Palladium Pd2

SAXS data showed that the molecules of the palladium complex [Pd2(PPh2)H c]n are nearly spherical in shape with a diameter of 15.6 A. EXAFS data showed that both the platinum, [(PPh2)Pt]8 -io, and palladium, [Pd2(PPh2)Hx] , complexes contained only phosphorus and metal atoms in the first coordination sphere. The interatomic distance between Pt(Pd) and the phosphorus atoms is 2.26 A, which is typical of the Pt(Pd)-P distances in platinum and palladium complexes. Comparison with the spectral data of the reference compound, Pd(PPh3)4, showed that each platinum atom is surrounded by four phosphorus atoms (the coordination number, u(P/Pt), is four). The corresponding value for palladium atoms, (P/Pd), is three. 

Additionally, as pointed out earlier (Chapter 7, Section D7) with regard to vinyl halides, the Stille vide supra) reaction affords substitution of the leaving group by a carbon nucleophile at the site of unsaturation. Thus, as shown in the Equation 8.26, when the enol trifluorosulfonate (trillate, -OSO2CF3, -OTf) of 4-tert-butylcy-clohexanone (Chapter 9) is treated with tri-n-butylphenylstannane in the presence of a palladium catalyst (tris(dibenzylideneacetone)palladium, Pd2(dba)3) in a polar aprotic solvent (l-methyl-2-pyrrolidinone, A-methylpyrrolidinone [NMP]), substitution is readily affected. 

In the same year, Shaughness/s group [24] reported a trineopentylphosphane (TNpP) (Figure 2.3) that, in combination with palladium (Pd2(dba)3 or Pd(OAc)2 at 1-2 mol%), affords a very effective catalyst for the coupling of stericaUy demanding aryl chlorides and bromides with sterically hindered anilines. Excellent yields have been obtained even with 2,6-diisopropyl substituents. It is believed that the conformational flexibility of the TNpP ligand (noncyclic) plays a key role to allow the catalyst to couple with the hindered substrates. 

Synthesis. The most common staiting materials for palladium complexes are PdCl2 [7647-10-1] and [PdClJ [14349-67-8]. Commercially available materials useful for laboratory-scale synthesis iuclude [Pd2(OOCCH2)J [3375-31-3] [PdCl2(NCCgH )] [14220-64-5] [Pd(acac)2] [14024-61-4] [PdCl2(cod)] [12107-56-1], and [Pd(P(CgH5)3)J [14221-01-3]. 

A wide variety of complexes are formed by both metals in the +2 oxidation state indeed, it is the most important one for palladium. The complexes can be cationic, neutral or anionic. Both Pd2+ and Pt2+ are soft acids so that many stable complexes are formed with S or P as donor atoms but few with O-donors, though there are important ammines. There are pronounced similarities between corresponding palladium and platinum complexes the latter are more studied (and less labile). 

B. (E)-4-(2-Phenylethenyl)benzonitrile (2). An oven-dried, 250-mL, three-necked, round-bottomed flask equipped with an argon inlet adapter, rubber septum, glass stopper, and a teflon-coated magnetic stir bar is cooled to room temperature under a flow of argon. The flask is charged successively with bis (tri-tert-butylphosphinc)palladium [(Pd(P(t-Bu)3)2] (0.238 g, 0.466 mmol, 1.5 mol% Pd) (Notes 1, 2), tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3) (0.213 g, 0.233 mmol, 1.5 mol% Pd) (Note 3), and... 

From a practical point of view, it is worth noting that Heck reactions catalyzed by Pd/P( -Bu)3 do not typically require rigorously purified reagents or solvents. In addition, the palladium and phosphine sources, Pd[P(7-Bu)3]2 and Pd2(dba)3, are commercially available and can be handled in air. 

Palladium-catalyzed aminations of aryl halides is now a well-documented process [86-88], Heo et al. showed that amino-substituted 2-pyridones 54 and 55 can be prepared in a two-step procedure via a microwave-assisted Buchwald-Hartwig amination reaction of 5- or 6-bromo-2-benzyloxypyri-dines 50 and 51 followed by a hydrogenolysis of the benzyl ether 52 and 53, as outlined in Fig. 9 [89]. The actual microwave-assisted Buchwald-Hartwig coupling was not performed directly at the 2-pyridone scaffold, but instead at the intermediate pyridine. Initially, the reaction was performed at 150 °C for 10 min with Pd2(dba)3 as the palladium source, which provided both the desired amino-pyridines (65% yield) as well as the debrominated pyridine. After improving the conditions, the best temperature and time to use proved... 

Some of the details of the mechanism may differ for various catalytic systems. There have been kinetic studies on two of the amination systems discussed here. The results of a study of the kinetics of amination of bromobenzene using Pd2(dba)3, BINAP, and sodium r-amyloxide in toluene were consistent with the oxidative addition occurring after addition of the amine at Pd. The reductive elimination is associated with deprotonation of the animated palladium complex.166... 

A review10 with eight references describes the photochemical reactions of the binuclear palladium(0) complex [Pd2(dppm)3] (dppm = bis(diphenyl)phosphinomethane) with organic halides. 

Palladium dimethylsilanedithiolato complex is a precursor for Ti—Pd and Ti—Pd2 heterometal-lic complexes.311 The bis-silyl sulfides (R3Si)2S have been widely used to prepare a variety of metal sulfide clusters, because these reagents exploit the strength of the Si—O and Si—Cl bond to... 

The studies on palladium-phosphine complexes, especially those with diphosphine ligands, have mainly been focused on the complexes of palladium in lower oxidation state of 0 and 1 84,580,581,583,766,787,788,811-816 suc]1 as [Pd2(dppm)2]2+, [Pd2(dppm)3],815 [Pd3(dppm)3(/i3-... 

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