Oxidative Addition of Aryl Disulfides to Pd(0) Complexes: Synthesis and Structures of Bis(thiolato) Pd(II) Complexes

Experimental

General Procedures. All manipulations of air-sensitive compounds were performed under N2 or Ar by standard Schlenk techniques. Solvents were distilled from Na–benzo-phenone. The analytical laboratories at Kangnung–Wonju National University carried out elemental analyses with CE instruments EA1110. IR spectra were recorded on a Perkin Elmer BX spectrophotometer. NMR (1H, 13C{1H}, and 31P{1H}) spectra were obtained on a JEOL Lamda 300 and ECA 600 MHz spectrometer. Chemical shifts were referenced to internal Me4Si or to external 85% H3PO4. X-ray analyses were obtained at Korea Basic Science Institute (Jeonju center) and CCRF (Cooperative Center for Research Facilities in the Sungkyunkwan University). Trans-[PdEt2(PR3)2] (R = PMe3, PEt3) was prepared by the literature method.10 Phenyl disul-fide, thienyl disulfide, dianiline disulfide and p-tolyl disulfide were commercially available.

Scheme 3

Figure 1.ORTEP drawing of compound 1 with 50% probability thermal ellipsoids. Labeled atoms with “A” are related to un-labeled ones by the crystallographic inversion symmetry. Selected bond lengths (Å) and angles (°): Pd1–P1 2.3153(6), Pd1–S1 2.3391(5), Pd2–P2 2.3145(6), Pd2–S2 2.3434(5), Cl1–C4 1.747(2), Cl2–C10 1.747(2); P1–Pd1–S1 86.88(2), P1–Pd1–S1A 93.12(2), P1–Pd1–P1A 180.00(2), P2-Pd2–S2 92.95(2), P2–Pd2–S2A 87.05(2), P2A –Pd2–P2, 180.00(3).

Figure 2.ORTEP drawing of compound 3 with 40% probability thermal ellipsoids. Labeled atoms with “A” are related to unlabeled ones by the crystallographic inversion symmetry. Selected bond lengths (Å) and angles (°): Pd1–P1 2.3185(4), Pd1–S1 2.3358(4), S1–C1 1.753(2); P1–Pd1–S1 93.46(14), C1–S1–Pd1 108.47(5).

Preparation of trans-[Pd(SC6H4-p-Cl)2(PR3)2] (PR3 = PMe3, (1); PEt3, (2)). Styrene (78 μL, 0.68 mmol) and tetra-hydrofuran (THF, 3 mL) were added sequentially to a Schlenk flask containing trans-[PdEt2(PMe3)2] (0.107 g, 0.34 mmol) at 0 °C. The mixture was heated at 55 °C for 30 min to give a yellow solution. p-Chlorophenyl disulfide (0.049 g, 0.17 mmol) was added to the mixture at room temperature, and then the yellow solution turned into a dark yellow solution. After stirring for 2 h at room temperature, the solvent was completely removed under vacuum, and then the resulting residue was solidified with hexane. The solids were filtered and washed with hexane (2 mL × 2) to obtain the crude solids. Recrystallization from CH2Cl2/n-hexane afforded pale yellow crystals of trans-[Pd(SC6H4-p-Cl)2-(PMe3)2] (1, 0.067 g, 73%). C18H26Cl2P2S2Pd (545.80): calcd. C 39.61, H 4.80, S 11.75; found C 39.33, H 4.87, S 11.45. 1H NMR (300 MHz, CDCl3) δ 1.36 (t, J = 3.3 Hz, 18H, P(CH3)3), 7.01 (m, 4H, Ar–H), 7.43 (m, 4H, Ar–H). 13C{1H} NMR (75 MHz, CDCl3) δ 13.7 (t, Jcp = 16 Hz, P(CH3)3), 127.7, 127.8, 132.1 (t, JCP = 1.2 Hz, Ar), 146.1. 31P{1H} NMR (120 MHz, CDCl3) δ 12.9 (s).

Figure 3.ORTEP drawing of compound 5 with 40% probability thermal ellipsoids. Labeled atoms with “A” are related to un-labeled ones by the crystallographic inversion symmetry. Selected bond lengths (Å) and angles (°): Pd1–P1 2.3175(7), Pd1–S1 2.3422(6), S1–C1 1.739(2), S2–C4 1.701(3), S2–C1 1.720(2); P1–Pd1–P1A 180.00(3), P1–Pd1–S1 87.06(3), P1–Pd1–S1A 92.94(3), C1–S1–Pd1 105.37(8), C4–S2–C1 92.38(14).

Complex 2 (92%) was analogously prepared using a 1:1 molar ratio of trans-[PdEt2(PEt3)2] and p-chlorophenyl di-sulfide. C24H38Cl2P2S2Pd (629.96): calcd. C 45.76, H 6.08, S 10.18; found C 45.78, H 6.10, S 9.79. 1H NMR (300 MHz, CDCl3) δ 1.02 (quin, J = 8.0 Hz, 18H, P(CH2CH3)3), 1.82 (m, 12H, P(CH2CH3)3), 7.0 (m, 4H, Ar–H), 7.42 (m, 4H, Ar–H). 13C{1H} NMR (75 MHz, CDCl3) δ 8.28 (s, P(CH2CH3)3), 13.8 (t, JCP = 14 Hz, P(CH2CH3)3), 127.4, 127.6, 132.3, 146.0. 31P{1H} NMR (120 MHz, CDCl3) δ 14.9 (s).

