Halogenation addition complexes

In addition to halogen bonded complexes or ionic salts, it is also possible for sulfur and selenium electron donors to form complexes in which the electron donor atom inserts into the X2 bond, giving a hypervalent donor atom with a T-shaped geometry. It has been recently reported [147] that for dibromine and selenium, this type of complex is favored over halogen bonded complexes. While no purely halogen bonded complex is reported for dibromine, there is one complex (IRABEI) in which one selenium atom of each of several selenanthrene molecules in the asymmetric unit does insert into a Br2 bond, but for one of the molecules, the other selenium atom forms a halogen bond with a Br2 molecule to form a simple adduct (A). 

The simplest modification occurs on addition of nucleophilic anions X to Lewis acids MX , resulting in the creation of an ate-complex as anionic adduct (Table 11) (reaction 162). The formation of complex anions can also be the result of halogen addition, with the formation of mixed or symmetrical trihalides [YX2], or else of hydracid addition, with formation of anions [XHY]-, which are not very stable and readily dissociated in solution but are characterizable in the solid state (reaction 163). 

Their utility has been demonstrated in various Friedel-Crafts reactions,44-47 halogen addition,48 49 electrophilic nitration of aromatics,50 and various hydrogenation processes51-53 including the Ru-catalyzed hydrogenation of C02 to /V,/V-dipropyl formamide in supercritical C02 under biphasic conditions 54 The use of in situ IR spectroscopy allowed Horvath and coworkers to demonstrate that the same substrate-catalyst and product-catalyst complexes are produced in Friedel-Crafts acetylation of benzene in ionic liquids as in CH2C12 55... 

Halogenation of complex XXII afforded a mixture of 2-endo-methoxy-6-halo-ds-bicyclo[3.3.0]octane epimers, XXIVa and XXIVb (Table VI). In methanol, 2,6-endo,endo-dimethoxy-cis-bicyclo [3.3.0] octane, XXV, was obtained in addition to XXIV. The presence of halide ions suppressed the formation of XXII and favored that of XXIVb. Control experiments showed that both XXIV and XXV were primary products and did not... 

There have been both experimental and theoretical studies to probe the degree of concertedness in gas-phase substitutions as shown in Scheme 1. Is (2) an intermediate with a finite lifetime, or are the addition and elimination steps concerted so that (2) is a transition state Experimental molecular beam studies on the femtosecond time-scale have been reported for the reaction of chloride ions with the iodobenzene cation to yield chlorobenzene and iodine. The results show an 880 fs reaction time for the elimination process, indicating a highly non-concerted process, so that here the er-complex is an intermediate rather than a transition state.12 The reactions of halobenzene cations with ammonia have been interpreted in terms of the formation of an addition complex which may eliminate either halogen, X, or hydrogen halide, HX, depending on the nature of the halogen.13... 

Electron depopulation of the donor and concomitant population of the acceptor in the complex results in a lowering of the vibrational frequencies in the IR spectra of the donor and acceptor moieties. Additionally, complex formation can decrease the symmetry of the donor/ acceptor dyad and can lead to increased IR intensity or the appearance of new bands. For example, in halogen/alkylbenzene complexes, the stretching frequencies of the halogens are lowered, as seen in the shift of chlorine band from 557 cm-1 in free chlorine to 530 cm-1 in the benzene complex, to 527 cm-1 in the toluene complex, and to 524 cm-1 in the p-xylene complex. Increases in the intensity of some of the arene bands are also clearly seen [23b]. 

The ene-type chlorination, specific with this halogen atom, of alkenes would account for a somewhat different mode of halogen addition, giving useful allylic chlorides. Efficient and convenient reagents and methods developed are dichlorine monoxide (CI2O equation 36), r-butyl hypochlorite, and electrochemical reactions with chloride ion (equation 37). llie ene-type chlorination proceeds smoothly with 1,1-disubstituted alkenes (74) and (76) to give (75) and (77). Especially, dichlorine monoxide is a potential reagent for complex molecules such as penicillin and cephalosporin derivatives. ... 

The reader is referred to Pryde (86) for a more thorough discussion on the kinetics of autoxidation of phospholipids their forming metal ion, iodine, and other complexes halogen addition and their behavior during hydration, hydrogenation (with heterogeneous and homogeneous catalysts), hydrolysis and alcoholysis, hydroxylation, oxidation, radical, and other reactions. 

Co Halogen containing complex phosphine chelate Addition of water Ethanol [15]... 

In the case of reaction (j), the cationic product is converted to M(CO)2( >-triars)X2 by recrystallization from hot methanol (M = Mo, only). Other examples of halogen addition exist for Mo and W carbonyl complexes that contain N-donor ,P-donor " S and As-donor ligands. 

The ease in replacing halogen in halogenonitrobenzenes is, in all probability, due to the activity of the nitro group in forming addition complexes. Garner and Gillbe have shown that dinitrobenzene forms addition complexes with ammonia that show measurable conductivities. ... 

Each trihalide may be made (although not necessarily most conveniently) by direct union of the elements. They will easily undergo atmospheric oxidation to the oxyhalide, add sulphur to form the thiohalide, hydrolyse under acid conditions to form phosphorous acid, readily add more halogen to form the pentahalide, and form addition complexes with various metals. 

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