6.29 (m, 1H, H5), 6.08 (td, 1H, H4, 3JH4F = 8.3 Hz, 3 JH4H5 = 8.3 Hz, 4JH4H2 = 2.8 Hz), 2.44 (s, 3H, CH3C@N). 31P–{1H} NMR (CDCl3/ppm): 33.0 (s). 7.2.15 Preparation of [Pd{3-FC6H3C(Me)@NN@C(S)NHEt} (PPh2CH2PPh2)] (7a) The diphosphine PPh2CH2PPh2 (0.057 g, 0.148 mmol) was added to a suspension of complex 1a (0.050 g, 0.036 mmol) in acetone (15 mL). The mixture was stirred for 4 h. The resulting yellow solid was filtered off and dried. Yield: 49%. Anal. Found: C, 59.5; H, 4.8; N, 5.7; S, 4.3; C36H34FN3P2PdS (728.1 g/mol) requires C, 59.4; H, 4.7; N, 5.8; S, 4.4%. IR (cm1): m(NAH) 3427m; m(C@N) 1566m. 1 H NMR (CDCl3/ppm): 6.68 (dd, 1H, H2, 3JH2F = 10.6 Hz, 4 JH2H4 = 2.8 Hz), 6.19 (td, 1H, H4, 3JH4F = 8.8 Hz, 3JH4H5 = 8.8 Hz, 4 JH4H2 = 2.8 Hz), 6.10 (m, 1H, H5), 4.76 (br, 1H, NHEt), 3.41 (m, 2H, NHCH2CH3), 3.26 (d, 2H, PCH2P, 2JHP = 9.2 Hz), 2.31 (s, 3H, CH3C@N), 1.19 (t, 3H, NHCH2CH3, 3JHH = 7.4 Hz). 31P–{1H} NMR (CDCl3/ppm): 25.0 (d, 1 P, PA, 2JPP = 75.1Hz), 26.4 (d, 1 P, PB, 2 JPP = 75.1Hz). Compound 7b was synthesized following a similar procedure. 7.2.16 [Pd{3-FC6H3C(Me)@NN@C(S)NHPh}(PPh2CH2PPh2)] (7b) Yield: 62%. Anal. Found: C, 62.1; H, 4.5; N, 5.2; S, 3.9; C40H34FN3P2PdS (776.2 g/mol) requires C, 61.9; H, 4.4; N, 5.4; S, 4.1%. IR (cm1): m(NAH) 3409w; m(C@N) 1563w. 1H NMR (CDCl3/ ppm): 6.78 (s, 1H, NHPh), 6.73 (dd, 1H, H2, 3JH2F = 10.6 Hz, 4 JH2H4 = 2.8 Hz), 6.23 (td, 1H, H4, 3JH4F = 8.3 Hz, 3JH4H5 = 8.3 Hz, 4 JH4H2 = 2.8 Hz), 6.13 (m, 1H, H5), 3.29 (d, 2H, PCH2P, 2JHP = 9.2 Hz), 2.38 (s, 3H, CH3C@N). 31P–{1H} NMR (CDCl3/ppm): 25.1 (d, 1 P, PA, 2 JPP = 75.1 Hz), 26.4 (d, 1 P, PB, 2JPP = 75.1 Hz). 7.2.17 Preparation of [PdCl2{Pd[3-FC6H3C(Me)@NN@C(S)NHEt] (PPh2CH2PPh2)-P,S}] (8a) To a suspension of complex 7a (0.030 g, 0.041 mmol) in acetone (15 mL) was added [PdCl2(PhCN)2] (0.016 g, 0.041 mmol), and the mixture was stirred for 4 h. The resulting yellow solid was filtered off and dried. Yield: 78%. Anal. Found: C, 47.6; H, 3.7; N, 4.5; S, 3.3; C36H34Cl2FN3P2Pd2S (905.4 g/mol) requires C, 47.8; H, 3.8; N, 4.6; S, 3.5%. IR (cm1): m(NAH) 3431m; m(C@N) 1574m; m(PdACl) 328,

