Synthesis of diorganoplatinum(IV) complexes by the SS bond cleavage with platinum(II) complexes

Journal of Molecular Structure 1125 (2016) 20e26

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Synthesis of diorganoplatinum(IV) complexes by the SeS bond cleavage with platinum(II) complexes Fatemeh Niroomand Hosseini a, *, Mehdi Rashidi b, S. Masoud Nabavizadeh b a b

Department of Chemistry, Shiraz Branch, Islamic Azad University, Shiraz, 71993e37635, Iran Department of Chemistry, Shiraz University, Shiraz, 71467-13565, Iran

a r t i c l e i n f o

a b s t r a c t

Article history: Received 3 February 2016 Received in revised form 8 June 2016 Accepted 20 June 2016 Available online 21 June 2016

Reaction of [PtR2(NN)] (R ¼ Me, p-MeC6H4 or p-MeOC6H4; NN ¼ 2,20 bipyridine, 4,40 dimethyl2,20 bipyridine, 1,10phenanthroline or 2,9dimethyl1,10phenanthroline) with MeSSMe gives the platinum(IV) complexes cis,trans[PtR2(SMe)2(NN)]. They are characterized by NMR spectroscopy and elemental analysis. The geometries and the nature of the frontier molecular orbitals of Pt(IV) complexes containing PteS bonds are studied by means of the density functional theory. © 2016 Elsevier B.V. All rights reserved.

Keywords: Organoplatinum Disulfide SeS bond cleavage Oxidative addition DFT calculation

1. Introduction Disulfides play an important role in transition metal based organic sulfur chemistry and biochemistry which can be activated by transition metal complexes [1e3]. These reagents constitute a large family of RSe ligands that have been used for synthesis of transition metal complexes. Transition metal complexes including ligands of the type RSe, where R is an organic group, are significant in catalysis [4,5], and in medicinal chemistry [6e8]. Due to reducing nature of the RS group, the related complexes in high oxidation states are rare. Thus, the few known stable platinum(IV) thiolates complexes have been reported [9e11]. Surprisingly, studies on the platinum complexes incorporating MeSSMe ligand have been relatively rare [12,13] and there are no reports on the molecular orbital analysis of thiolate complexes in organoplatinum(IV) chemistry. Since the first report of the anticancer properties of cisplatin and the subsequent introduction of this compound into the clinic, a large number of Pt(II) and Pt(IV) complexes have been synthesized and examined for their antitumor activities [14e19]. In this connection, carboxylation of kinetically inert

* Corresponding author. E-mail addresses: [email protected], (F. Niroomand Hosseini). http://dx.doi.org/10.1016/j.molstruc.2016.06.049 0022-2860/© 2016 Elsevier B.V. All rights reserved.

[email protected]

dihydroxoplatinum(IV) compounds with different reagents such as acid anhydrides and acyl chlorides to form bis(carboxylato)platinum(IV) complexes, which are useful antitumor agents, has been of increasing interest [20]. One way to synthesize the organoplatinum(IV) complexes is the oxidative addition reaction of organic substrates to electron rich Pt(II) complexes [21e23]. Furthermore, there has been a great interest in recent decades to investigate oxidative addition reactions as of the most popular types of organometallic reactions. We have also experimentally and theoretically studied the oxidative addition of different reagents to platinum(II) complexes resulting in the octahedral platinum(IV) complexes [24e34]. Continuing our interest in the use of oxidative addition reactions in the synthesis of new organometallic complexes, we have explored the formation of such complexes via oxidation of platinum(II) reagents by dimethyl disulfide. In fact, we report here the synthesis and characterization of Pt(IV) complexes [PtR2(SMe)2(NN)] (R ¼ Me, p-MeC6H4 or pMeOC6H4; NN ¼ 2,20 bipyridine (bpy), 4,40 dimethyl 2,20 bipyridine (dmbpy), 1,10phenanthroline (phen) or 2,9dimethyl1,10phenanthroline (dmphen)), and the nature of the frontier orbitals of organoplatinum(IV) complexes in the presence of SMe group has been studied with the density functional calculations.

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139.3 (s, C4), 150.0 (s, C6), 155.0 (s, C2); aromatic C atoms of pMeC6H4 ligands 145.5 (s, 1J(PtC) ¼ 670.9 Hz, C atoms directly attached to Pt), 128.5 (s, Co atoms), 133.7 (Cp atoms), 136.9 (Cm atoms).

