Polypyrrole-palladium (PPy-Pd) nanocomposite was deposited in situ from aqueous solution onto micrometer-sized polystyrene (PS) latex particles. The PS seed particles and resulting composite particles were extensively characterized with respect to particle size and size distribution, morphology, surface/bulk chemical compositions, and conductivity. PPy-Pd nanocomposite loading onto the PS seed latex particles was systematically controlled over a wide range (10-60 wt %) by changing the weight ratio of the PS latex and PPy-Pd nanocomposite. Pd loading was also controlled between 6 and 33 wt %. The conductivity of pressed pellets increased with the PPy-Pd nanocomposite loading and four-point probe measurements indicated conductivities ranging from 3.0 x 10(-1) to 7.9 x 10(-6) S cm(-1). Hollow capsule and broken egg-shell morphologies were observed by scanning/transmission electron microscopy after extraction of the PS component from the composite particles, which confirmed a PS core and PPy-Pd nanocomposite shell morphology. X-ray diffraction confirmed that the production of elemental Pd and X-ray photoelectron spectroscopy indicated the existence of elemental Pd on the surface of the composite particles. Transmission electron microscopy confirmed that nanometer-sized Pd particles were distributed in the shell. The nanocomposite particles functioned as an efficient catalyst for Suzuki-type coupling reactions in aqueous media for the formation of carbon-carbon bonds.

Linear polystyrene-stabilized PdO nanoparticles (PS-PdONPs) were prepared in water by thermal decomposition of Pd(OAc)(2) in the presence of polystyrene. The immobilization degree of palladium was dependent on the molecular weight of polystyrene, while the size of the Pd nanoparticles was not. Linear polystyrene-stabilized Pd nanoparticles (PS-PdNPs) were also prepared using NaBH(4) and phenylboronic acid as reductants. The catalytic activity of PS-PdONPs was slightly higher than that of PS-PdNPs for Suzuki coupling reaction in water. PS-PdONPs exhibited high catalytic activity for Suzuki and copper-free Sonogashira coupling reactions in water and recycled without loss of activity.

The C-S bond activation by transition-metal complexes has received increasing attention for efficient catalytic and stoichiometric transformations using organic sulfides. For example, great effort has been devoted to the cleavage of the thiophen C-S bond to get insight about hydrodesulfurization that is of great importance in petrochemistry. 1 The oxidative addition (OA) of the C-S bond has also been reported on aryl-S, 2 allyl-S, 3 aroyl-S, 4 imidoyl-S, 5 and strained alkyl-S 6 bonds. However, the fundamental insight on the OA of acyclic vinyl sulfide 1 to low-valent metal (M) (Scheme 1), the simplest sp 2 -C-S bond cleavage, is much more sparse, though the process has been postulated to be involved in a number of nickel-catalyzed cross coupling reactions using 1 and organometallic reagents. 7 To our knowledge, since an early example of OA of 1 with Fe 2 (CO) 10 affording a dinuclear complex in 1961, 8 no practical progress has been made to shed light on such a fundamental subject in organometallic chemistry. 9 We wish to report here the first example of OA of 1 to Pt(0) (M ) Pt), in which substituents at A and B in 1 are proved to play a pivotal role in realizing the reaction. A variety of vinyl sulfides 1 shown in Scheme 2 were prepared and the feasibility of OA to Pt(PPh 3 ) 2 (C 2 H 4 ) (2) was investigated (eq 1 and Table 1). After many attempts, we have ultimately found that the reaction of (Z)-1,2-bis(p-tolylthio)styrene (1a) with 2 under very mild conditions (25°C) in benzene indeed provided the desired OA product cis-Pt[(Z)-C(H)dC(Stol-p)(Ph)](Stol-p)(PPh 3 ) 2 (3a)in 78% isolated yield as a single product by simple filtration of the crude reaction mixture (eq 1). The 31 P NMR spectrum of 3a showed a couple of doublets centered at δ 18.9 (J P-P ) 17 Hz, J Pt-P ) 1847 Hz) and δ 20.1 (J P-P ) 17 Hz, J Pt-P ) 3240 Hz), meaning two PPh 3 s positioned cis. No intermediates or byproducts were observed, when a small-scale reaction was monitored by 1 H and 31 P NMR spectra (run 2). Because the complex 3a isomerized to trans-isomer in C 6 D 6 at 50°C in the presence of PPh 3 (cis/trans ) 20/80 after 22 h), the cis-3a was definitely the kinetic product of the OA of 1a to 2. Although efforts to obtain a high-quality crystal of 3a were unsuccessful, a single X-ray crystallographic analysis of Pt[(Z)-C(H)dC(Stol-p)(C 6 H 4 Cl-p)]-(Stol-p)(DPPE) (4; DPPE; bis(diphenylphosphino)ethane) produced by the OA of 1c to 2 followed by the clean PPh 3 -for-DPPE substitution demonstrated that OA took place at the terminal vinyl-C-S bond with the stereochemistry of the vinyl moiety retained (Figure 1). 10 The OA of the E-isomer 1b to 2 provided 86% of cis-Pt[(E)-C(H)dC(Stol-p)(Ph)](Stol-p)(PPh 3 ) 2 (3b) by a similar preparative (1) For recent examples: (a) Αrévalo, A.; Bernés, S.; Garcia, J. J.; Maitlis, P. M. (a) Okamura, H.; Miura, M.; Takei, H. Tetrahedron Lett. 1979, 43. (b) Cristau, H. J.; Chabaud, B.; Labaudiniere, R.; Christol, H. J. Org. Chem. 1986, 51, 875. (c) Cristau, H. J.; Chabaud, B.; Labaudiniere, R.; Christol...

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Palladium nanoparticles can be readily stabilized onto linear polystyrene by a simple procedure. The resultant polystyrene-stabilized Pd has high catalytic activity for Suzuki-Miyaura cross-coupling reaction in water and can be reused without loss of activity.