Pyridine-2-thionate as a versatile ligand in Pd(II) and Pt(II) chemistry: the presence of three different co-ordination modes in [Pd₂(μ₂-S,N-C₅H₄SN)(μ₂-κ²S-C₅H₄SN)(μ₂-dppm)(S-C₅H₄SN)₂]

Abstract

Reactions of [MCl₂(L–L)], M = Pt, Pd; L–L = bis(diphenylphosphino)methane (dppm) or bis(diphenylphosphino)ethane (dppe), with NaC₅H₄SN in a 1 : 2 molar ratio lead to mononuclear species [M(S-C₅H₄SN)₂(P–P)], M = Pt; L–L = dppm (1) or dppe (2) and M = Pd; L–L = dppe (3), as well as to the dinuclear [Pd₂(μ₂-S,N-C₅H₄SN)(μ₂-κ²S-C₅H₄SN)(μ₂-dppm)(S-C₅H₄SN)₂] (4). In contrast, reaction of [MCl₂(dppm)] with NaC₅H₄SN in a 1 : 1 molar ratio leads to [Pd₂(μ₂-S,N-C₅H₄SN)₃(μ₂-dppm)]Cl (5) and trans-[Pt(S-C₅H₄SN)₂(PPh₂Me)₂] (6) respectively. The latter is formed in low yield by cleavage of the dppm ligand. The dinuclear derivatives 4 and 5 present an A-frame and lantern structure, respectively. The former showing three different co-ordination modes in the same molecule with a short Pd–Pd distance of 2.9583 (9) Å and the latter with three bridging S,N thionate ligands showing a shorter Pd–Pd distance of 2.7291 (13) Å. Both distances could be imposed by the bridging ligands or point to some sort of metal–metal interaction.

---

Introduction

Compounds containing heterocyclic thione and/or thionate groups linked to one or more metallic centres have been known for several decades. However, in the last decade they have provoked more interest^1–5 due to their wide range of applications. In general, the presence of metal thiolates in biological systems,^6–8 their application as fungicides,^8,9 as electric conductors^10,11 and in the pharmaceutical industry,^9,12–14 including the anticarcinogenic properties^15,16 of some complexes with platinum and gold, have been responsible for, among other aspects, raising the interest in heterocyclic thiones and thionates as a source of sulfur donor ligands. The co-ordination chemistry of heterocyclic thiones and their corresponding anions as ligands is very rich, combining a soft and hard end which can be interesting for catalytic applications. Therefore, terminal S-bonding or N-bonding, S-bridging, N,S-chelating, N,S-bridging, N,S-chelation-cum-S-bridging or N,S-bridging-cum-S-bridging modes are found in the literature.^1–5 Structural studies show that binuclear complexes containing bridging heterocyclic thionate ligands are the most represented. However, in contrast with the large number of complexes based on two bridging ligands that have been reported, there are only two examples of three bridging co-ordination modes to date, that is, [NaV(μ₂-κ²S,κN-C₅H₄SN)₃(S,N-C₅H₄SN)(thf)₂]¹⁷ and [Ru₂(μ₂-κ²S,κN-C₅H₄SN)₂(μ₂-S,N-C₅H₄SN)(S,N-C₅H₄SN)₂][CF₃SO₃],¹⁸ the latter being the only reported example of coexistence of three different co-ordination modes of pyridine-2-thionate in the same complex.

With regard to the chemistry of palladium and platinum mononuclear complexes with the general formula [M(C₅H₄SN)₂(L)₂] (M = Pd, Pt; L = PPh₃,^19,20 L₂ = dppe²¹), [MCl(C₅H₄SN)(PPh₃)], [M(C₅H₄SN)₂(PPh₃)] (M = Pd, Pt),¹⁹ [PdCl(C₅H₄SN)(PPh₃)₂]¹⁹ or [{PdCl(S,N)(PMe₃)}₂] (S,N = C₅H₄SN,²² C₄H₃N₂S, C₄(Me)H₂SN₂ and C₃H₂SN(Me)N²³) or [Pd(S,N)(L)₂][ClO₄]²⁴ with S,N = C₅H₄SN, C₄H₃SN₂, C₃H₃SN₂, C₃H₂SN₂CH₃, C₃H₂S₂N and L = PPh₃ or L₂ = dppe, were prepared. The procedures used are oxidative addition reaction of dipyridyl-2,2′-disulfide to [M(PPh₃)₄], metathesis replacement of chlorine from [Pd(μ-Cl)Cl(PPh₃)]₂, [MCl(C₅H₄SN)(PPh₃)] and [Pd(μ-Cl)Cl(PMe₃)]₂, and deprotonation of the corresponding thione through the μ-hydroxo anion of the precursor²⁴ [{Pd(μ-OH)₂(L)₂}₂][ClO₄]₂.

In this paper we describe the reactions of sodium pyridine-2-thionate with [MCl₂(L–L)] (M = Pd, Pt and L–L = dppm, dppe) in a 2 : 1 or 1 : 1 molar ratio showing different behaviours depending on the metal, ligand or reactive molar ratios. With dppe—independent of metal and conditions—only disubstituted [M(C₅H₄SN)₂(dppe)] (2, 3) complexes are obtained. However, with the dppm derivatives, complexes [Pd₂(C₅H₄SN)₄(dppm)] (4) and [Pd₂(C₅H₄SN)₃(dppm)]Cl (5), or [Pt(C₅H₄SN)₂(dppm)] (1) were obtained. The X-ray structures confirm the mononuclear nature of 1 and in the case of dinuclear complexes 4 and 5 show an A-frame structure for the former and a lantern structure for the latter. In addition complex 4 shows an unprecedented combination of three different modes of co-ordination of pyridine-2-thionate in the same complex.

Experimental

Chemicals

Pyridine-2-thione (C₅H₅SN) (Aldrich), Na (Aldrich), dppm, dppe or PPh₂Me (Aldrich) were used as received. Platinum and PdCl₂ were procured from INCOMETAL, S.A. Reagent grade diethyl ether, hexane or dichloromethane were dried using standard procedures and freshly distilled immediately before use. Absolute ethanol was deoxygenated with an N₂ purge. The complexes [PtCl₂(dppm)], [PtCl₂(dppe)], [PdCl₂(dppm)] and [PdCl₂(dppe)] were prepared by adding the appropriate diphosphine ligand to a solution of [PtCl₂(COD)] or [PdCl₂(NCPh)₂]. These two reagents were prepared by literature routes or slight variations thereof.²⁵ All starting manipulations were carried out under a nitrogen atmosphere using Schlenk line and syringe techniques.²⁶

Physical measurements

¹H and ³¹P NMR spectra were recorded on a Varian Unity 300 MHz or INOVA 400 MHz for ¹H, and 121.4 MHz or 161.9 MHz for ³¹P, in CDCl₃ or CD₂Cl₂ solutions; ¹H chemical shifts are quoted relative to tetramethylsilane (internal reference) and the ³¹P NMR chemical shifts to H₃PO₄ (external reference) or to an internal reference. IR spectra were recorded on a Perkin Elmer 843 (range 4000–200 cm⁻¹) and/or a Nicolet Impact 410 FTIR (range 4000–400 cm⁻¹) spectrophotometers using Nujol mulls between polyethylene sheets. Conductivity measurements were performed at 298 K using a Crison 522 conductimeter (c ≈ 5.10⁻⁴ M). The C, H, N and S analyses were performed with a LECO CHNS 932 microanalyser. Mass spectra were recorded on a VG Autospec, by LSIMS+ using nitrobenzyl alcohol as matrix. The X-ray intensity data were collected with an Enraf Nonius Kappa CCD detector or a Bruker-Smart CCD diffractometer with graphite-monochromated Mo-Kα (λ = 0.71073 Å).