2. Experimental 2.1. General remarks The 1H NMR spectra were recorded as CDCl3 solutions on a Bruker Avance DPX 250 MHz spectrometer and TMS was used as external reference. All the chemical shift and coupling constants are in ppm and Hz, respectively. Melting points were recorded on a Buchi 530 apparatus and are uncorrected. The microanalyses were performed using a Thermofinigan Flash EA-1112 CHNO rapid elemental analyzer. The known complexes, [Pt(p-MeC6H4)2(phen)], 1a [35], [Pt(p-MeC6H4)2(bpy)], 1b [36], [Pt(p-MeC6H4)2(dmbpy)], 1c [28], [PtMe2(dmbpy)], 1e [37], and [PtMe2(dmphen)], 1f [38], were prepared by literature methods. The complex [Pt(pMeOC6H4)2(dmbpy)], 1d, was prepared similarly using cis-[Pt(pMeOC6H4)2(SMe2)2] precursor [39] and 4,40 dimethyl2,20 bipyridine; yield 88%, mp 278  C (decomp.); Anal. Calcd for C26H26N2O2Pt: C, 52.6; H, 4.4; N, 4.7. Found: C, 52.5; H, 4.5; N, 4.9. 1H NMR data: d 3.77 (s, 6H, Me groups on p-MeOC6H4 ligands), 2.42 (s, 6H, Me groups on dmbpy); aromatic protons of dmbpy ligand 8.48 [d, 3J(H5H6) ¼ 5.60 Hz, 3J(PtH) ¼ 19.4 Hz, 2H, H6], 6.82 [d, 3J(H6H5) ¼ 5.60 Hz, 2H, H5], 7.85 (s, 2H, H3); aromatic protons of MeOC6H4 ligands 7.39 [d, 3J(PtH) ¼ 64.18 Hz, 3 J(HmHo) ¼ 6.82 Hz, 4H, Ho], 6.90 [d, 3J(HoHm) ¼ 6.82 Hz, 4H, Hm]. 2.2. Synthesis of platinum(IV) complexes containing SMe groups

2.2.3. [Pt(p-MeC6H4)2(dmbpy)(SMe)2], 2c Yield 92%, mp 234  C (decomp.). The reaction mixture was stirred for 5 days. Anal. Calcd for C28H32N2PtS2: C, 51.3; H, 4.9; N, 4.3. Found: C, 51.5; H, 4.6; N, 4.5. 1H NMR data: d 1.19 (s, 3 J(PtH) ¼ 35.79, 6H, SMe), 2.31 (s, 6H, Me groups on p-MeC6H4 ligands), 2.63 (s, 6H, Me groups on dmbpy), 6.87 [d, 3 J(HoHm) ¼ 7.78 Hz, 4H, Hm of p-MeC6H4], 7.38 [d, 3J(HmHo) ¼ 7.78, 3 J(PtHo) ¼ 44.94 Hz, 4H, Ho of p-MeC6H4], 8.73 [d, 3 J(H6H5) ¼ 5.70 Hz, 3J(PtH6) ¼ 11.47 Hz, 2H, H6 of dmbpy], 7.32 [d, 3 J(H5H6) ¼ 5.70 Hz, 2H, H5 of dmbpy], 8.11 [s, 2H, H3 of dmbpy]. 2.2.4. [Pt(p-MeOC6H4)2(dmbpy)(SMe)2], 2d Yield 95%, mp 240  C (decomp.). The reaction mixture was stirred for 6 days. Anal. Calcd for C28H32N2O2PtS2: C, 48.9; H, 4.7; N, 4.1. Found: C, 49.0; H, 4.4; N, 4.3. 1H NMR data: d 1.18 (s, 3 J(PtH) ¼ 35.85, 6H, SMe), 2.63 (s, 6H, Me groups on dmbpy), 3.80 (s, 6H, Me groups on p-MeOC6H4 ligands), 6.69 [d, 3 J(HoHm) ¼ 7.18 Hz, 4H, Hm of p-MeOC6H4], 7.43 [d, 3J(HmHo) ¼ 7.18, 3 J(PtHo) ¼ 42.82 Hz, 4H, Ho of p-MeOC6H4], 8.73 [d, 3 J(H6H5) ¼ 5.74 Hz, 3J(PtH6) ¼ 11.52 Hz, 2H, H6 of dmbpy], 7.38 [d, 3 J(H5H6) ¼ 5.74 Hz, 2H, H5 of dmbpy], 8.12 [s, 2H, H3 of dmbpy].

