Carbonyl pseudohalides

Phosgene can be used as the starting material for the preparation of other potentially useful carbonyl halides and carbonyl pseudohalides. Reaction of phosgene with fluorspar, for example, gives COCIF (see Section 9.1.1 and Chapter 16). With aluminium(III) bromide, COBrj is formed (Section 9.1.2.6). Reaction of COClj with HF gives COFj (see Section 9.10.4 and Chapter 13), reaction with silver cyanide gives carbonyl dicyanide, CO(CN)j (Section 9.1.7), whereas reaction with a mixture of sodium fluoride and HCN gives the mixed carbonyl halide pseudohalide, COFCN (Section 9.1.7 and Chapter 13). The chemistry of these... 

The so-called "ene" reaction has not been observed with phosgene, although it occurs readily with the related carbonyl pseudohalide, CO(CN)j [972]. Moreover, no Diels-Alder product is obtained when 1,3-cyclohexadiene is reacted with phosgene. Acyl chlorides are formed at 80 C and very high pressures, but no reaction occurs between 1,3-cyclohexadiene and COCl, at atmospheric pressure [1185]. 

The palladium-catalyzed Heck carbonylation reaction is a powerful means of generating amides, esters, and carboxylic acids from aryl halides or pseudohalides [28]. The development of rapid, reliable, and convenient procedures for the introduction of carbonyl groups is important for the development of high throughput chemistry in general and high-speed microwave-mediated chemistry in particular. Unfortunately, the traditional method of introducing carbon monoxide into a reaction mixture via a balloon or gas tube is not practical because of the special requirements of microwave synthesis. 

It has been recently reported that an organic pseudohalide can function as a promoter in the methanol carbonylation reaction. Webber et al. (21) have shown that pentachlorobenzenethiol will promote the rhodium-catalyzed reaction but at less than 5% of the rate of the iodide system. 

Scheme 5. Palladium-catalyzed carbonylations of aryl halides and pseudohalides...

Protection of carbonyl groups. A number of organosilicon pseudohalides (e.g., Me3SiX X-CH, SR, N3 etc.) have been shown to add to carbonyl groups, especially in the presence of suitable catalysts. 

Z. Iqbal Intra- and Inter-Molecular Bonding and Structure of Inorganic Pseudohalides with Triatomic Groupings. P.S.Braterman Spectra and Bonding in Metal Carbonyls. Part A Bonding... 

Lever has successfully predicted Mn"/ potentials of 24 Mn-carbonyl complexes containing halide, pseudohalide, isonitrile, and phosphine co-ligands, with additivity parameters derived from the potentials of Ru "/" couples [39]. An important consideration for heteroleptic complexes is the influence of isomerism on redox thermodynamics. For Mn(CO) (CNR)6- complexes, with n = 2 or 3, the Mn"/ potentials for cis/trans and fac/mer pairs differ by as much as 0.2 V [40]. The effect arises from the different a-donor and 7r-acceptor abilities of carbonyl (CO) and isocyanide and their influence on the energy of the highest energy occupied molecular orbital (HOMO). 

In addition to halides, some pseudohalides undergo facile oxidative addition to Pd and Ni complexes. Trifluoromethanesulfonates (triflates), namely aiyl triflates 3 derived from phenols and enol triflates of carbonyl compounds, are most useful. 

Alkenyl halides and their pseudohalides also react with Pd(0) to form the alkenylpalladium intermediates 11, and their transformations are summarized in Scheme 3.4. In addition to alkenyl halides, the enol triflates 12 undergo oxidative addition, showing that carbonyl compounds are useful starting compounds for Pd-catalysed reactions. 

Other pseudohalides are carbonylated. Benzoic acid derivatives are prepared from arenediazonium salts at room temperature without addition of a phosphine ligand [223], For example, the acid anhydride 457 is prepared by the carbonylation of the benzenediazonium salt 456 in the presence of AcONa. By this method, nitrobenzene can be converted to benzoic acid indirectly. 

There have been no successful syntheses using carbonylate anions with halide or pseudohalide substituents. Indeed, it is known that cyanide-containing anions react with organosilicon halides to give isonitrile derivatives (50), e.g.,... 

For the ketone synthesis via the present protocol, acid chlorides are useful precursors, in deed. Nevertheless, carbonylative cross coupling with organic halides is strategically the most simple and direct way to this purpose. The palladium-catalyzed carbonylative cross-coupling reaction with various organic halides has been extensively investigated, because of its merits from synthetic as well as phenomenal point of view. Acid chlorides are not always readily available, and their preparation is not always compatible with many sensitive functionalities. Therefore the development of this type of reaction widens the scope of the ketone synthesis in the present protocol because of the ready availability and storability of organic halides and pseudohalides. 

The arena of mononuclear carbonyl complexes of iridium is dominated by Vaska s compound, [IrCl(CO)(PPh3)2] (29), and its variants. The most conunon variation found in the literature comes from replacement of the chloride ligand with other monoanionic hgands such as halides and pseudohalides. Infrared spectroscopy has been used (by examining... 

The best nucleophiles for the SrnI mechanism can make a relatively stable radical in the initiation part, either by resonance (enolates) or by placing the radical on a heavy element (second-row or heavier nucleophiles). The best electrophiles for the SrnI mechanism are able to delocalize the odd electron in the radical anion (aromatic leaving groups, carbonyl compounds), can make a stable radical (3° alkyl halides), and have a weak R-X (Br, I) bond. Tosylates and other pseudohalides are very poor SrnI electrophiles. If light is required for substitution to occur, the mechanism is almost certainly SrnI. 

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