Syntheses

Preparation of [Pt(S-C₅H₄SN)₂(dppm)] (1). NaC₅H₄SN (0.390 mmol)—prepared in situ from NaEtO 0.1 M (3.9 mL, 0.390 mmol) and C₅H₅SN (43.4 mg, 0.390 mmol) in absolute CH₃CH₂OH (20 mL)—was added to a suspension of [PtCl₂(dppm)] (127 mg, 0.195 mmol) in absolute CH₃CH₂OH (20 mL) under an inert atmosphere. A pale bright yellow solution was formed immediately and the white solid in suspension remained mixed with a pale yellow solid. After stirring for 24 h at room temperature, the solvent was removed partially to concentrate the suspension to ca. 5 mL. The solid was filtered off and dissolved in CH₂Cl₂ (10 mL). The yellow solution was then filtered and concentrated to ca. 2 mL under vacuum. Diethyl ether was added to precipitate the product followed by filtration, washing with diethyl ether and hexane to produce a pale yellow crystalline solid in 86% yield. X-Ray quality crystals were grown by slow diffusion of hexane into a CH₂Cl₂ solution of the complex. Anal. Calcd for C₃₅H₃₀PtN₂P₂S₂: C, 52.56; H, 3.78; N, 3.51; S, 8.00. Found: C, 52.40; H, 3.93; N, 3.43; S, 7.84%. Λ_M (Ω⁻¹ cm² mol⁻¹): 2.18. IR (Nujol mull, cm⁻¹): (C₅H₄SN) 1573 (vs), 1545 (s). ¹H NMR (δ, in CDCl₃): 7.84 (m, 8 H, Ph), 7.41 (d, ³J_H6–H5 = 7.15 Hz, 2 H, C₅H₄SN), 7.27 (m, 12 H, Ph), 7.09 (m, 2H, C₅H₄SN), 6.96 (t, ³J_H5–H4 = 6.88 Hz, 2H, C₅H₄SN), 6.31 (t, ³J_H–H = 6.80 Hz, 2H, C₅H₄SN), 4.33 (t, ²J_H–P = 14.7 Hz, 2H, –CH₂–, dppm). ¹H{³¹P} NMR (δ, in CDCl₃): 4.33 (s, ³J_H–Pt = 58.1 Hz, 2H, –CH₂–, dppm). ³¹P{¹H} NMR (δ, in CDCl₃): −49.8 (s, ¹J_P–Pt = 2780.1 Hz). MS-LSIMS+ (m/z): 689 [Pt(C₅H₄SN)(dppm)⁺, 100%].

Preparation of [Pt(S-C₅H₄SN)₂(dppe)] (2). NaC₅H₄SN (0.386 mmol)—prepared in situ from NaEtO 0.1 M (3.9 mL, 0.386 mmol) and C₅H₅SN (43.0 mg, 0.386 mmol) in absolute CH₃CH₂OH (20 mL)—was added to a suspension of [PtCl₂(dppe)] (128.5 mg, 0.193 mmol) in absolute CH₃CH₂OH (20 mL) under an inert atmosphere. A lemon yellow solution appeared immediately and slowly became totally clear. After stirring for 5 h at room temperature, the solution was concentrated to ca. 5 mL under vacuum and hexane was added (20 mL). The pale yellow solid precipitate was isolated by filtration and obtained in 75% yield. Anal. Calcd for C₃₆H₃₂PtN₂P₂S₂: C, 53.13; H, 3.96; N, 3.44; S, 7.88. Found: C, 52.83; H, 3.81; N, 3.59; S, 7.66%. Λ_M (Ω⁻¹ cm² mol⁻¹): 3.8. IR (Nujol mull, cm⁻¹): (C₅H₄SN) 1566 (vs), 1542 (vs). ¹H NMR (δ, in CDCl₃): 7.80 (m, 8H, Ph), 7.62 (d, ³J_H6–H5 = 4.87 Hz, 2H, C₅H₄SN), 7.32 (m, 12 H, Ph), 7.26 (d, ³J_H3–H4 = 10.96 Hz, 2H, C₅H₄SN), 6.84 (td, ³J_H4–H5 = 7.39 Hz, ⁴J_H4–H6 = 1.93 Hz, 2H, C₅H₄SN), 6.40 (t, ³J_H–H = 7.58 Hz, 2H, C₅H₄SN), 2.21 (d, ²J_H–P = 18.17 Hz, ³J_H–Pt = 47.1 Hz, 4H, –CH₂–, dppe). ³¹P{¹H} NMR (δ, in CDCl₃): 46.29 (s, ¹J_P–Pt = 2966.29 Hz). MS-LSIMS+ (m/z): 703 [Pt(C₅H₄SN)(dppe)⁺, 100%].

Preparation of [Pd(S-C₅H₄SN)₂(dppe)] (3). NaC₅H₄SN (0.610 mmol)—prepared in situ from NaEtO 0.1 M (6.1 mL, 0.610 mmol) and C₅H₅SN (67.8 mg, 0.610 mmol) in absolute ethanol (20 mL)—was added to a suspension of [PdCl₂(dppe)] (175.5 mg, 0.305 mmol) in absolute ethanol (20 mL) under an inert atmosphere. A white-yellow suspension in an orange solution was formed immediately. After stirring for 24 h at room temperature, the solvent was removed under vacuum to ca. 5 mL and the solid filtered off. The resulting gold-yellow solid was purified by re-crystallisation from dichloromethane–hexane and 3 was isolated in 83% yield. Anal. Calcd for C₃₆H₃₂PdN₂P₂S₂: C, 59.63; H, 4.45; N, 3.86; S, 8.84. Found: C, 59.42; H, 4.65; N, 3.95; S, 8.97%. Λ_M (Ω⁻¹ cm² mol⁻¹): 1.7. IR (Nujol mull, cm⁻¹): (C₅H₄SN) 1567 (vs), 1542 (vs). ¹H NMR (δ, in CDCl₃): 7.79 (m, 10H, Ph, –N–C–H–, C₅H₄SN), 7.36 (m, 12H, Ph), 7.07 (d, ³J_H3–H4 = 8.00 Hz, 2H, C₅H₄SN), 6.79 (t, ³J_H–H = 8.00 Hz, 2H, C₅H₄SN), 6.44 (t, ³J_H–H = 8.00 Hz, 2H, C₅H₄SN), 2.31 (d, ²J_H–P = 20.0 Hz, 4H, –CH₂–, dppe). ³¹P{¹H} NMR (δ, in CDCl₃): 57.7 (s). MS-LSIMS+ (m/z): 614 [Pd(C₅H₄SN)(dppe)⁺, 100%].

Preparation of [Pd₂(μ₂-S,N-C₅H₄SN)(μ₂-κ²S-C₅H₄SN)(μ₂-dppm)(S-C₅H₄SN)₂] (4). NaC₅H₄SN (0.390 mmol)—prepared in situ from NaEtO 0.1 M (3.9 mL, 0.390 mmol) and C₅H₅SN (43.4 mg, 0.390 mmol) in CH₃CH₂OH (20 mL)—was added to a suspension of [PdCl₂(dppm)] (127 mg, 0.195 mmol) in CH₃CH₂OH (20 mL) under an inert atmosphere. A clear orange solution appeared within 5 minutes and the resulting solution was stirred for 4 h. The solution was concentrated under vacuum to ca. 1 mL, dichloromethane (10 mL) was added and the solid residue filtered off. Concentration of the resulting solution to ca. 2 mL and addition of hexane (20 mL) led to 4 as an orange solid in 76% yield. X-Ray quality crystals were grown by slow diffusion of hexane into a CH₂Cl₂ solution of the complex. Anal. Calcd for C₄₅H₃₈Pd₂N₄P₂S₄: C, 52.08; H, 3.69; N, 5.39; S, 12.36. Found: C, 51.82; H, 3.65; N, 5.20; S, 12.00%. Λ_M (Ω⁻¹ cm² mol⁻¹): 2.8. IR (Nujol mull, cm⁻¹): (C₅H₄SN) 1587 (s), 1572 (vs), 1558 (m), 1542 (s). ¹H NMR (δ, in CDCl₃): 9.39 (m, 1H, C₅H₄SN), 8.66 (m, 1H, C₅H₄SN), 8.48 (m, 1H, C₅H₄SN), 8.44 (m, 1H, C₅H₄SN), 8.23 (m, 1H, C₅H₄SN), 7.88 (m, 8H, Ph), 7.70 (m, 2H, C₅H₄SN), 7.50 (m, 2H, C₅H₄SN), 7.33 (m, 12H, Ph), 7.05 (m, 1H, C₅H₄SN), 6.92 (m, 1H, C₅H₄SN), 6.85 (m, 2H, C₅H₄SN), 6.53 (m, 1H, C₅H₄SN), 6.04 (m, 2H, C₅H₄SN), 4.36 (dt, ²J_H–P = 11.6 Hz, 1H, –CH₂–, dppm), 4.21 (dt, ²J_H–P = 11.6 Hz, 1H, –CH₂–, dppm). ¹H{³¹P} NMR (δ, in CDCl₃): 4.40 (d, AB system, J_AB = 14.6 Hz, 1H, –CH₂–, dppm), 4.18 (d, AB system, J_AB = 14.6 Hz, 1H, –CH₂–, dppm). ³¹P{¹H} NMR (δ, in CDCl₃): 33.75 (d, ²J_P–P = 48.6 Hz), 29.15 (d, ²J_P–P = 48.6 Hz). MS-FAB (m/z): 600 [Pd(C₅H₄SN)(dppm)⁺, 20%], 928 [Pd₂(C₅H₄SN)₃(dppm)⁺, 60%].