The NMR labeling for Pt(IV) complexes is as follow: 4 3

5

6 SMe R N 2 Pt R N SMe

2.2.1. [Pt(p-MeC6H4)2(phen)(SMe)2], 2a Excess of MeSSMe (0.5 mL, 11.25 M) was added to a solution of [Pt(p-MeC6H4)2(phen)] (20 mg) in acetone (15 mL). The reaction mixture was stirred at room temperature for 2 h. The yellow solution turned colorless after this period. The solvent was evaporated, and residue was washed with acetone and dried in a vacuum. Yield 93%, mp 290  C (decomp.). Anal. Calcd for C28H28N2PtS2: C, 51.6; H, 4.3; N, 4.3. Found: C, 51.7; H, 4.4; N, 4.3. 1H NMR data: d 1.02 (s, 3J(PtH) ¼ 36.31, 6H, SMe), 2.32 (s, 6H, Me groups on p-MeC6H4 ligands), 6.92 [d, 3J(HoHm) 7.90 Hz, 4H, Hm of p-MeC6H4 ligand], 7.44 [d, 3J(HmHo) ¼ 7.90, 3J(PtHo) ¼ 45.33 Hz, 4H, Ho of p-MeC6H4 ligand], 9.18 [d, 3J(H2H3) ¼ 5.13 Hz, 3J(PtH2) ¼ 9.93 Hz, 2H, H2 of phen], 7.89 [dd, 3J(H3H2) ¼ 5.13 Hz, 3J(H4H3) ¼ 8.17 Hz, 2H, H3 of phen], 8.55 [d, 3 J(H4H3) ¼ 8.17 Hz, 2H, H4 of phen], 8.08 (s, 2H, H5 of phen). The following complexes were made similarly by using the appropriate Pt(II) complex and MeSSMe. 2.2.2. [Pt(p-MeC6H4)2(bpy)(SMe)2], 2b Yield 95% mp 295  C (decomp.). Anal. Calcd for C26H28N2PtS2: C, 49.7; H, 4.5; N, 4.5. Found: C, 49.9; H, 4.5; N, 4.6. 1H NMR data: d 1.18 (s, 3J(PtH) ¼ 35.74, 6H, SMe), 2.30 (s, 6H, Me groups on p-MeC6H4 ligands), 6.88 [d, 3J(HoHm) ¼ 8.06 Hz, 4H, Hm of p-MeC6H4], 7.38 [d, 3 J(HmHo) ¼ 8.06, 3J(PtHo) ¼ 44.84 Hz, 4H, Ho of p-MeC6H4], 8.93 [d, 3 J(H6H5) ¼ 5.61 Hz, 3J(PtH6) ¼ 11.11 Hz, 2H, H6 of bpy], 7.57 [m, 3 J(H5H6) ¼ 5.61 Hz, 2H, H5 of bpy], 8.32 [m, 3J(H4H3) ¼ 7.98 Hz, 2H, H4 of bpy], 8.10 [d, 3J(H3H4) ¼ 7.98 Hz, 2H, H3 of bpy]. 13C NMR data: d 13.1 (s, Me groups on p-MeC6H4 ligands) 21.2 (s, C atoms of SMe groups); aromatic C atoms of bpy ligand 123.7 (s, C5), 126.6 (s, C5),

2.2.5. [Pt(Me)2(dmbpy)(SMe)2], 2e Yield 89%, mp 175  C (decomp.). Anal. Calcd for C16H24N2PtS2: C, 38.2; H, 4.8; N, 5.6. Found: C, 38.4; H, 4.7; N, 5.4. 1H NMR data: d 1.43 (s, 2J(PtH) ¼ 68.43, 6H, MePt), 1.45 (s, 3J(PtH) ¼ 37.54, 6H, SMe), 2.59 (s, 6H, Me groups on dmbpy), 8.72 [d, 3J(H6H5) ¼ 4.58 Hz, 3 J(PtH6) ¼ 12.78 Hz, 2H, H6 of dmbpy], 7.45 [d, 3J(H5H6) ¼ 4.58 Hz, 2H, H5 of dmbpy], 8.01 [s, 2H, H3 of dmbpy]. 13C NMR data: d 5.0 (s, 1 J(PtC) ¼ 627.7 Hz, MePt), 8.5 (s, 2J(PtC) ¼ 14.1 Hz, SMe groups), 20.7 (s, C atoms of Me of dmbpy); aromatic C atoms of dmbpy ligand 123.1 (s, 3J(PtC) ¼ 8.7 Hz, C3), 126.6 (s, 3J(PtC) ¼ 14.1 Hz, C5), 145.7 (s, 2J(PtC) ¼ 14.1, C6), 149.8 (s, C4), 153.3 (s, C2). SMe + MeSSMe

Pt N

R

N

R

N

Pt N

R

R SMe

R 1a 1b 1c 1d 1e 1f

R

N N

4-MeC6H4 4-MeC6H4 4-MeC6H4 4-MeOC6H4 Me Me

phen bpy dmbpy dmbpy dmbpy dmphen

2a 2b 2c 2d 2e 2f

N N

4-MeC6H4 4-MeC6H4 4-MeC6H4 4-MeOC6H4 Me Me

Me

Me

N

N

N

N

N

N

N

N

Me bpy

Me dmbpy

phen

dmphen

Scheme 1. Preparation of platinum(IV) complexes.

phen bpy dmbpy dmbpy dmbpy dmphen

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Fig. 1. 1H NMR spectrum of [Pt(Me)2(dmbpy)(SMe)2], 2e. Assignments are given on the spectrum.

Fig. 2.

13

C NMR spectrum of [Pt(Me)2(dmbpy)(SMe)2], 2e. Assignments are given on the spectrum.

