Lead dihalides, reactions

Hal = F, Cl, Br, I), a solid state reaction between germanium sulfide and suitable lead dihalides at ca 570 K was used304-306. The observed IEs, corresponding to ionizations from the valence shell MOs, are presented in Table 11. 

Addition to the Double Bond. Chlorine, bromine, and iodine react with aHyl chloride at temperatures below the inception of the substitution reaction to produce the 1,2,3-trihaLides. High temperature halogenation by a free-radical mechanism leads to unsaturated dihalides CH2=CHCHC1X. Hypochlorous and hypobromous acids add to form glycerol dihalohydrins, principally the 2,3-dihalo isomer. Dehydrohalogenation with alkah to epicbl orobydrin [106-89-8] is ofgreat industrial importance. 

Hydrogen hahdes normally add to form 1,2-dihaLides, though an abnormal addition of hydrogen bromide is known, leading to 3-bromo-l-chloropropane [109-70-6], the reaction is beUeved to proceed by a free-radical mechanism. Water can be added by treatment with sulfuric acid at ambient or lower temperatures, followed by dilution with water. The product is l-chloro-2-propanol [127-00-4]. 

The chemistry of alkynes is dominated by electrophilic addition reactions, similar to those of alkenes. Alkynes react with HBr and HC1 to yield vinylic halides and with Br2 and Cl2 to yield 1,2-dihalides (vicinal dihalides). Alkynes can be hydrated by reaction with aqueous sulfuric acid in the presence of mercury(ll) catalyst. The reaction leads to an intermediate enol that immediately isomerizes to yield a ketone tautomer. Since the addition reaction occurs with Markovnikov regiochemistry, a methyl ketone is produced from a terminal alkyne. Alternatively, hydroboration/oxidation of a terminal alkyne yields an aldehyde. 

The reaction of cobaltocene with organoboron dihalides RBX2 (R = Me, Ph and X = Cl, Br mainly) and boron trihalides (BC13, BBr3) leads essentially to three types of (boratabenzene) cobalt complexes, 19,20, and 21 (7,57). CoCp2 plays a dual role in part it acts as a reductant, in part it... 

Also the reaction of triphenylarsenic dihalides with acetonitrile leads to the onium compounds.243,244 An example... 

Ph4Sb0NC(CN)C(0)NH2,249 possess trigonal bipyramidal geometries.250 Reactions of the Martin ligand with triorganobismuth dihalides leading to cyclic tetraorganobismuth compounds are shown in Scheme 23.251... 

Before the mechanism of vinyl polymerization was understood, the question of the structure of vinyl polymers was of considerable interest. Staudinger had written these polymers as having a head-to-tail arrangement of recurring units, but he had not really furnished evidence of the structure. As Carothers once said, Staudinger had assigned the structure by pronouncement. He was as usual correct, and chemical evidence was developed to establish such structures. For example, when monovinyl methyl ketone polymerized, it could produce by head-to-head, tail-to-tail reaction a 1,4-diketone. By head-to-tail polymerization it would give a 1,5-diketone. These two types have different reactions. The study of the polymer proper showed that the polymer was a 1,5-diketone. In the case of polyvinyl chloride, a head-to-head, tail-to-tail polymerization would lead to a 1,2-dihalide compound, and a head-to-tail polymerization would lead to a 1,3-dihalide. 

Tetramethyl- or tetraphenyl- (cyclobutadiene)nickel dihalides undergo reductive ligand substitution with nitrogen donor ligands such as 2,2 -bipyridine or 1,4-diaza-1,3-dienes with the addition of sodium metal237. The 2,2/-bipyridyl ligand is readily displaced and reaction of this complex with a variety of olefins and alkynes leads to cycloaddition reactions with the cyclobutadiene ligand. 

Direct treatment of organic geminal dihalides or trihalides with strongly nucleophilic transition metal complexes can also lead to the formation of carbene complexes, presumably via intermediate a-haloalkyl complexes [484-489]. Examples of such reactions are sketched in Figure 3.17. 

Several titanocene derivatives containing silsesquioxane ligands have also been prepared and characterized. It soon turned out that reactions of 3 or its mono-silylated derivative 12 with titanocene dihalides are not straightforward and usually lead to the formation of product mixtures. A common feature appears to be the formation of p-oxo species despite the use of carefully dried solvents. Although at this stage the occurrence of partial hydrolysis cannot completely be ruled out, we... 

Palladium-catalyzed a-arylation of ketones is performed with arylene dihalides and bifunctional aromatic ketones 148 to result in the bond formation at the r/) -a-carbon of the ketone, leading to polyketone 149. The reaction is carried out in the presence of Pd(0) and various phosphines. Several bidentate phosphines and bulky alkylphosphines such as dppf, BINAP, PCys, and P Bu3 are shown to be effective, while PPh3 results in no reaction. Arylene dibromide and diiodide are applicable as the co-monomers. The polymerization reaction is carried out in THE in the presence of NaO Bu at 75 °C under N2, and polymers 149 are isolated in 60-80% yields (M = 7000-15 000). Polyketone 149 is further transformed to conjugated polymer PPV by reduction of the ketone moiety with LiAlH4 followed by dehydration with an acid (Equation (69)). 

The palladium-catalyzed amination reaction with a monofunctional primary amine 167 effects i / -diarylation to afford the tertiary amine polymers 168. Hence, polycondensation of 167 with bifunctional arylene dihalides leads to 168 (Equation (81)). Polycondensation of a primary amine bearing an azobenzene moiety with dibromides in the presence of Pd2(dba)3 (2.5mol%)- Bu3P (P/Pd = 3 l) and NaO Bu at 100°G for 24h in toluene gives 168 in 81-93% yields, as reported by Kanbara. 

Ring expansion of the six-membered ketosulfide (371) produces both 5-thiocanone and 4-thiocanone [372 v 1700 cm-1 (neat)], but in low yields (70JOC584). The photochemistry of these ketones has been studied and leads to a variety of products in low yields (70JOC584). 3-Thiocanone (373 b.p. 66-68 °C/0.35 mmHg, v 1708 cm-1) is formed in 44% yield by the dihalide method, but in only 3% yield by the Dieckmann reaction under high dilution conditions (70JPR1058). 

The solvolysis of 7,7-dibromo-bicyclo[4.1.0]heptane in methanol in the presence of silver perchlorate leads to ( -2-bromo-3-methoxycyeloheptene [172, 173]. A more detailed study of this reaction — having been performed by Ito in 1986 [174] — has revealed that the stereochemical result of the solvolysis depends on the length of the polymethylene chain in these bicyclic dihalides. For the lower homologs (n = 2 to 4) it is the ( )-isomer XIII that is produced, whereas for the more extended systems (n = 5 to 8) the Z-bromoethers XIV are produced. 

---