II Compounds

Preparation of Chromium(II) Chloride. (Perform one of the following two experiments.) 1. Put several pieces of metallic chromium into a test tube, pour in 2-3 ml of a 20% hydrochloric acid solution, and insert a stopper with a gas-discharge tube. Connect to the latter a rubber tube with a slot closed by a glass rod (a Bunsen valve. Fig. 125). What is the role of the slot in the rubber tube Identify the substance in the solution. Write the equation of the reaction. 

Put a few pieces of zinc into a small flask, pour in 2-3 ml of a chromium(III) chloride solution, 5-10 ml of a 10% hydrochloric 

Properties of Chromium(II) Chloride. Perform all experiments with chromium(II) chloride rapidly Why  

Pour several millilitres of the obtained chromium(II) chloride solution into a test tube and let it stand in the air. How does the colour of the solution change What properties are exhibited by the chromium(II) chloride Write the equation of the reaction. 

Put a few sodium acetate crystals into a test tube and add a chro- 

Pour several millilitres of the obtained chromium(II) chloride 

Chlorotris (dimethyl sulfide) platinum (II) tetrafluoroborate was prepared by Gog-gin et al. using cis-[Pt(Me2S)2Cl2] as a starting material.1 The corresponding tetraphenylborate was prepared like the tetrafluoroborate. 

A modification of the method of Goggin et al. for the preparation of chlorotris (dimethyl sulfide) platinum (II) complexes is described in this synthesis. 

The corresponding tetraphenylborate is prepared by dropwise addition of the filtrate containing the nitrate complex to a cold ethanol solution containing the calculated amount of sodium tetraphenylborate instead of hydrogen tetrafluo- 

Structural Data of Chalcogen Halides of the Types XYj and X2Y2 

Compound Method X-X distance (A) X-Y distance (A) Bond angle ( ) Dihedral angle (°) Reference 

The new compound SFCl was prepared by UV photolysis of FC(0)SC1 in argon matrix and by UV photolysis of CI2/SF3SF in the gas phase and characterized by detailed vibrational analysis in the matrix (436). 

In the course of a recent low-temperature study of the system S/Cl it was possible to prepare single crystals of SCI2 and to determine the solid-state structure at - 134°C (233). As shown in Fig. 26, there are two independent angular molecules in the unit cell that are weakly associated through S--C1 and S---S contacts to form bimolecular layers and that have intramolecular dimensions very close to the values of the free gaseous molecule (322,432) (Table 11). Additional literature on properties of the chalcogen dihalides is abstracted in (160). 

Some clarifying preparative and spectroscopic work has been reported on the existence and properties of iodosulfanes. Earlier UV/vis-spectroscopic studies have proposed diiododisulfane and diiodopolysul-fanes S l2 (n = 2. . . 6) to exist as more or less short-lived species in solution (111). Solid disulfur diiodide in a mixture with other products 

---

Cr(02CCH3)2]2,2H20. Red insoluble compound formed from sodium ethanoate and CrC)2 in aqueous solution. The most stable Cr(II) compound contains a Cr —Cr bond, chromium fluorides... 

Cobalt(II) compounds are often incorporated in the gel. When the gel has absorbed a fair amount of moisture it will turn pink but will revert to blue on heating. 

In both cases, the precipitate must be filtered and dried quickly, by washing first with alcohol and then with ether (to prevent formation of the copper(II) compound). 

This copper(I) compound, unlike the above, is soluble in water and therefore in the presence of water liberates copper and forms a copper(II) compound ... 

Group II. Compounds soluble in water, but insoluble in ether. 

In organic synthesis, two kinds of Pd compounds, namely Pd(II) salts and Pd(0) comple.xes, are used. Pd(II) compounds are used either as stoichiometric reagents or as catalysts and Pd(0) complexes as catalysts. Pd(Il) compounds such as PdCh and Pd(OAc)2 are commercially available and widely used as... 

Stoichiometric Oxidative Reactions with Pd(II) Compounds in which Pd(II) is Reduced to Pd(0)... 

The Pd—C cr-bond can be prepared from simple, unoxidized alkenes and aromatic compounds by the reaction of Pd(II) compounds. The following are typical examples. The first step of the reaction of a simple alkene with Pd(ll) and a nucleophile X or Y to form 19 is called palladation. Depending on the nucleophile, it is called oxypalladation, aminopalladation, carbopalladation, etc. The subsequent elimination of b-hydrogen produces the nucleophilic substitution product 20. The displacement of Pd with another nucleophile (X) affords the nucleophilic addition product 21 (see Chapter 3, Section 2). As an example, the oxypalladation of 4-pentenol with PdXi to afford furan 22 or 23 is shown. 

Palladation of aromatic compounds with Pd(OAc)2 gives the arylpalladium acetate 25 as an unstable intermediate (see Chapter 3, Section 5). A similar complex 26 is formed by the transmetallation of PdX2 with arylmetal compounds of main group metals such as Hg Those intermediates which have the Pd—C cr-bonds react with nucleophiles or undergo alkene insertion to give oxidized products and Pd(0) as shown below. Hence, these reactions proceed by consuming stoichiometric amounts of Pd(II) compounds, which are reduced to the Pd(0) state. Sometimes, but not always, the reduced Pd(0) is reoxidized in situ to the Pd(II) state. In such a case, the whole oxidation process becomes a catalytic cycle with regard to the Pd(II) compounds. This catalytic reaction is different mechanistically, however, from the Pd(0)-catalyzed reactions described in the next section. These stoichiometric and catalytic reactions are treated in Chapter 3. 

Reactions Involving Pd(II) Compounds and Pd(0) Complexes ic-Allyl complex formation and its reaction with a nucleophile... 

Reactions of another class are catalyzed by Pd(II) compounds which act as Lewis acids, and are treated in Chapter 5 and partly in Chapter 4. From the above-mentioned explanation, the reactions catalyzed by Pd(0) and Pd(II) are clearly different mechanistically. In this book the stoichiometric and catalytic reactions are classified further according to reacting substrates. However, this classification has some problems, viz. it leads to separate treatment of some unit reactions in different chapters. The carbonylation of alkenes is an example. Oxidative carbonylation of alkenes is treated in Chapter 3 and hydrocar-bonylation in Chapter 4. 

Pd(II) compounds coordinate to alkenes to form rr-complexes. Roughly, a decrease in the electron density of alkenes by coordination to electrophilic Pd(II) permits attack by various nucleophiles on the coordinated alkenes. In contrast, electrophilic attack is commonly observed with uncomplexed alkenes. The attack of nucleophiles with concomitant formation of a carbon-palladium r-bond 1 is called the palladation of alkenes. This reaction is similar to the mercuration reaction. However, unlike the mercuration products, which are stable and isolable, the product 1 of the palladation is usually unstable and undergoes rapid decomposition. The palladation reaction is followed by two reactions. The elimination of H—Pd—Cl from 1 to form vinyl compounds 2 is one reaction path, resulting in nucleophilic substitution of the olefinic proton. When the displacement of the Pd in 1 with another nucleophile takes place, the nucleophilic addition of alkenes occurs to give 3. Depending on the reactants and conditions, either nucleophilic substitution of alkenes or nucleophilic addition to alkenes takes place. 

Oxidative Reactions with Pdf II) Compounds Ph3P=CH0Ma... 

---