Preparation of [Pd₂(μ₂-S,N-C₅H₄SN)₃(μ₂-dppm)]Cl (5). NaC₅H₄SN (0.463 mmol)—prepared in situ from NaEtO 0.1 M (4.6 mL, 0.463 mmol) and C₅H₅SN (51.4 mg, 0.463 mmol) in absolute CH₃CH₂OH (20 mL)—was added to a suspension of [PdCl₂(dppm)] (259.9 mg, 0.463 mmol) in absolute CH₃CH₂OH (20 mL) under an inert atmosphere. A clear red-orange solution appeared within 5 minutes and it was stirred for 6 h. The solution was concentrated under vacuum to ca. 1 mL, dichloromethane (10 mL) was added and the solid residue filtered off. Concentration of the resulting solution to ca. 2 mL and addition of hexane (20 mL) resulted in 5 as a red-orange solid in a 63% yield. X-Ray quality crystals were grown by slow diffusion of hexane into a CH₂Cl₂ solution of the complex giving the corresponding dichloromethane and water solvate of complex 5. Anal. Calcd for C₄₁H₃₈Pd₂N₃OP₂S₃Cl: C, 46.19; H, 3.59; N, 3.94; S, 9.02. Found: C, 45.93; H, 3.61; N, 3.76; S, 8.78%. Λ_M (Ω⁻¹ cm² mol⁻¹): acetone, 46.0. IR (Nujol mull, cm⁻¹): (C₅H₄SN) 1585 (s), 1543 (m). ¹H NMR (δ, in CDCl₃): 9.41 (d, ³J_H–H = 5.15 Hz, 1H, C₅H₄SN), 8.70 (d, ³J_H–H = 5.15 Hz, 1H, C₅H₄SN), 8.48 (t, ³J_H–H = 7.67 Hz, 2H, C₅H₄SN), 8.20 (d, ³J_H–H = 5.77 Hz, 1H, C₅H₄SN), 8.11 (m, 2H, C₅H₄SN), 7.65 (m, 8H, Ph), 7.43 (t, ³J_H–H = 8.06 Hz, 2H, C₅H₄SN), 7.09 (d, ³J_H–H = 7.86 Hz, 1H, C₅H₄SN), 6.93 (m, 12H, Ph), 6.58 (dd, ³J_H–H = 6.96 Hz, 2H, C₅H₄SN), 4.36 (dt, ²J_H–P = 11.8 Hz, 1H, –CH₂–, dppm), 4.21 (dt, ²J_H–P = 11.8 Hz, 1H, –CH₂–, dppm). ¹H{³¹P} NMR (δ, in CDCl₃): 4.34 (d, AB system, J_AB = 11.7 Hz, 1H, –CH₂–, dppm), 4.21 (d, AB system, J_AB = 11.7 Hz, 1H, –CH₂–, dppm). ³¹P{¹H} NMR (δ, in CDCl₃): 32.85 (d, ²J_P–P = 60.8 Hz), 28.82 (d, ²J_P–P = 60.8 Hz). MS-LSIMS+ (m/z): 490 [Pd(dppm)⁺, 8%], 600 [Pd(C₅H₄SN)(dppm)⁺, 40%], 708 [Pd₂(C₅H₄SN)(dppm)⁺, 4%], 818 [Pd₂(C₅H₄SN)₂(dppm)⁺, 8%], 928 [Pd₂(C₅H₄SN)₃(dppm)⁺, 21%].

Preparation of trans-[Pt(S-C₅H₄SN)₂(PPh₂Me)₂] (6).
Method 1. Starting from NaC₅H₄SN (0.331 mmol)—prepared in situ from NaEtO 0.1 M (3.3 mL, 0.331 mmol) and C₅H₅SN (36.8 mg, 0.331 mmol) in absolute CH₃CH₂OH (20 mL)—and [PtCl₂(dppm)] (215.3 mg, 0.331 mmol) in absolute CH₃CH₂OH (20 mL) the reaction was carried out under the same conditions mentioned above for all cases. A pale bright yellow solution was formed immediately and the white suspended solid disappeared in half an hour. After stirring for 2 h at room temperature, the solvent was partially removed to concentrate the solution to ca. 5 mL. The pale yellow suspended solid was filtered off and dissolved in CH₂Cl₂ (10 mL). The pale yellow solution was then filtered and concentrated to ca. 2 mL under vacuum. Hexane (10 mL) was added to precipitate the product followed by filtration, washing with hexane to obtain a pale yellow crystalline solid in 40% yield. X-Ray quality crystals were grown by slow diffusion of hexane into a CH₂Cl₂ solution of the complex. Anal. Calcd for C₃₆H₃₄PtN₂P₂S₂: C, 53.00; H, 4.20; N, 3.43; S, 7.86. Found: C, 52.80; H, 4.13; N, 3.23; S, 7.64%. Λ_M (Ω⁻¹ cm² mol⁻¹): acetone, 3.2. IR (Nujol mull, cm⁻¹): (C₅H₄SN) 1572 (vs), 1541 (s). ¹H NMR (δ, in CD₂Cl₂): 7.96 (d, ³J_H6–H5 = 5.40 Hz, 2H, C₅H₄SN), 7.60 (m, 8H, Ph), 7.26 (m, 12H, Ph), 6.99 (d, ³J_H3–H4 = 8.05 Hz, 2H, C₅H₄SN), 6.87 (td, ³J_H–H = 7.0 Hz, ⁴J_H4–H6 = 1.83 Hz, 2H, C₅H₄SN), 6.63 (t, ³J_H5–H6 = 6.50 Hz, 2H, C₅H₄SN), 2.06 (t, ²J_H–P = 3.50 Hz, ³J_H–Pt = 24.8 Hz, 6H, –CH₃). ¹H{³¹P} NMR (δ, in CD₂Cl₂): 2.06 (s, ³J_H–Pt = 24.8 Hz, 6H, –CH₃). ³¹P{¹H} NMR (δ, in CD₂Cl₂): 8.28 (s, ¹J_P–Pt = 2733.3 Hz). MS-FAB+ (m/z): 505 [Pt(C₅H₄SN)(PPh₂Me)⁺, 33%], 705 [Pt(C₅H₄SN)(PPh₂Me)₂⁺, 100%].
Method 2. NaC₅H₄SN (40 mg, 0.300 mmol)—prepared in situ from NaEtO 0.1 M (3.0 mL, 0.300 mmol) and C₅H₅SN (33.3 mg, 0.300 mmol) in absolute CH₃CH₂OH (20 mL)—was added to a suspension of [PtCl₂(PPh₂Me)₂] (100.0 mg, 0.150 mmol) in absolute CH₃CH₂OH (20 mL) under an inert atmosphere. A pale bright yellow solution was formed and it became totally clear in 15 minutes. After stirring for 4 h at room temperature, the solution was concentrated to ca. 5 mL under vacuum and the pale yellow solid precipitate was isolated by filtration, washed with absolute ethanol (3 mL) and obtained in 82% yield. It was characterised by elemental analysis and ¹H and ³¹P NMR spectroscopies as compound 6.