Complex 1 could also be synthesized via an alternate route. p-Chlorophenyl disulfide (0.236 g, 0.82 mmol) and THF (6 mL) were added to a Schlenk flask containing trans-[PdEt2(PMe3)2] (0.524 g, 1.65 mmol) at 0 °C. After stirring the reaction mixture for 18 h at room temperature, the solv-ent was completely removed under vacuum to obtain crude solids which were recrystallized from CH2Cl2/n-hexane (0.313 g, 69%).

Preparation of trans-[Pd(SC6H4-p-Cl)2(PMePh2)2], (3). p-Chlorophenyl disulfide (0.123 g, 0.43 mmol) and CH2Cl2 (2 mL) were added to a Schlenk flask containing [Pd(PMePh2)4] (0.387 g, 0.43 mmol) at room temperature. The initial red solution turned to a dark yellow solution. After the resulting mixture was stirred for 12 h, the solvent was completely removed under vacuum, and then the resulting residue was solidified with diethyl ether. The resulting solids were filter-ed and washed with hexane (2 mL × 2) to obtain the crude solids. Recrystallization from CH2Cl2/n-hexane afforded brown crystals of trans-[Pd(SC6H4-p-Cl)2(PMePh2)2], (3, 0.321 g, 95%). C38H34Cl2P2S2Pd (794.08): calcd. C 57.48, H 4.31, S 8.08; found C 57.03, H 4.31, S 7.75. 1H NMR (300 MHz, CDCl3) δ 1.91 (t, J = 3.3 Hz, 6H, P(CH3)Ph2), 6.65 (m, 4H, Ar-H), 6.96 (m, 4H, Ar–H), 7.22-7.36 (m, 12H, Ar–H), 7.45-7.52 (m, 8H, Ar-H). 13C{1H} NMR (75 MHz, CDCl3) δ 13.0 (t, Jcp = 16 Hz, P(CH3)Ph2), 127.1, 127.6, 128.1 (t, JCP = 5.0 Hz, Ar), 130.0, 132.2, 132.5 (t, JCP = 6.2 Hz, Ar), 132.9, 145.1. 31P{1H} NMR (120 MHz, CDCl3) δ 9.1(s).

Preparation of trans-[Pd(S-C6H5)2(PMe3)2] (4), trans-[Pd(S-C4H3S)2(PMe3)2] (5), and trans-[Pd(SC6H4-P-X)2-(PMe3)2] (X = NH2, (6); X = Me, (7)). Styrene (114 μL, 0.99 mmol) and THF (3 mL) were sequentially added to a Schlenk flask containing trans-[PdEt2(PMe3)2] (0.157 g, 0.50 mmol) at 0 °C. The mixture was heated at 55 °C for 30 min to give a yellow solution. Phenyl disulfide (0.108 g, 0.50 mmol) was added to the mixture at room temperature, and then the initial orange solution turned into a yellow suspension. After stirring for 2 h, the solvent was completely removed under vacuum, and then the resulting solids were filtered and washed with hexane (2 mL × 3) to obtain the crude solids. Recrystallization from CH2Cl2/hexane gave yellow crystals of trans-[Pd(S-C6H5)2(PMe3)2] (4, 0.159 g, 73%). C14H24P2S2Pd (476.91): calcd. C 45.33, H 5.92, S 13.45; found C 45.29, H 5.98, S 13.22. 1H NMR (300 MHz, CDCl3) δ 1.35 (t, J = 3.3 Hz, 18H, P(CH3)3), 6.91–6.96 (m, 2H, Ph), 7.04–7.09 (m, 4H, Ph), 7.54–7.57 (m, 4H, Ph). 13C{1H} NMR (75 MHz, CDCl3) δ 13.7 (t, Jcp = 16 Hz, P(CH3)3), 122.0, 127.8, 131.3 (t, Jcp = 1.2 Hz, Ph–C), 147.4. 31P{1H} NMR (75 MHz, CDCl3) δ −13.1(s).

The formation of complex 4 was confirmed by comparing its spectral data with those reported previously.17,18 Complexes 5–7 were analogously prepared. Spectroscopic data are sum-marized in Supporting Information.

X-ray Structure Determination. All X-ray data were collected on a Bruker Smart APEX or APEX2 diffractometer equipped with a Mo X-ray tube. Collected data were correct-ed for absorption with SADABS based upon the Laue sym-metry by using equivalent reflections.19 All calculations were carried out with SHELXTL programs.20 All structures were solved by direct methods.

Crystallographic data for the structural analysis have been deposited at the Cambridge Crystallographic Data Centre, CCDC No. 954099 (for 1) and 954100 (for 3) and 954101 (for 5). Copies of this information may be obtained free of charge from: The director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (Fax: +44-1223-336-033; E-mail: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).