2.2.6. [Pt(Me)2(dmphen)(SMe)2], 2f Yield 90%, mp 152  C (decomp.). Anal. Calcd for C18H24N2PtS2: C, 41.0; H, 4.6; N, 5.3. Found: C, 40.6; H, 4.3; N, 4.9. 1H NMR data: d 1.45 (s, 3J(PtH) ¼ 36.01, 6H, SMe), 1.70 (s, 2J(PtH) ¼ 73.95, 6H, MePt), 3.25 (s, 6H, Me groups on dmphen), 7.66 [d, 3J(H4H3) ¼ 8.32 Hz, 2H, H3 of dmphen], 8.27 [d, 3J(H4H3) ¼ 8.32 Hz, 2H, H4 of phen], 7.85 (s, 2H, H5 of dmphen). 2.3. Computational details Gaussian 03 was used [40] to fully optimize all the structures at

the B3LYP level of density functional theory. The effective core potential of Hay and Wadt with a double-x valence basis set (LANL2DZ) was chosen to describe Pt [41,42]. The 6-31G(d) basis set was used for other atoms [43]. A polarization function xf ¼ 0.993 for Pt was also added. To evaluate and ensure the optimized structures of the molecules, frequency calculations were carried out using analytical second derivatives. In all cases only real frequencies were obtained for the optimized structures. The NBO analyses were carried out on the stationary points using the NBO 3.1 program [44] as implemented in Gaussian 03 suite of program. The molecular diagrams were constructed using the Chemissian program [40].

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23

Fig. 3. DFT optimized structures of the platinum(IV) complexes and the energy differences (kJ mol1) between the cis,trans and the cis,cis isomers. The H atoms are omitted for more clarity.

Table 1 Selected calculated bond distances (Å) and angles (deg) for complexes 2a-2f.

Me S2 (R)C2 (R)C1

Pt S1

N2 N1

Me

PteS1 PteC1(R) PteN1 PteS2 PteC2(R) PteN2 C1(R)ePteC2(R) N1ePteN2 S1ePteS2 N1ePteS1 N2ePteS2 C1(R)ePteS1 C1(R)ePteN1

2a

2b

2c

2d

2e

2f

2.469 2.033 2.255 2.459 2.039 2.253 88.7 74.7 172.6 85.6 86.1 93.3 98.3

2.469 2.034 2.252 2.457 2.041 2.241 88.2 74.0 172.1 85.2 85.5 93.6 99.0

2.470 2.034 2.237 2.457 2.041 2.237 88.2 73.9 172.2 85.0 85.5 93.6 99.0

2.471 2.036 2.243 2.457 2.042 2.234 87.7 74.0 172.2 85.5 85.9 93.4 99.2

2.451 2.063 2.251 2.436 2.061 2.243 84.6 73.8 178.0 90.7 97.7 91.2 101.9

2.444 2.063 2.337 2.434 2.065 2.328 84.1 72.5 176.5 88.8 95.1 89.9 102.2

3. Results and discussion 3.1. Synthesis and characterization of the organoplatinum(IV) complexes Dimethyl disulfide reacted cleanly with [PtR2(NN)] in acetone at room temperature to give Pt(IV) complexes with general formula of cis,trans-[PtR2(NN)(SMe)2] which could be isolated as an air stable yellow solid. The reactions proceeds by trans oxidative addition of MeSeSMe bond to platinum(II) complexes to give platinum(IV)

Fig. 4. The geometry of complex 2f.

complexes as shown in Scheme 1. The 1H NMR spectra of Pt(IV) complexes containing SMe groups are particularly informative. For example, for [PtMe2(dmbpy)(SMe)2], 2e, the 1H NMR spectrum (see Fig. 1) shows three groups of signals. At d ¼ 1.43 ppm, a 1:4:1 triplet is assigned to the Me groups directly connected to Pt center with 2J(PtH) ¼ 68.43 Hz. The terminal SMe hydrogens as a 1:4:1 triplet appear at d ¼ 1.45 with 3J(PtH) ¼ 37.54 Hz. The presence of only one signal due to MeePt and SMe indicates that the complex possesses a plane of symmetry as expected for a product of trans addition of dimethy

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F. Niroomand Hosseini et al. / Journal of Molecular Structure 1125 (2016) 20e26

Fig. 5. Qualitative frontier molecular orbitals for complexes 2a-2f.