X-Ray structure determinations of 1, 4, 5 and 6

Pale yellow (1), orange (4), red-orange (5) and yellow (6) crystals, suitable for X-ray diffraction, were grown by slow diffusion of hexane into a CH₂Cl₂ solution of each product at room temperature. A crystal of each compound was mounted on a glass fibre with inert oil and centred in a Enraf Nonius Kappa CCD area detector in the case of 1, or in a Bruker-Smart CCD diffractometer (4, 5 and 6) with graphite-monochromated Mo-Kα (λ = 0.7107 Å) radiation for data collection. Semi-empirical absorption corrections based on symmetry-equivalent reflections using SORTAV²⁷ were applied for 1. For structures 4, 5 and 6, the SADABS program was used to correct the absorption data.²⁸ A summary of the fundamental crystal and refinement data of the compounds is given in Table 1.

Table 1 Crystallographic data for 1, 4, 5 and 6

	1	4	5	6
a R1 = Σ|Fo| − |Fc|/Σ|Fo|. b wR2 = {Σw[|Fo|^2 − |Fc|^2]^2/Σw(Fo^2)^2}^1/2.
Empirical formula	C35H30N2P2PtS2	C45H38N4P2Pd2S4	C41H38Cl3N3OP2Pd2S3	C36H34N2P2PtS2
M	799.76	1037.77	1066.01	815.80
Crystal system	Orthorhombic	Monoclinic	Monoclinic	Monoclinic
Space group	P212121	P21/c	C2/c	P21/n
Z	4	4	8	2
a/Å	8.577(2)	20.508(4)	17.593(4)	8.8507(18)
b/Å	15.228(3)	9.0092(18)	16.091(3)	12.027(2)
c/Å	23.913(5)	25.545(5)	32.380(7)	15.874(3)
α/°	90.00	90.00	90.00	90.00
β/°	90.00	112.66(3)	93.58(3)	102.75(3)
γ/°	90.00	90.00	90.00	90.00
V/Å^3	3123.3(12)	4355.6(15)	9149(3)	1648.1(6)
ρ calcd/g cm^−3	1.701	1.583	1.548	1.644
Crystal dimensions/mm	0.3 × 0.25 × 0.25	0.55 × 0.40 × 0.30	0.40 × 0.25 × 0.35	0.15 × 0.10 × 0.10
T/K	150(2)	293(2)	293(2)	293(2)
No. of obsd data (I > 2σ(I))	7142	10779	4272	4084
R(int)	0.0616	0.0691	0.0463	0.0470
No. of parameters varied	379	516	502	197
μ/cm^−1	47.57	11.28	12.000	44.63
R1 (Fo)^a, wR2(Fo^2)^b (I > 2σ(I))	0.0277, 0.0632	0.0443, 0.0806	0.0515, 0.1532	0.0264, 0.0447
R1(Fo), wR2(Fo^2) (all data)	0.0308, 0.0647	0.0966, 0.0949	0.0633, 0.1607	0.0538, 0.0494

---

The structures were solved by direct methods using SHELXS.²⁹ Full-matrix least squares refinement was carried out using SHELXL minimizing w(F₀² − F_c²)².³⁰ Weighted R factors (R_w) and all goodness-of-fit S values are based on F²; conventional R factors (R) are based on F. In the case of 5 the dichloromethane molecule is disordered.

CCDC reference numbers 275126–275129.

For crystallographic data in CIF or other electronic format see DOI: 10.1039/b508438e

Results and discussion

The reaction of [PtCl₂(dppm)], [PtCl₂(dppe)] or [PdCl₂(dppe)] with an ethanolic solution of Na(C₅H₄SN) prepared in situ from equimolar amounts of C₅H₅SN and NaOEt in ethanol in a 1 : 2 molar ratio afforded complexes 1, 2 or 3, respectively, in good yields.

M = Pt L–L = dppm (

1

); dppe (

2

)

M = Pd L–L = dppe (

3

)

[MCl₂(L–L)] + 2 NaC₅H₄SN → [M(S–C₅H₄SN)₂(L–L)] + 2 NaCl (1)

The reaction pathway used by us can be considered as a slight modification of the one previously described²¹ to prepare compounds [Pt(S-C₅H₄SN)₂(dppe)] (2) or [Pd(S-C₅H₄SN)₂(dppe)] (3) starting from PtCl₄ or PdCl₂ and diphosphine ligand with C₅H₅SN and Et₃N as deprotonating agent. The spectroscopic data for 2 and 3 agree with those previously described²¹ for the mononuclear complexes although, in the case of complex 2, additional spectroscopic data are available in the Experimental section. Complex [Pt(S-C₅H₄SN)₂(dppm)] 1 shows a single resonance at δ = −49.8 ppm in the ³¹P{¹H} NMR spectrum in CDCl₃ which agree with a chelating behaviour of the diphosphine ligand.³¹ The presence of only a pair of platinum satellites, ¹J_P–Pt = 2780.1 Hz, point to a mononuclear structure of 1 similarly to those reported for complexes 2 and 3.

Crystals of 1 suitable for X-ray diffraction were grown by slow diffusion of hexane into a CH₂Cl₂ solution of the complex. An ORTEP representation of 1 is shown in Fig. 1 and selected bond distances and angles for the structure are given in Table 2. The molecular structure of 1 shows two pyridine-2-thionate ligands in a syn configuration with a dihedral angle of about 45° with the PtS₂P₂ plane. The geometry around the platinum atom can be considered distorted square-planar. The main distortion arises from the closing of the P(2)–Pt–P(1) and S(2)–Pt-S(1) angles [74.01(4)° and 78.56(4)° respectively], and the opening of the S(2)–Pt-P(2) and S(1)–Pt-P(1) angles [105.19(4)° and 102.25(4)° respectively] most likely imposed by the small bite angle of the bis(diphenylphosphino)methane ligand. The phenyl groups in the dppm ligand are in an up/down configuration on either side of the PtS₂P₂ plane, which precludes the presence of short Pt–Pt intramolecular interactions in the crystal lattice. Referenced structures of [Pt(S-C₅H₄SN)₂(dppx)] (dppx = dppe, dppn, dppp)²¹ and [Pt(S-C₅H₄SN)₂(bpy)]³² exhibit a difference in the orientation of the pyridine-2-thionate ligands. Pt–P distances of 2.2725(11) and 2.2702(11) Å are in the range of other mononuclear platinum derivatives with dppm as chelating ligand: [Pt(L)₂(dppm)] (L = CH₂Cl,³³ SePh,³⁴ SPh³⁵). The Pt–S bond distances are 2.3358(11) and 2.3381(11) Å, which are in the range of other Pt derivatives with terminal pyridine-2-thiolate ligands.^20,21,32 These P–Pt and Pt–S bond distances are similar to those found in compound 2; 2.270(3), 2.256(3) Å and 2.327(3), 2.389(3) Å respectively.²¹ The N–C–S angles of 120.7(3) and 120.8(3) in complex 1 are certainly close to the ideal angle for sp² carbons (trigonal angles) and are characteristic of a (S-C₅H₄SN) monodentate moiety.^20,36 These angles are 119.8(8)° and 114.7(9)° in compound 2 and 120.4(6)° and 114.7(6)° in compound 3.

