Halogeno carbonyls

The use of a reagent bearing a basic center or the addition of a base to the reaction mixture was recognized as necessary to prevent the acid-catalyzed elimination of the elements of water from the intermediates. Since the publication of this work, a number of similar intermediates have been isolated from thioamides and a-halogeno carbonyl compounds (608, 609, 619, 739, 754, 801), and as a result of kinetic studies, the exact mechanism of this reaction has been well established (739, 821). 

Rhodium(i).—Group VII Donors. Halogeno-carbonyl and -phosphine complexes. Convenient atmospheric pressure syntheses have been reported for the complexes [RhCI(PF3)2]2 and [Rh(acac)2(PF3)2], by replacing olefins from suitable substrate complexes, e.g. 

It is deduced from infrared data (206) that iron pentacarbonyl reacts with bromine at — 80° C to form the cationic halogeno carbonyl [Fe(CO)sBr]+Br (206), and the covalent Br—CO—Fe(CO)4Br. From similar infrared data, however, it is concluded that the product is a seven-coordinate non-ionic complex Fe(CO)5Br2 (76) The reaction of Os(CO)3(PPh3)2 with hydrogen chloride produces a cationic hydrido carbonyl, which may be isolated, although it readily reverts to a neutral dichloride by attack of the associated chloride anion (52). 

Osmium(n).—Group VII Donors. Hydrido- and halogeno-carbonyl complexes. Carbonylation of [OsHX(CO)(PCy3)2] has produced the novel dicarbonyl hydride [OsHX(CO)2(PCy3)2] (X = Cl or Br Cy = tricyclohexyl).17 I.r. and n.m.r. data indicate the geometry (17). Addition of other ligands to the five-co-ordinate... 

TABLE II.3 PYRAZINES PREPARED BY AMMONOLYSIS OF a-HALOGENO CARBONYL COMPOUNDS... 

Detailed discussion of the preparation of a variety of alkyl- and arylpyrazines by primary syntheses, principally from aliphatic components, appears in Chapter II. These include, for example, the preparation of 2,5-disubstituted and 2,3,5,6-tetrasubstituted alkyl- and arylpyrazines from a-amino carbonyl compounds, which may be produced by many methods such as reduction of a-hydroxyimino carbonyl compounds, aminolysis of a-halogeno carbonyl compounds, oxidation of a-amino... 

Halogeno-carbonyl and -phosphine Complexes. In an attempt to measure the charge distribution in complexes, the dipole moments of a number of complexes have been collected and group moments assigned. ... 

Halogeno-carbonyl and -phosphine complexes. I.r. spectral studies at elevated CO pressures have indicated that carbon monoxide, like other Lewis bases, is capable of bridge splitting in rhodium dicarbonyl halides, as in reaction (15). ... 

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