F. Niroomand Hosseini et al. / Journal of Molecular Structure 1125 (2016) 20e26

disulfide. A signal at d ¼ 2.59 is assigned to methyl groups located on dmbpy ligand. The aromatic hydrogens related to dmbpy ligand appear at d 8.72 (with 3J(PtH6) ¼ 12.78 Hz), 8.01 and 7.45 for H6, H3 and H5, respectively. It is worthy to note that the 3J(PtH6) value of 12.78 Hz in this platinum(IV) complex is much lower than the corresponding value of 21.10 Hz for the starting platinum(II) complex, 1e. As is clear from Fig. 1, the H6 protons also appeared as only one doublet (with 3J(H6H5) ¼ 4.58 Hz) which further confirms the existence of a plane of symmetry. For this complex, the value of 2 J(PtH) is 68.43 Hz, which is lower than the corresponding value of 85.62 Hz for the starting platinum(II) complex [PtMe2(dmbpy)], 1e. Consistently, in the 13C NMR spectrum of 2e, in the Me region (see Fig. 2), a singlet with platinum satellites at d 0.5 with 1 J(PtC) ¼ 627.7 Hz was clearly assigned to two carbon atoms of methyl ligands, directly attached to Pt. A singlet appeared at d 8.5 with a 2J(PtC) value of 14.1 Hz for the SMe groups trans to each other. The methyl groups located on dmbpy ligand as a singlet signal observed at d ¼ 20.7. The presence of only one such signal for MePt, SMe and Me of dmbpy indicates the symmetrical stereochemistry of the complex as expected for the trans addition of MeSSMe. In the aromatic region, five different signals for the carbon atoms of the dmbpy ligand at d 123.1, 126.6, 145.7, 149.8 and 153.3 ppm were observed for C3 (with 3J(PtC) ¼ 8.7 Hz), C5 (with 3 J(PtC) ¼ 14.1 Hz), C6 (with 2J(PtC) ¼ 14.1 Hz), C4 and C2, respectively. The other organoplatinum(IV) complexes containing SMe ligand were characterized similarly (see the Experimental section). 3.2. Geometry optimization and frontier molecular orbitals The square-planar d8 complexes [PtR2(NN)] react with MeSSMe to give the Pt(IV) complexes with general formula cis,trans [PtR2(NN)(SMe)2] (see Scheme 1). As stated in the last section, the products of each reaction contained only the cis,trans isomers and no the cis,cis isomers were observed. This finding is in agreement with DFT calculations, showing that the cis-trans geometries were preferred over the corresponding cis,cis isomers as shown in Fig. 3. For example for complex [PtMe2(dmbpy)(SMe)2], 2e, our DFT calculations showed that the cis,cis isomer, is ruled out, because the energy for this isomer (SMe groups in a cis arrangement) is 27.4 kJ mol1 higher than that for cis,trans isomer, 2e. The possible geometries for complexes 2 were calculated theoretically. The calculated bond lengths and bond angles from DFToptimized structures at B3LYP level of theory are included in Table 1. A view of the DFT-optimized structures for these complexes is shown in Fig. 3. As can be seen from the optimized geometries, the SMe ligands occupy trans coordination sites and the methyl groups which are attached to sulfur atom lie above and below the bidentate NN ligand. The coordination geometry around platinum center of complexes 2a-2e contains two R (R ¼ methyl or aryl) groups, two nitrogen atoms of NN bidentate ligand and two SMe groups. As an example in the case of 2a, the bond distances between platinum and carbon atoms are 2.033 and 2.039 Å for PteC1 and PteC2, both trans to N, respectively. The para tolyl ligands are in a cis positioned with angle of 88.7, indicating that the angles around the Pt center are close to the ideal angle of 90 . The SMe groups are located trans to one another with the bond distances of PteS1 ¼ 2.469 and PteS2 ¼ 2.459 Å, respectively. The S1ePteS2 angle of 172.6 is close to linear arrangement. The aromatic N atoms are coordinated to platinum center, which is in accord to the usual preference of the phen ligand to act as chelating ligand and are positioned cis to SMe groups. The Me group bonded to S1 is oriented above the phen rings, while that located on S2 is oriented almost orthogonal to the first one.

25

The geometry of complex 2f containing 2,9-dimethyl-1,10phenanthroline ligand is shown in Fig. 4. It is worthy to note that the complex exhibits a major bowlike distortion which is indicated by the dihedral angle of 15.9 between the plane of the chelating moiety of the dmphen ligand (NeCeCeN) and the plane of coordination (CePteC). The PteN1 and PteN2 bond distances are longer than those observed for the complexes 2a-2e, in accord with the steric hindrance of methyl groups in positions of 2 and 9 of dmphen chelate ligand. The Me groups of dmphen ligand are displaced from phen plane, as indicated by the mean CeCeNeC torsion angle of 8.0 . Qualitative representations of the highest occupied and lowest unoccupied molecular orbitals in complexes 2a-2f are shown in Fig. 5. The energies of the relevant frontier orbitals of complexes 2a2f are also reported in Table 2. The HOMOeLUMO gap of 2a-2f ranges from 2.217 to 2.757 eV. The HOMO of complexes 2 is mainly orbitals of two SMe ligands with small contribution of Pt center (see Fig. 5). The LUMO of complexes 2 is essentially localized on the pp orbitals of NN chelating ligand.