Table 2 Bond lengths [Å] and angles [°] for [Pt(S-C₅H₄SN)₂(dppm)] (1)

Pt(1)–P(1)	2.2702(11)	N(1)–C(2)	1.336(5)
Pt(1)–P(2)	2.2725(11)	S(2)–C(2)	1.761(4)
Pt(1)–S(1)	2.3358(11)	S(1)–C(7)	1.748(4)
Pt(1)–S(2)	2.3381(11)	N(2)–C(7)	1.333(5)
P(1)–Pt(1)–P(2)	74.01(4)	C(1)–P(1)–Pt(1)	94.27(12)
P(1)–Pt(1)–S(1)	102.25(4)	C(21)–P(2)–Pt(1)	116.97(14)
P(2)–Pt(1)–S(1)	174.66(4)	C(31)–P(2)–Pt(1)	124.31(14)
P(1)–Pt(1)–S(2)	179.16(4)	C(1)–P(2)–Pt(1)	94.40(13)
P(2)–Pt(1)–S(2)	105.19(4)	C(7)–S(1)–Pt(1)	112.72(14)
S(1)–Pt(1)–S(2)	78.56(4)	C(2)–S(2)–Pt(1)	114.89(14)
C(51)–P(1)–Pt(1)	115.73(14)	S(2)–C(2)–N(1)	120.7(3)
C(41)–P(1)–Pt(1)	121.80(13)	S(1)–C(7)–N(2)	120.8(3)

---

Fig. 1 Molecular structure of complex 1. Thermal ellipsoids are drawn at the 50% probability level and H atoms have been omitted for clarity.

On the contrary, the reaction of [PdCl₂(dppm)] with thionate salts under similar conditions to those reported above shows a totally different result. Therefore, the final compound of this reaction (Scheme 1, i)) has a stoichiometry [Pd₂(C₅H₄SN)₄(dppm)] (4) deduced from elemental analyses, mass spectra (LSIMS+) and the integration of resonances in the ¹H NMR spectrum.

Scheme 1

Mass spectroscopy shows a signal assignable to the fragment [Pd₂(C₅H₄SN)₃(dppm)]⁺, m/z 928, 60% in accordance with the proposed stoichiometry by loss of one C₅H₄SN unit. The ³¹P{¹H} NMR spectrum shows two doublets at 33.75 and 29.15 ppm, ²J_P–P = 48.6 Hz, indicative of non-chelating dppm co-ordination and the non-equivalence of the two P ends. The ¹H NMR shows a complicated pattern in the phenyl region indicative of different modes of co-ordination of the thionate ligands and also an illustrative methylene resonance. The CH₂ protons appear as two doublets of triplets with some modifications of the intensities. ¹H{³¹P} NMR spectroscopy simplified these signals into an AB system, δ_A = 4.36, δ_B = 4.21, J_AB = 14.6 Hz which allows the measurement of J_H–P = 11.6 Hz in the original spectrum.

Fortunately crystals suitable for X-ray diffraction studies were grown. The structure of 4 (Fig. 2) displays a binuclear palladium A-frame derivative, where both metallic centres show a slightly distorted square-planar geometry. Selected bond distances and angles are given in Table 3. The molecule contains four pyridine-2-thionate ligands in 3 different co-ordination modes: two of them in a terminal S-monodentate arrangement, the other two as bridging ligands in two different modes. A μ₂-S,N and other μ₂-κ²S. This bridging combination has only been observed previously in the [{Rh(μ-C₅H₄SN)(tfbb)}₂] (tfbb = tetrafluorobenzobarrelene) dimer species³⁷ and three differing co-ordination modes in one compound has no precedent in the literature. The two pyridine-2-thionate groups in terminal position are trans to the S bridging atom, angles S(1)–Pd(2)–S(4) and S(2)–Pd(1)–S(4) being 173.16 (4)° and 178.08(4)° respectively. Both groups lie almost perpendicular to the Pd₂P₂NS plane, presumably in order to minimise repulsions between these rings and the phenyl rings of the dppm ligand. The Pd–Pd distance of 2.9584(9) Å is intermediate between that found for dimers such as [Pd₂Br₂(dppm)₂] 2.603 ų⁸ and [Pd₂(C₅H₄SN)₄]·2CHCl₃ 2.677(1) Å,³⁹ with a direct Pd–Pd bond in the former, and the distances in the A-frame lacking a direct Pd–Pd bond (range 3.01–3.3 Å).^40,41 The presence of three co-ordination modes allows us to underscore the different angles in monodentate S-pyridin-2-thionate N(1)–C(2)–S(1) 115.0(3)°, N(2)–C(7)–S(2) 119.2(3)°, μ₂-κ²S-bridging N(4)–C(17)–S(4) 116.1(3)° or μ₂-S,N-bridging N(3)–C(12)–S(3) 123.7(3)° compared with 120.6(1)° in pyridine-2-thione.³ Regarding the S–C distances they range from 1.742(4) to 1.790(4) Å. The shorter corresponds to μ₂-S,N co-ordination and the larger to the μ₂-κ²S co-ordination mode. This behaviour could be due to a larger electronic demand from the sulfur atom in the latter. The Pd(2)–N(3) distance of 2.098(3) Å is in the range of other similar compounds where the pyridine-2-thionate acts as chelating ligand.^22,39 However, the Pd–S and Pd–P bond lengths are slightly longer than those found in the above mentioned dimers and dppm A-frame derivatives.

Table 3 Bond lengths [Å] and angles [°] for [Pd₂(μ₂-S,N-C₅H₄SN)(μ₂-κ²S-C₅H₄SN)(μ₂-dppm)(S-C₅H₄SN)₂] (4)

Pd(1)–P(2)	2.2837(11)	Pd(2)–S(4)	2.3453(10)
Pd(1)–S(2)	2.3262(12)	S(1)–C(2)	1.754(4)
Pd(1)–S(3)	2.3515(11)	N(1)–C(2)	1.343(5)
Pd(1)–S(4)	2.3548(11)	S(2)–C(7)	1.741(5)
Pd(1)–Pd(2)	2.9584(9)	S(3)–C(12)	1.742(4)
Pd(2)–N(3)	2.098(3)	N(3)–C(12)	1.352(5)
Pd(2)–P(1)	2.2573(11)	S(4)–C(17)	1.790(4)
Pd(2)–S(1)	2.3361(11)	N(4)–C(17)	1.325(5)
P(2)–Pd(1)–S(2)	98.94(5)	S(4)–Pd(2)–Pd(1)	51.14(3)
P(2)–Pd(1)–S(3)	177.32(4)	C(28)–P(1)–Pd(2)	112.77(13)
S(2)–Pd(1)–S(3)	82.25(5)	C(22)–P(1)–Pd(2)	116.33(12)
P(2)–Pd(1)–S(4)	82.39(4)	C(1)–P(1)–Pd(2)	114.38(12)
S(2)–Pd(1)–S(4)	178.08(4)	C(34)–P(2)–Pd(1)	123.73(13)
S(3)–Pd(1)–S(4)	96.36(4)	C(40)–P(2)–Pd(1)	114.01(12)
P(2)–Pd(1)–Pd(2)	98.66(3)	C(1)–P(2)–Pd(1)	106.32(12)
S(2)–Pd(1)–Pd(2)	127.43(4)	C(2)–S(1)–Pd(2)	103.51(14)
S(3)–Pd(1)–Pd(2)	78.74(3)	C(7)–S(2)–Pd(1)	105.79(17)
S(4)–Pd(1)–Pd(2)	50.85(3)	C(17)–S(4)–Pd(2)	112.03(12)
N(3)–Pd(2)–P(1)	172.63(9)	C(17)–S(4)–Pd(1)	107.23(13)
N(3)–Pd(2)–S(1)	92.05(9)	Pd(2)–S(4)–Pd(1)	78.02(4)
P(1)–Pd(2)–S(1)	86.84(4)	C(12)–S(3)–Pd(1)	115.28(14)
N(3)–Pd(2)–S(4)	90.78(9)	C(16)–N(3)–Pd(2)	120.0(3)
P(1)–Pd(2)–S(4)	91.13(4)	C(12)–N(3)–Pd(2)	120.2(3)
S(1)–Pd(2)–S(4)	173.16(4)	N(1)–C(2)–S(1)	115.0(3)
N(3)–Pd(2)–Pd(1)	93.34(9)	N(2)–C(7)–S(2)	119.2(3)
P(1)–Pd(2)–Pd(1)	82.35(4)	N(3)–C(12)–S(3)	123.7(3)
S(1)–Pd(2)–Pd(1)	134.81(3)	N(4)–C(17)–S(4)	116.1(3)

---

Fig. 2 Molecular structure of complex 4. Thermal ellipsoids are drawn at the 50% probability level and H atoms have been omitted for clarity.

