Iodine bond

This equilibrium is established when hydrogen iodide is heated, hydrogen-iodine bonds being broken. 

All the OsNX4 complexes are distorted square pyramids (with N-Os-X angles of 103.7 to 104.5°) [188]. The stability of an osmium(VI) to iodine bond is unusual and is presumably owing to the extensive Os=N 7r-bonding reducing the positive charge on the metal and stabilizing it to reduction. 

Another domino radical cyclization approach, which allows construction of the B- and E-rings of the alkaloid ( )-aspidospermidine (3-46), has been described by the same group [25]. Transformation of the iodoazide 3-44 into the tetracycle 3-45 was accomplished in 40 % yield by selective attack at the carbon-iodine bond in the... 

The important observation is that all of the isotope effects are large and inverse. Therefore, the transition states in these reactions must be very crowded, i.e. the Ca—H(D) out-of-plane bending vibrations in the transition state must be high energy (Poirier et al., 1994). As a result, these workers concluded that nitrogen-a-carbon bond formation is more advanced than a-carbon-iodine bond rupture in the transition state. It is interesting, however, that in spite of the small secondary a-deuterium KIEs, these authors concluded that the N—C bond formation is only approximately 30% complete in the transition state. 

Photolysis of the carbon-iodine bond in iodo-perfluoroalkyl compounds has been employed to enable the formation of the corresponding pefluoroalkyl radical [37]. Different perfluorinated alkyl chains can thus be covalently bound to the CNT. Interestingly, the authors reported that no change in solubility of the nanotubes was noted after the perfluoro-alkylation. 

Tertiary alkyl halides are easier to reduce than secondary alkyl halides, which are easier to reduce than primary alkyl halides. Carbon-iodine bonds are easier to reduce than carbon-bromine bonds, which are easier to reduce than carbon-chlorine bonds [1-3]. 

The lactam formation from the oxidation of cyclic amines (353, for example) probably proceeds via intermediate 364. The nitrogen-iodine bond dissociates to give imine 365, which reacts again with a second equivalent of iodosobenzene to give another intermediate 366. Finally, 366 on reductive... 

Recently, a reductive magnesium insertion into a carbon-iodine bond of a / -iodo-a-ketoester has been described. The preparation of the iodomagnesium enolate 17 derived from an a-ketoester is the first preparation of such metallic species in this series. It was obtained from the reaction between the /1-iodo-a-ketoester precursor 16 and magnesium. In this case, the form of the metal is critical and magnesium powder with a large surface area is necessary (equation 6). 

In spite of its formal similarity to the above mentioned annulation processes, the reaction shown in 4.37. includes a unique migration step. Oxidative insertion of the palladium into the phenyl-iodine bond is followed by the migration of the palladium onto the more electron rich indole ring. The 2-indolylpalladium complex than carbopalladates the pendant alkync moiety and the process ends by the formal activation of a C-H bond of the phenyl substituent and subsequent reductive elimination, furnishing the pentacyclic product.48 The same strategy has been utilised in the preparation of the indoloindolone framework from /V-bcnzoyl-3-(o-iodophcnyl)-indolc in an oxidative addition - palladium migration - C-H activation sequence.49... 

Although there are a few examples of iodine bonded only to carbon ligands, most complexes contain other, more electronegative ligands in the coordination sphere. There are few examples of chlorine and bromine complexes, and, as yet, no examples even with iodine of oxidation state VII. Most of these complexes, and especially the more stable examples, have aromatic... 

Let us now look at some examples to illustrate what we have discussed so far to get a feeling of how structural moieties influence the mechanisms, and to see some rates of nucleophilic substitution reactions of halogenated hydrocarbons in the environment. Table 13.6 summarizes the (neutral) hydrolysis half-lives of various mono-halogenated compounds at 25°C. We can see that, as anticipated, for a given type of compound, the carbon-bromine and carbon-iodine bonds hydrolyze fastest, about 1-2 orders of magnitude faster than the carbon-chlorine bond. Furthermore, we note that for the compounds of interest to us, SN1 or SN2 hydrolysis of carbon-fluorine bonds is likely to be too slow to be of great environmental significance. 

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