4. Conclusion We have now extended the organoplatinum(IV) complexes containing SMe ligands and synthesized some unprecedented examples by the oxidative addition of MeSeSMe bond to platinum(II) center. Symmetrical cleavage of the SeS bond has been observed. This is a simple and useful route for preparation of complexes of general formula cis,trans[PtR2(SMe)2(NN)], where R ¼ Me, pMeC6H4 or p-MeOC6H4 and NN ¼ 2,20 bipyridine, 4,40 dimethyl2,20 bipyridine, 1,10phenanthroline or 2,9dimethyl1,10phenanthroline. The route to bis(thiolato) complexes is valuable since such platinum(IV) complexes may be important in catalysis [4,5] or medicinal chemistry [6,7]. The bis(thiolato)Pt(IV) products of the reaction of complex [PtR2(NN)] with MeSSMe contained only the thermodynamic isomers in which SMe groups are trans to each other, as was confirmed by DFT calculations. The sulfur-sulfur bond, along with other Group 16eGroup 16 bonds (e.g. OeO or RSeeSeR), should be considered as class A (nonpolar or of low polarity) substrates in the oxidative addition reactions [24,45]. Although there are three distinct mechanisms that are proposed for the activation of class A reagents, including radical pathway, the mechanism of reactions of Pt(II) complexes with MeSSMe is tentatively suggested to proceed via a 3-centered mechanism. As an example, the oxidative addition of H2O2 to Pt(II) complexes, has been kinetically studied and a cis-concerted mechanism has been suggested [27].

Table 2 Energies (eV) and main compositions (%) of the relevant frontier orbitals of complexes 2a-f. Complex

Orbital

E (eV)

Composition Pt

SMe

NN

R

2a

HOMO LUMO HOMO LUMO HOMO LUMO HOMO LUMO HOMO LUMO HOMO LUMO

4.718 2.425 4.752 2.447 4.674 2.311 4.656 2.322 4.495 2.278 4.724 2.149

11 1 11 1 11 1 11 1 12 1 9 2

85 3 83 3 84 3 84 2 86 2 86 2

1 96 2 96 2 96 2 96 2 96 4 96

3 0 3 1 3 1 3 1 1 0 1 1

2b 2c 2d 2e 2f

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Acknowledgments Financial supports of the Islamic Azad University and Shiraz University, is acknowledged.

[25]

[26]