When the reaction is conducted in a 1 : 1 molar ratio (Scheme 1, ii) a different complex 5 can be obtained as the main component of the reaction, which can be re-crystallised from dichloromethane/hexane. The stoichiometry of complex 5 [Pd₂(C₅H₄SN)₃ (dppm)]Cl is similar to complex 4 with the replacement of one thionate group by a chlorine atom as evidenced by elemental analyses and the mass spectrum which shows fragments at [Pd₂(C₅H₄SN)₃(dppm)]⁺, m/z 928, 21%, [Pd₂(C₅H₄SN)₂(dppm)]⁺, m/z 818, 8% and [Pd₂(C₅H₄SN)(dppm)]⁺, m/z 708, 4% in accordance with the proposed stoichiometry by successive loss of Cl and C₅H₄SN units.

The ³¹P{¹H} NMR spectrum shows two doublets at 32.85 and 28.82 ppm, ²J_P–P = 60.8 Hz, characteristic of a non-symmetric bidentate bridging dppm ligand. Also, the ¹H NMR is very similar to the previous complex 4 except in the less complicated phenyl region and the intensity of the signals. The integration gives a dppm/thionate ratio of 1 : 3. The methylene region shows a doublet of doublets of triplets resolved into an AB system [¹H{³¹P} NMR, δ_A = 4.36, δ_B = 4.21, J_AB = 11.7 Hz] which allowed us to measure ²J_H–P = 11.8 Hz. This spectrum, which does not change substantially down to the lowest temperature (−55 °C) accessible in CDCl₃, points to a structure for complex 5 similar to those reported for complex 4. Only the conductivity in acetone (46 Ω⁻¹ cm² mol⁻¹), which is intermediate between non-conducting and 1 : 1 electrolyte, does not agree with this proposition. This is the reason why the X-ray structure of this complex was undertaken.

An ORTEP representation of the cationic species of 5 is shown in Fig. 3 and selected bond distances and angles for the structure are given in Table 4. The crystalline structure of the dichloromethane and water solvate of complex 5 consists of a chlorine salt where the cation is a dinuclear lantern-type palladium derivative with three pyridine-2-thionate ligands and one dppm acting as bridging ligands. Both palladium centres display a slightly distorted square-planar geometry. The two pyridine-2-thionate ligands in the equatorial position are sloping towards the third pyridine thionate (the one trans to the dppm ligand). The Pd–Pd distance (2.7288(12) Å) is comparable to that in [Pd₂(μ-C₅H₅NS)₄] (2.677(1) Å)³⁹ and [Pd₂(μ-bttz)₄] (2.745(1) Å)⁴² (bttz = 1,3-benzothiazole-2-thiolate), but significantly longer than those in [Pd₂(mhp)₄] (2.546(1)–2.559(3) Å)^43,44 (mhp = 6-methyl-2-hydroxypyridinate), [Pd₂(chp)₄] (2.567(2) Å) (chp = 6-chloro-2-hydroxypyridinate)⁴⁴ and [Pd₂(μ-dpb)₄] (2.576(1) Å)⁴⁵ (dpb = N,N′-diphenylbenzamidine) and slightly shorter than in palladium metal.⁴⁶ Again in this complex a short Pd–Pd distance is indicative of some metal–metal interaction and is probably imposed in this complex by the presence of the four bridging ligands. The Pd–S, Pd–N and Pd–P bond lengths are similar to those found in complex 4. The N–C–S angles of the μ₂-S,N pyridine-2-thionate ligands are 122.0(8)°, 123.4(6)° and 121.5(7)°, which are wider than in the other co-ordination modes of pyridine-2-thionate reported in this work. The N(2)–C(7)–S(2) angle of 123.4(6)° is close to the μ₂-S,N ligand in 4, 123.7(3)°, although does not correspond to the μ₂-S,N pyridine-2-thionate ligand trans to dppm.

Table 4 Bond lengths [Å] and angles [°] for [Pd₂(μ₂-S,N-C₅H₄SN)₃(μ₂-dppm)]Cl·CH₂Cl₂·H₂O (5)

Pd(1)–N(1)	2.081(8)	Pd(2)–P(2)	2.289(3)
Pd(1)–N(3)	2.128(7)	Pd(2)–S(1)	2.305(3)
Pd(1)–P(1)	2.266(3)	Pd(2)–S(3)	2.355(3)
Pd(1)–S(2)	2.296(2)	S(1)–C(2)	1.780(12)
Pd(1)–Pd(2)	2.7288(12)	S(2)–C(7)	1.762(9)
Pd(2)–N(2)	2.089(7)	S(3)–C(12)	1.768(11)
N(1)–Pd(1)–N(3)	92.3(3)	S(3)–Pd(2)–Pd(1)	86.34(7)
N(1)–Pd(1)–P(1)	94.0(2)	C(2)–S(1)–Pd(2)	107.4(4)
N(3)–Pd(1)–P(1)	173.2(2)	C(7)–S(2)–Pd(1)	105.5(3)
N(1)–Pd(1)–S(2)	175.1(3)	C(12)–S(3)–Pd(2)	104.0(3)
N(3)–Pd(1)–S(2)	88.6(2)	C(21)–P(1)–Pd(1)	113.4(3)
P(1)–Pd(1)–S(2)	85.33(9)	C(31)–P(1)–Pd(1)	114.1(4)
N(1)–Pd(1)–Pd(2)	90.5(2)	C(1)–P(1)–Pd(1)	114.1(3)
N(3)–Pd(1)–Pd(2)	87.8(2)	C(41)–P(2)–Pd(2)	114.5(4)
P(1)–Pd(1)–Pd(2)	94.82(7)	C(51)–P(2)–Pd(2)	115.8(3)
S(2)–Pd(1)–Pd(2)	84.81(7)	C(1)–P(2)–Pd(2)	111.2(3)
N(2)–Pd(2)–P(2)	94.4(2)	C(2)–N(1)–Pd(1)	122.8(7)
N(2)–Pd(2)–S(1)	175.9(2)	C(6)–N(1)–Pd(1)	118.7(7)
P(2)–Pd(2)–S(1)	86.52(10)	C(7)–N(2)–Pd(2)	120.8(6)
N(2)–Pd(2)–S(3)	89.5(2)	C(11)–N(2)–Pd(2)	119.9(6)
P(2)–Pd(2)–S(3)	176.10(9)	C(16)–N(3)–Pd(1)	116.0(7)
S(1)–Pd(2)–S(3)	89.61(10)	C(12)–N(3)–Pd(1)	124.5(6)
N(2)–Pd(2)–Pd(1)	90.3(2)	N(1)–C(2)–S(1)	122.0(8)
P(2)–Pd(2)–Pd(1)	93.83(7)	N(2)–C(7)–S(2)	123.4(6)
S(1)–Pd(2)–Pd(1)	85.56(7)	N(3)–C(12)–S(3)	121.5(7)

---

Fig. 3 The structure of the cation of complex 5. Thermal ellipsoids are drawn at the 50% probability level and H atoms have been omitted for clarity.

