Iodine, oxidative-addition

In 2009, Marinetti and co-workers reported the preparation and structural data of NHC-Pt" complexes and their catalytic activity in model 1,6-enyne cycloisomerization reactions. The elaboration of square planar Pt" complexes bearing symmetric or unsymmetric chiral diphosphines was described in a sequence involving an iodine oxidative addition to a NHC-Pt complex and subsequent complexation of a chiral chelating diphosphine. In this context, the synthesis of a new family of Pt" six-membered metallacyclic NHC complexes was reported. This new platinacyclic complex was then used in an enantioselective 1,6-enyne cycloisomerization to afford, under mild conditions, the expected fused azabicycles in very high enantiomeric excesses and good to excellent yields [eqn (10.45)]. 

Sodium thiosulfate is determined by titration with standard iodine solution (37). Sulfate and sulfite are determined together by comparison of the turbidity produced when barium chloride is added after the iodine oxidation with the turbidity produced by a known quantity of sulfate iu the same volume of solution. The absence of sulfide is iadicated when the addition of alkaline lead acetate produces no color within one minute. 

Bromide ndIodide. The spectrophotometric determination of trace bromide concentration is based on the bromide catalysis of iodine oxidation to iodate by permanganate in acidic solution. Iodide can also be measured spectrophotometricaHy by selective oxidation to iodine by potassium peroxymonosulfate (KHSO ). The iodine reacts with colorless leucocrystal violet to produce the highly colored leucocrystal violet dye. Greater than 200 mg/L of chloride interferes with the color development. Trace concentrations of iodide are determined by its abiUty to cataly2e ceric ion reduction by arsenous acid. The reduction reaction is stopped at a specific time by the addition of ferrous ammonium sulfate. The ferrous ion is oxidi2ed to ferric ion, which then reacts with thiocyanate to produce a deep red complex. 

The Perkin reaction is of importance for the iadustrial production of coumarin and a number of modifications have been studied to improve it, such as addition of a trace of iodine (46) addition of oxides or salts of metals such as iron, nickel, manganese, or cobalt (47) addition of catalytic amounts of pyridine (48) or piperidine (49) replacement of sodium acetate by potassium carbonate (50,51) or by cesium acetate (52) and use of alkaU metal biacetate... 

The disulfide is a moderately strong oxidant and liberates iodine on addition of an acidified iodide solution. As usual there is a reversible... 

The 3,5-bis(trifluoromethyl)pyrazolate analog [Ir(cod)(/x-3,5-(CF3)2pz)]2 does not enter into oxidative addition with iodine, methyl iodide, or acetylenes. The mixture of pyrazolate and 3,5-bis(trifluoromethyl)pyrazolate gives [(rj -codllrf/x-pz)(/L-3,5-(CF3)2pz)Ir(rj -cod)], which reacts with bis(trifluoromethyl)acetylene in a peculiar manner [83JCS(CC)580], producing 145, where 3,5-bis(trifluoromethyl) pyrazolate is replaced by the ethylene bridge and the rj -coordination mode of one of the cod ligands is converted into the rj -allylic mode. 

Complex [(CXI )Ir(/j,-pz)(/i,-SBu )(/j,-Ph2PCH2PPh2)Ir(CO)] reacts with iodine to form 202 (X = I) as the typical iridium(II)-iridium(II) symmetrical species [90ICA(178)179]. The terminal iodide ligands can be readily displaced in reactions with silversalts. Thus, 202 (X = I), upon reaction with silver nitrate, produces 202 (X = ONO2). Complex [(OC)Ir(/i,-pz )(/z-SBu )(/i-Ph2PCH2PPh2)Ir(CO)] reacts with mercury dichloride to form 203, traditionally interpreted as the product of oxidative addition to one iridium atom and simultaneous Lewis acid-base interaction with the other. The rhodium /i-pyrazolato derivative is prepared in a similar way. Unexpectedly, the iridium /z-pyrazolato analog in similar conditions produces mercury(I) chloride and forms the dinuclear complex 204. 

It has been suggested that the initial formation of iodine on addition of iodide to a diazonium salt solution is caused by oxidation of the iodide by excess nitrite from the preceding diazotization. Packer and Taylor (1985) demonstrated that, if urea was added as a nitrite scavenger (see Sec. 2.1) to a diazotization solution, that solution produced iodine much more rapidly than a portion of the same diazonium salt solution not containing urea, but eventually the latter reaction too appeared to follow the same course. This confirms the role of excess nitrite, and suggests that the iodo-de-diazoniation steps only occur in the presence of iodine or triiodide (I -). The same authors also found that iodo-de-diazoniation is much slower under nitrogen. All these observations are consistent with radical-chain processes, but not with a heterolytic iodo-de-diazoniation. 

Table 1 Examples of treatment with iodine leading to oxidation, addition or substitution products.

Iodine is enriched to a greater extent in chromatogram zones coated with lipophilic substances than it is in a hydrophilic environment. Hence, iodine is only physically dissolved or adsorbed. Occasionally a chemical reaction also takes place, such as, for example, with estrone [19] (cf. Iodine Reagents ). In general it may be said that the longer the iodine effect lasts the more oxidations, additions or electrophilic substitutions are to be expected. 

Oxidative-addition of iodine also was investigated for the complex C -bzimAu]3. This complex behaves like most of the CTCs since it adds iodine at only one gold center to yield [p,-N, C -bzimAu]3l2 [59]. The X-ray structure shows that it consists of discrete trinuclear units with the three gold atoms bridged by 1 -benzylimidazolates. 

Residual N-bromosuccinimide from the manufacturing process may be identified and/or quantified by making use of its oxidation potential by titration of liberated iodine after addition of potassium iodide in acetic acid (25). 

The oxidative addition of iodine to diorganotellurides has also been examined by stopped-flow spectroscopy. The initial fast reaction of iodine with diphenyltellur-ide (23), di-4-methoxyphenyltelluride (24), A,V-dimethyl-2-(aminomethyl)phenyl-telluride (17), and 2,6-di-tert-butyltelluropyran-4-one (25) displays inverted Arrhenius behavior (negative values of E ), which is consistent with a preequilibrium involving higher-order iodine species as shown in equation (6). The I4 species is the actual oxidant for diorganotellurides as shown in equation (7). Thus, the initial reaction is formation of the r i-association complex of I4 with the... 

A quinazoline-2,4-dithione complex [Pd(LH)3(PPh3)] has been isolated from the reaction of the free ligand LH (51) with [Pd(PPh3)4], Unidentate co-ordination of the ligand via a sulphur atom was confirmed from the i.r. spectrum. Oxidative addition with iodine is reported. ... 

Thioamides are reducing agents. They inhibit thyroid hormone synthesis by inhibiting the peroxidase enzymatic system, which catalyzes oxidation of iodide ions and iodine that are consumed in food, which is necessary for iodination of tyrosine derivatives. Thus they reduce the concentration of free iodine necessary to react with tyrosine derivatives, and they can also block oxidative addition reactions of mono- and diiodtyrosines, which form L-thyroxine and L-triiodothyronin. 

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