References [1] G.C. Fortman, T. Kegl, C.D. Hoff, Kinetic, thermodynamic, and mechanistic aspects of oxidative addition reactions of RE-ER (E¼ S, Se, Te) and transition metal complexes, Curr. Org. Chem. 12 (2008) 1279e1297. [2] P.K. Dutta, A.K. Asatkar, S.S. Zade, S. Panda, Oxidative addition of disulfide/ diselenide to group 10 metal (0) and in situ functionalization to form neutral thiasalen/selenasalen group 10 metal (II) complexes, Dalton Trans. 43 (2014) 1736e1743. [3] J.D. Wrixon, J.J. Hayward, O. Raza, J.M. Rawson, Oxidative addition chemistry of tetrathiocines: synthesis, structures and properties of group 10 dithiolate complexes, Dalton Trans. 43 (2014) 2134e2139. [4] H. Kuniyasu, K. Sugoh, M.S. Su, H. Kurosawa, The first evidence of insertion of isocyanide into a metal-sulfur bond: catalytic and stoichiometric behavior of isocyanide and thiolate ligands on palladium and platinum, J. Am. Chem. Soc. 119 (1997) 4669e4677. [5] T. Kondo, T.-a. Mitsudo, Metal-catalyzed carbon-sulfur bond formation, Chem. Rev. 100 (2000) 3205e3220. [6] U. Bierbach, T.W. Hambley, J.D. Roberts, N. Farrell, Oxidative addition of the dithiobis (formamidinium) cation to platinum (II) chloro ammine compounds: studies on structure, spectroscopic properties, reactivity, and cytotoxicity of a new class of platinum (IV) complexes exhibiting S-thiourea coordination, Inorg. Chem. 35 (1996) 4865e4872. [7] S. Fakih, V.P. Munk, M.A. Shipman, P.d.S. Murdoch, J.A. Parkinson, P.J. Sadler, Novel adducts of the anticancer drug oxaliplatin with glutathione and redox reactions with glutathione disulfide, Eur. J. Inorg. Chem. (2003) 1206e1214. [8] H. Wei, X. Wang, Q. Liu, Y. Mei, Y. Lu, Z. Guo, Disulfide bond cleavage induced by a platinum (II) methionine complex, Inorg. Chem. 44 (2005) 6077e6081. [9] D. Roundhill, G. Wilkinson, Comprehensive Coordination Chemistry, vol. 5, Pergamon, 1987, p. 351. [10] M.P. Brown, R.J. Puddephatt, C.E. Upton, Synthesis, fluxional behaviour, and oxidative-addition reactions of some m-alkylthio-diplatinum (II) complexes, J. Chem. Soc. Dalton Trans. (1976) 2490e2494. [11] J. Hux, R. Puddephatt, Photochemistry of mononuclear and binuclear tetramethylplatinum (IV) complexes: reactivity of an organometallic free radical, J. Organomet. Chem. 437 (1992) 251e263. [12] V.G. Albano, M. Monari, I. Orabona, A. Panunzi, G. Roviello, F. Ruffo, Synthesis and characterization of trigonal-bipyramidal platinum (II) olefin complexes with chalcogenide ligands in axial positions. X-ray molecular structures of [Pt(SMe)2(dmphen)(diphenyl fumarate)], its cationic dipositive derivative [Pt(SMe2)2(dmphen)(diphenyl fumarate)][BF4]2, and free diphenyl fumarate, Organometallics 22 (2003) 1223e1230. [13] K.-T. Aye, J.J. Vittal, R.J. Puddephatt, Oxidative addition of EeE bonds (E¼ Group 16 element) to platinum (II): a route to platinum (IV) thiolate and selenolate complexes, J. Chem. Soc. Dalton Trans. (1993) 1835e1839. [14] J.J. Wilson, S.J. Lippard, Synthetic methods for the preparation of platinum anticancer complexes, Chem. Rev. 114 (2014) 4470e4495. [15] T.C. Johnstone, K. Suntharalingam, S.J. Lippard, The next generation of platinum drugs: targeted Pt (II) agents, nanoparticle delivery, and Pt (IV) prodrugs, Chem. Rev. 116 (2016) 3436e3486. [16] M. Jamshidi, R. Yousefi, S.M. Nabavizadeh, M. Rashidi, M.G. Haghighi, A. Niazi, A.-A. Moosavi-Movahedi, Anticancer activity and DNA-binding properties of novel cationic Pt (II) complexes, Int. J. Biol. Macromol. 66 (2014) 86e96. [17] R. Yousefi, S. Aghevlian, F. Mokhtari, H. Samouei, M. Rashidi, S.M. Nabavizadeh, Z. Tavaf, Z. Pouryasin, A. Niazi, R. Faghihi, The anticancer activity and HSA binding properties of the structurally related platinum (II) complexes, Appl. Biochem. Biotech. 167 (2012) 861e872. [18] R. Mohammadi, R. Yousefi, M. Dadkhah Aseman, S. Masoud Nabavizadeh, M. Rashidi, DNA binding and anticancer activity of novel cyclometalated platinum (II) complexes, Anti-Cancer Agents Med. Chem. 15 (2015) 107e114. [19] Z. Pouryasin, R. Yousefi, S.M. Nabavizadeh, M. Rashidi, P. Hamidizadeh, M.M. Alavianmehr, A.A. Moosavi-Movahedi, Anticancer and DNA binding activities of platinum (IV) complexes; importance of leaving group departure rate, Appl. Biochem. Biotech. 172 (2014) 2604e2617. [20] S. Choi, C. Filotto, M. Bisanzo, S. Delaney, D. Lagasee, J.L. Whitworth, A. Jusko, C. Li, N.A. Wood, J. Willingham, Reduction and anticancer activity of platinum (IV) complexes, Inorg. Chem. 37 (1998) 2500e2504. [21] G.K. Anderson, Platinum-carbon s-bonded Complexes, Elsevier, Oxford, 1995. [22] A.J. Canty, H. Jin, B.W. Skelton, A.H. White, Oxidation of complexes by (O2CPh)2 and (ER)2 (E¼ S, Se), including structures of Pd (CH2CH2CH2CH2)(SePh)2(bpy) (bpy¼ 2,20 -Bipyridine) and MMe2(SePh)2(L2)(M¼ Pd, Pt; L2¼ bpy, 1, 10-Phenanthroline) and C-O and C-E bond formation at palladium (IV), Inorg. Chem. 37 (1998) 3975e3981. [23] J. Collman, L. Hegedus, J. Norton, R. Finke, Principles and Applications of Organotransition Metal, Principles and Applications of Organotransition Metal Chemistry, University Science Books, Mill Valley, CA., 1987. [24] M. Crespo, M. Martínez, S.M. Nabavizadeh, M. Rashidi, Kinetico-mechanistic

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

[36]

[37] [38]

[39]

[40]

[41]

[42] [43]

[44]

[45]