This different behaviour of [PdCl₂(dppm)] using a 1 : 1 or 1 : 2 NaC₅H₄SN molar ratio prompted us to test the reaction of [PtCl₂(dppm)] and [MCl₂(dppe)] (M = Pd, Pt) with a 1 : 1 molar ratio of NaC₅H₄SN. When [MCl₂(dppe)] (M = Pd, Pt) is used under these conditions only complexes 2 and 3 are obtained with some unreacted starting materials. However, the reaction of [PtCl₂(dppm)] with NaC₅H₄SN in a 1 : 1 molar ratio affords a small quantity of an insoluble derivative in ethanol, 6, which elemental analyses, mass spectra and NMR data surprisingly identify as [Pt(C₅H₄SN)₂(PPh₂Me)₂]. Complex 6 was obtained in 40% yield based on platinum. In the mother liquor of the reaction [Pt(C₅H₄SN)₂(dppm)] 1 can be identified as an important component among other phosphine containing materials, which in ours hands can not be separated.

Complex 6 shows a singlet at 8.28 ppm in the ³¹P{¹H} NMR in CD₂Cl₂ with only one set of platinum satellites, ¹J_P–Pt = 2733.3 Hz, which does not seem to belong to a dppm ligand. The ¹H NMR agrees with the presence of a thionate ligand and, what is even more remarkable, is the presence of a pseudo-triplet signal at 2.06 ppm, with small ²J_H–P = 3.5 Hz, that changes to a singlet with two satellites when the ¹H{³¹P} NMR spectrum was registered. The triplet at 2.06 ppm should correspond to the methyl groups of the two PPh₂Me ligands in trans positions, by virtual coupling. The LSIMS+ mass spectrum points in a similar direction showing fragments at m/z (%) 505 (33) and 705 (100) assignable to [Pt(C₅H₄SN)(PPh₂Me)]⁺, and [Pt(C₅H₄SN)(PPh₂Me)₂]⁺, respectively

The X-ray structure of one crystal of this compound has been resolved. An ORTEP representation of trans-[Pt(S-C₅H₄SN)₂(PPh₂Me)₂] (6) is shown in Fig. 4 and selected bond distances and angles for the structure are given in Table 5. The molecule consists of a centrosymmetric monomer with two methyl diphenyl phosphine molecules and two pyridine-2-thionate ligands, mutually trans. The metallic centre shows a slightly distorted square planar geometry. This structure is analogous to the previously reported trans-[Pt(C₅H₄NS)₂(PPh₃)₂]²⁰ although with an elongation in the Pt–P bond lengths, being 2.3149(11) Å in 6 and 2.295 and 2.253 Å in the reported derivative. In contrast, they are shorter than in the trans-[PdCl₂(PPh₂Me)₂]⁴⁷ distances Pd–P 2.3306 Å. It is not possible to compare 6 with the trans-dichlorobis(methyldiphenylphosphine)platinum(II) because only the cis isomer is referenced in the literature.⁴⁸ The Pt–S distances are in the range of platinum pyridin-2-thionate complexes.^20,21,32

Table 5 Bond lengths [Å] and angles [°] for trans-[Pt(S-C₅H₄SN)₂(PPh₂Me)₂] (6)

Symmetry transformations used to generate equivalent atoms: A −x + 2, −y, −z + 2.
Pt(1)–P(1)A	2.3149(11)	Pt(1)–S(1)	2.3435(9)
Pt(1)–P(1)	2.3149(11)	N(1)–C(1)	1.330(4)
Pt(1)–S(1)A	2.3435(9)	S(1)–C(1)	1.752(4)
P(1)A–Pt(1)–P(1)	180.00(5)	C(1)–S(1)–Pt(1)	106.50(12)
P(1)A–Pt(1)–S(1)A	85.12(3)	C(11)–P(1)–Pt(1)	111.08(11)
P(1)–Pt(1)–S(1)A	94.88(3)	C(6)–P(1)–Pt(1)	110.72(13)
P(1)A–Pt(1)–S(1)	94.88(3)	C(21)–P(1)–Pt(1)	121.24(11)
P(1)–Pt(1)–S(1)	85.12(3)	S(1)–C(1)–N(1)	120.3(2)
S(1)A–Pt(1)–S(1)	180.00(6)

---

Fig. 4 Molecular structure of complex 6. Thermal ellipsoids are drawn at the 50% probability level and H atoms have been omitted for clarity.

Complex trans-[Pt(S-C₅H₄SN)₂(PPh₂Me)₂] (6) can be obtained in higher yield (82%) by addition of NaC₅H₄SN in a 2 : 1 molar ratio, under an inert atmosphere, to a suspension of [PtCl₂(PPh₂Me)₂] in absolute ethanol. The complex obtained this way shows identical spectroscopic properties to those of the one described above, showing that the presence of the PPh₂Me ligand comes from a cleavage of the dppm ligand. There are a few references in the literature to P–C bond cleavage in platinum complexes containing bis(diphenylphosphino)methane. In some cases, the cleavage occurs under basic phase transference catalyst (PTC) conditions in which a dppm ligand is hydrolysed to produce PPh₂Me and other fragments,⁴⁹ and the formation of trans-[Pt₂(μ₂-OH)₂(POPh₂)₂(PPh₂Me)₂] from [PtCl₂(dppm)] are also referenced.⁵⁰ Other photochemical or thermal transformation of the dppm chelate ring have been reported.^51,52 We are currently doing some research work on this complex to understand the mechanism of this transformation, the first step of which could be the replacement of one chlorine atom with the pyridin-2-thionate ligand. Attempts to increase the yield of 6 by adding one free dppm to the reaction mixture failed giving similar results. Although in this case we were not able to isolate the other components of the reaction, essential to propose a mechanism; we are working with other heterocyclic thionate ligands to contribute more data to this reaction process.

Conclusions

In conclusion we have shown how the reactions of pyridine-2-thionate with [MCl₂(dppm)] (M = Pd or Pt) depend greatly on the ratio of thionate ligand used. In fact, with palladium we have shown here two rare examples of dinuclear complexes with three [Pd₂(μ₂-S,N-C₅H₄SN)₃(μ₂-dppm)]Cl (5) and four [Pd₂(μ₂-S,N-C₅H₄SN)(μ₂-κ²S-C₅H₄SN)(μ₂-dppm)(S-C₅H₄SN)₂] (4) thionate ligands in the molecule and, in the case of 4, the unprecedented existence of three different modes of co-ordination in the same molecule, that is: monodentate S-, μ₂-S,N and μ₂-κ²S. The comparison of the two structures with three and two thionate bridging ligands, respectively, shows how the Pd–Pd distance is modified from 2.7291(13) to 2.9583(9) Å, which should be imposed by the bridging μ₂-S,N ligands. In contrast, the chemistry of platinum derivative [PtCl₂(dppm)] affords mononuclear materials.

Acknowledgements

Financial support from MCyT-Spain-(BQU2002-04090-CO2-01 and BQU2002-00435) and JCyL-Spain-(BU15/03) is gratefully acknowledged. We thank Prof. M. B. Hurtshouse for the X-ray data collection involved in compound 1.