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286. 1H NMR (CDCl3/ppm): 6.84 (dd, 1H, H2, 3JH2F = 10.5 Hz, 4 JH2H4 = 2.8 Hz), 6.26 (td, 1H, H4, 3JH4F = 8.8 Hz, 3JH4H5 = 8.8 Hz, 4 JH4H2 = 2.8 Hz), 6.17 (m, 1H, H5), 5.37 (br, 1H, NHEt), 3.52 (m, 2H, NHCH2CH3), 3.20 (d, 2H, PCH2P, 2JHP = 9.2 Hz), 2.47 (s, 3H, CH3C@N), 1.29 (t, 3H, NHCH2CH3, 3JHH = 7.4 Hz). 31P–{1H} NMR (CDCl3/ppm): 23.0 (d, 1 P, PA, 2JPP = 75.1 Hz), 16.4 (d, 1 P, PB, 2 JPP = 75.1 Hz). Compound 8b was synthesized following a similar procedure. 7.2.18 [PdCl2{Pd[3-FC6H3C(Me)@NN@C(S)NHPh](PPh2CH2PPh2)-P,S}] (8b) Yield: 74%. Anal. Found: C, 50.2; H, 3.6; N, 4.3; S, 3.3; C40H34Cl2FN3P2Pd2S (953.5 g/mol) requires C, 50.4; H, 3.6; N, 4.4; S, 3.4%. IR (cm1): m(NAH) 3433m; m(C@N) 1572m; m(PdACl) 327, 285. 1H NMR (CDCl3/ppm): 6.96 (s, 1H, NHPh), 6.90 (dd, 1H, H2, 3 JH2F = 10.5 Hz, 4JH2H4 = 2.8 Hz), 6.40 (td, 1H, H4, 3JH4F = 8.3 Hz, 3 JH4H5 = 8.3 Hz, 4JH4H2 = 2.8 Hz), 6.20 (m, 1H, H5), 3.23 (d, 2H, PCH2P, 2JHP = 9.2 Hz), 2.54 (s, 3H, CH3C@N). 31P–{1H} NMR (CDCl3/ ppm): 23.0 (d, 1 P, PA, 2JPP = 75.1 Hz), 16.4 (d, 1 P, PB, 2JPP = 75.1 Hz).

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ica.2016.03.044. References [1] [2] [3] [4] [5] [6] [7]

[8] [9] [10] [11] [12] [13] [14]

8. X-ray crystallographic study Crystals of ligand a and b, and the complex 6aCHCl3 were mounted on a glass fiber and transferred to the diffractometer. For a and b room temperature X-ray data were collected on a CAD4 Enraf Nonius diffractometer using graphite monochromated Cu Ka radiation by the omega/2-theta method. For the complex 6aCHCl3 three dimensional, room temperature X-ray data were collected with Bruker SMART CCD diffractometer by the omega scan method, using monochromated Mo-Ka radiation. All the measured reflections were corrected for Lorentz and polarization effects and for absorption by semiempirical methods based on symmetry-equivalent and repeated reflections [Tmax/Tmin = 0.8324/0.3946 (a), 0.8504/0.6336 (b) and 0.8192/0.7062 (6a)]. The structures were solved by direct methods and refined by full matrix least squares on F2. Hydrogen atoms were included in calculated positions and refined in riding mode. Refinement converged at a final R = 0.0404 (a), 0.0394 (b) and 0.0943 (6a) (observed data, F), and wR2 = 0.1251 (a), 0.1148 (b) and 0.2778 (6a) (all unique data, F2), with allowance for thermal anisotropy of all non-hydrogen atoms. Minimum and maximum final electron densities: 0.220 and 0.272 (a), 0.322 and 0.241 (b) and 1.551 and 0.927 e Å3 (6a). Some atoms have rather large ADP values, however, it was not possible to lower these further most surely due to the quality of the crystals. Attempts to grow better crystals were not successful. The structure solutions and refinements were carried out with the SHELX-97 [44] program package. Acknowledgments The authors thank the Dirección de Investigación de la Universidad de Concepción, Chile VRID no. 214.021.033-1.0, and Project REDOC-UCO 1202 (Chile) and the Xunta de Galicia (Galicia, Spain), GRC2015/009 for financial support. Appendix A. Supplementary material Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the CCDC and 1431566 (a), 1431567 (b) and 1431565 (6a) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

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