studies on C X (X¼ H, F, Cl, Br, I) bond activation reactions on organoplatinum (II) complexes, Coord. Chem. Rev. 279 (2014) 115e140. S.J. Hoseini, H. Nasrabadi, S.M. Nabavizadeh, M. Rashidi, R.J. Puddephatt, Reactivity and mechanism in the oxidative addition of allylic halides to a dimethylplatinum (II) complex, Organometallics 31 (2012) 2357e2366. S.M. Nabavizadeh, S.J. Hoseini, B.Z. Momeni, N. Shahabadi, M. Rashidi, A.H. Pakiari, K. Eskandari, Oxidative addition of n-alkyl halides to diimineedialkylplatinum (II) complexes: a closer look at the kinetic behaviors, Dalton Trans. (2008) 2414e2421. M. Rashidi, M. Nabavizadeh, R. Hakimelahi, S. Jamali, Kinetics and mechanism of cleavage of the oxygeneoxygen bond in hydrogen peroxide and dibenzoyl peroxide by arylplatinum (II) complexes, J. Chem. Soc. Dalton Trans. (2001) 3430e3434. M. Rashidi, S.M. Nabavizadeh, A. Akbari, S. Habibzadeh, Secondary kinetic deuterium isotope effects in the reaction of MeI with organoplatinum (II) complexes, Organometallics 24 (2005) 2528e2532. M. Rashidi, N. Shahabadi, S.M. Nabavizadeh, Organoplatinum (IV) tris-chelate complexes, each having a cyclic metallacarbonate ring: synthesis, characterization and kinetic studies of the formation, Dalton Trans. (2004) 619e622. S.M. Nabavizadeh, F. Niroomand Hosseini, N. Nejabat, Z. Parsa, Bismuthehalide oxidative addition and bismuthecarbon reductive elimination in platinum complexes containing chelating diphosphine ligands, Inorg. Chem. 52 (2013) 13480e13489. S.M. Nabavizadeh, E.S. Tabei, F.N. Hosseini, N. Keshavarz, S. Jamali, M. Rashidi, Diorganoplatinum (ii) complexes with chelating PN ligand 2-(diphenylphosphinoamino) pyridine; synthesis and kinetics of the reaction with MeI, New J. Chem. 34 (2010) 495e499. S.M. Nabavizadeh, H. Amini, M. Rashidi, K.R. Pellarin, M.S. McCready, B.F. Cooper, R.J. Puddephatt, The mechanism of oxidative addition of iodine to a dimethylplatinum (II) complex, J. Organomet. Chem. 713 (2012) 60e67. M.D. Aseman, M. Rashidi, S.M. Nabavizadeh, R.J. Puddephatt, Secondary kinetic isotope effects in oxidative addition of benzyl bromide to dimethylplatinum (II) complexes, Organometallics 32 (2013) 2593e2598. S.M. Nabavizadeh, M.D. Aseman, B. Ghaffari, M. Rashidi, F.N. Hosseini, G. Azimi, Kinetics and mechanism of oxidative addition of MeI to binuclear cycloplatinated complexes containing biphosphine bridges: effects of ligands, J. Organomet. Chem. 715 (2012) 73e81. S. Habibzadeh, M. Rashidi, S.M. Nabavizadeh, L. Mahmoodi, F.N. Hosseini, R.J. Puddephatt, Steric and solvent effects on the secondary kinetic a-deuterium isotope effects in the reaction of methyl iodide with organoplatinum (II) complexes: application of a second-order technique in measuring the rates of rapid processes, Organometallics 29 (2010) 82e88. M. Rashidi, M. Nabavizadeh, R. Hakimelahi, S. Jamali, Kinetics and mechanism of cleavage of the oxygeneoxygen bond in hydrogen peroxide and dibenzoyl peroxide by arylplatinum (ii) complexes, J. Chem. Soc. Dalton Trans. (2001) 3430e3434. S. Achar, V.J. Catalano, A search for the elusive red form in substituted Pt(II) bipyridine complexes, Polyhedron 16 (1997) 1555e1561. A. Klein, E.J.L. McInnes, W. Kaim, Organometallic platinum(ii) complexes of methyl-substituted phenanthrolines, J. Chem. Soc. Dalton Trans. (2002) 2371e2378. M. Rashidi, M. Hashemi, M. Khorasani-Motlagh, R.J. Puddephatt, Aryldiplatinum (II) complexes containing dimethyl sulfide and bis(diphenylphosphino) methane as bridging ligands, Organometallics 19 (2000) 2751e2755. M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A.S. Voth, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople, GAUSSIAN 03, Revision B03, Gaussian, Inc., Pittsburgh PA, 2003. P.J. Hay, W.R. Wadt, Ab initio effective core potentials for molecular calculations. Potentials for the transition metal atoms Sc to Hg, J. Chem. Phys. 82 (1985) 270e283. L.E. Roy, P.J. Hay, R.L. Martin, Revised basis sets for the LANL effective core potentials, J. Chem. Theory Comput. 4 (2008) 1029e1031. P. Hariharan, J. Pople, Self-consistent-field molecular orbital methods. XII. Further extension of Gaussian-type basis sets, Theor. Chim. Acta 28 (1973) 213e222. E. Glendening, A. Reed, J. Carpenter, F. Weinhold, NBO Version 3.1, as Implemented in Gaussian 03, Revision, D. 01, Gaussian, Inc., Wallingford, CT, 2004. J.P. Collman, L.S. Hegedus, J.R. Norton, R.A. Finke, Principles and Applications of Organotransition Metal Chemistry, second ed., University Science Books, Mill Valley, CA, 1987. Ch. 5.