References

1. E. S. Raper, Coord. Chem. Rev., 1985, 61, 115.
2. E. S. Raper, Coord. Chem. Rev., 1994, 129, 91.
3. E. S. Raper, Coord. Chem. Rev., 1996, 153, 199.
4. E. S. Raper, Coord. Chem. Rev., 1997, 165, 475.
5. P. D. Akrivos, Coord. Chem. Rev., 2001, 213, 181.
6. P. J. Blower and J. R. Dilworth, Coord. Chem. Rev., 1987, 76, 121.
7. R. H. Holm, S. Ciurli and J. A. Weigel, Prog. Inorg. Chem., 1990, 38, 1.
8. J. G. Wright, M. J. Natan, F. M. McDonnell, D. M. Ralston and T. V. O'Halloran, Prog. Inorg. Chem., 1990, 38, 323.
9. K. C. Dash and H. Schmidbaur, Metal Ions in Biological Systems, Marcel Decker, New York, 1982, vol. 14, p. 179.
10. B. M. Sutton, Gold Bull. (Geneva), 1986, 19, 15.
11. M. J. Williams, Organic Superconductors (including Fullerenes) Synthesis, Structure, Properties and Theory, Prentice Hall, Englewood Cliffs, NJ, 1992.
12. P. J. Sadler, Adv. Inorg. Chem. Radiochem., 1991, 36, 1.
13. J. Burgess, Transition Met. Chem., 1993, 18, 439.
14. D. H. Brown and W. E. Smith, Chem. Soc. Rev., 1980, 9, 217.
15. J. Reedijk, Inorg. Chim. Acta, 1992, 200, 873.
16. M. J. Bloemink and J. Reedijk, in Metal Ions in Biological Systems, Marcel Dekker Inc, New York, 1996, vol. 32, p. 641.
17. J. G. Reynolds, S. C. Sendlinger, A. M. Murray, J. C. Huffman and G. Christou, Angew. Chem., Int. Ed. Engl., 1992, 31, 1253.
18. M. Sokolow, Y. Sasaki and K. Umakoshi, Inorg. Chem. Commun., 2001, 4, 142.
19. Y. Nakatsu, Y. Nakamura, K. Matsumoto and S. Ooi, Inorg. Chim. Acta, 1992, 196, 81.
20. T. S. Lobana, R. Verma and A. Castineiras, Polyhedron, 1998, 17, 3753.
21. T. S. Lobana, R. Verma, G. Hundal and A. Castineiras, Polyhedron, 2000, 19, 899.
22. J. H. Yamamoto, W. Yoshida and C. M. Jensen, Inorg. Chem., 1991, 30, 1353.
23. G. P. A. Yap and C. M. Jensen, Inorg. Chem., 1992, 31, 4823.
24. J. L. Serrano, J. Pérez, G. Sánchez, J. F. Martínez, G. López and E. Molins, Transition Met. Chem., 2002, 27, 105.
25. (a) D. Drew and J. R. Doyle, Inorg. Synth., 1990, 28, 346; (b) G. K. Anderson and M. Lin, Inorg. Synth., 1990, 28, 60.
26. D. F. Shriver and M. A. Drezdzon, The manipulation of Air-Sensitive Compounds, Wiley-Interscience, New York, 2nd edn, 1986.
27. G. M. Sheldrick, SHELXTL, University of Göttingen, Göttingen, Germany, 1997.
28. G. M. Sheldrick, SADABS, Empirical Absorption Program, University of Göttingen: Göttingen, Germany, 1996.
29. G. M. Sheldrick, SHELXS, Program for Crystal Structure Solution, University of Göttingen, Göttingen, Germany, 1990.
30. G. M. Sheldrick, SHELXL, Program for the refinement of crystal structures from diffraction data, University of Göttingen, Göttingen, Germany, 1997.
31. P. E. Garrou, Chem. Rev., 1981, 81, 229.
32. B. C. Tzeng, W. F. Fu, C. M. Che, H. Y. Chao, K. K. Cheung and S. M. Peng, J. Chem. Soc., Dalton Trans., 1999, 1017.
33. N. W. Alcock, P. G. Pringle, P. Bergamini, S. Sostero and O. Traverso, J. Chem. Soc., Dalton Trans., 1990, 1553.
34. V. K. Jain, S. Kannan, R. J. Butcher and J. P. Jasinski, J. Chem. Soc., Dalton Trans., 1993, 1509.
35. G. W. Wei, M. C. Hong, Z. Y. Huang and H. Q. Liu, Jiegou Huaxue, 1992, 11, 334.
36. S. Wang and J. P. Fackler, Jr., Inorg. Chem., 1989, 28, 2615.
37. M. A. Ciriano, F. Viguri, J. J. Pérez-Torrente, F. J. Lahoz, L. A. Oro, A. Tiripicchio and M. Tiripicchio Camellini, J. Chem. Soc., Dalton Trans., 1989, 25.
38. R. G. Holloway, B. R. Penfold, R. Colton and M. J. McCormick, J. Chem. Soc., Chem. Commun., 1976, 485.
39. (a) K. Umakoshi, A. Ichimura, I. Kinoshita and S. Ooi, Inorg. Chem., 1990, 29, 4005; (b) K. Umakoshi, I. Kinoshita and S. Ooi, Inorg. Chim. Acta, 1987, 127, L41.
40. (a) R. A. Stockland, G. K. Anderson and N. P. Rath, J. Am. Chem. Soc., 1999, 121, 7945; (b) M. L. Kullberg and C. P. Kubiak, Organometallics, 1984, 3, 632; (c) A. W. Hanson, A. J. McAlees and A. Taylor, J. Chem. Soc., Perkin Trans. 1, 1985, 441; (d) M. A. Khan and A. J. McAlees, Inorg. Chim. Acta, 1985, 104, 109; (e) G. Besenyei, C. L. Lee, J. Gulinski, S. J. Rettig, B. R. James, D. A. Nelson and M. A. Lilga, Inorg. Chem., 1987, 26, 3622; (f) J. A. Davies, A. A. Pinkerton, R. Syed and M. Vilmer, J. Chem. Soc., Chem. Commun., 1988, 47; (g) S. J. Young, B. Kellenberger, J. H. Reibenspies, S. E. Himmel, M. Manning, O. P. Anderson and J. K. Stille, J. Am. Chem. Soc., 1988, 110, 5744; (h) F. Neve, M. Longeri, M. Ghedini and A. Crispini, Inorg. Chim. Acta, 1993, 205, 15; (i) J. A. Davies, K. Kirschbaum and C. Kluwe, Organometallics, 1994, 13, 3664; (j) I. Foch, L. Parkanyi, G. Besenyei, L. I. Simandi and A. Kalman, J. Chem. Soc., Dalton Trans., 1999, 293; (k) R. A. Stockland, G. K. Anderson and N. P. Rath, Organometallics, 1997, 16, 5096; (l) C. Kluwe, J. Muller and J. A. Davies, J. Organomet. Chem., 1996, 526, 385; (m) G. Besenyei, L. Parkanyi, L. I. Simandi and B. R. James, Inorg. Chem., 1995, 34, 6118.
41. A. L. Balch, C. T. Hunt, C. L. Lee, M. M. Olmstead and J. P. Farr, J. Am. Chem. Soc., 1981, 103, 3764.
42. M. Kubiak, Acta Crystallogr., Sect. C, 1985, 41, 1288.
43. W. Clegg, C. D. Garner and M. H. Al-Samman, Inorg. Chem., 1982, 21, 1897.
44. D. P. Brancroft, F. A. Cotton, L. R. Falvello and W. Schwotzer, Inorg. Chem., 1986, 25, 1015.
45. C. L. Yao, L. P. He, J. D. Korp and J. L. Bear, Inorg. Chem., 1988, 27, 4389.
46. N. N. Greenwood and A. Earnshaw, in Chemistry of the Elements, Butterworth-Heinemann, London, 2nd edn, 1997.
47. I. Y. Guzmán-Jiménez and K. H. Whitmire, Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 1999, 55, IUC9900028.
48. K. C. Ho, G. M. McLaughlin, M. McPartlin and G. B. Robertson, Acta Crystallogr., Sect. B, 1982, 38, 421.
49. I. J. B. Lin, H. I. Shen and D. F. Feng, J. Chin. Chem. Soc. (Taipei), 1995, 42, 783 and references therein.
50. P. Bergamini, S. Sostero, O. Traverso, T. J. Kemp and P. G. Pringle, J. Chem. Soc., Dalton Trans., 1989, 2017.
51. (a) S. Al-Jibori, M. Hall, A. T. Hutton and B. L. Shaw, J. Chem. Soc., Chem. Commun., 1982, 1069; (b) S. Al-Jibori, M. Hall, A. T. Hutton and B. L. Shaw, J. Chem. Soc., Dalton Trans., 1984, 863.
52. (a) P. E. Garrou, Chem. Rev., 1985, 85, 171; (b) N. M. Doherty, G. Hogarth, S. A. R. Knox, K. A. McPherson, F. Melchior and A. G. Orpen, J. Chem. Soc., Chem. Commun., 1986, 540; (c) G. Hogarth, S. A. R. Knox and M. L. Turner, J. Chem. Soc., Chem. Commun., 1990, 145.

---