Carbonylation superelectrophilic

The enthalpy of fomation of two such species has been measured, namely the cyclopropane and cycloheptane derivatives. The difference between the values for these two species, both as solids, is 238.1 kJmol . Is this difference plausible Consider the difference between the enthalpies of formation of the parent cycloalkanes as solids, 194 kJ mol . The ca 44 kJ mol discrepancy between these two differences seems rather large. However, there are idiosyncracies associated with the enthalpies of formation of compounds with three-membered rings and almost nothing is known at all about the thermochemistry of compounds with seven-membered rings. Rather, we merely note that a seemingly well-defined synthesis of cycloheptyl methyl ketone was shown later to result in a mixture of methyl methylcyclohexyl ketones, and superelectrophilic carbonylation of cycloheptane resulted in the same products as methylcyclohexane, namely esters of 1-methylcyclohexanecarboxylic acid. The difference between the enthalpies of formation of the unsubstituted alicyclic hydrocarbons cycloheptane and methylcyclohexane as solids is 33 kJmol . This alternative structural assignment hereby corrects for most of the above 44 kJ mol discrepancy in the enthalpies of formation of the two oximes. More thermochemical measurements are needed, of oximes and cycloheptanes alike. 

Akhrem and co-workers417 have successfully applied aprotic organic superacids in the carbonylation of a series of alkanes. Butane was transformed into isomeric carboxylic acids depending on the superelectrophilic reagent and isolated as the... 

Olah et al.450 have recently described a new, highly efficient superelectrophilic formylation-rearrangementofisoalkanes. Branched ketones are formed in high yields and with high selectivity with no detectable branched acids (Koch products) in the presence of moderately strong superacids such as HF-BF3 or triflic acid-BF3. Carbonylation of isobutane under such conditions gives isopropyl methyl ketone in high yield [Eq. (5.164)] The transformation was interpreted with the involvement of... 

Knorr cyclization of a range of iV-susbtituted butyramides in triflic acid yields 4-methyl-17/-quinolin-2-one derivatives704 [Eq. (5.257)]. Suggested intermediates of the transformation directly observed by low-temperature multinuclear NMR spectroscopy (HSO3F SbF5 S02C1E, 40°C) are distonic superelectrophiles formed by diprotonation of the two carbonyl oxygen atoms. 

Another related class of gitonic superelectrophiles are the superelectrophilic halocarbonyl dications. The halocarbonyl cations (XCO+, X = F, Cl, Br, I) have been prepared under long-lived stable ion conditions and characterized by 13C NMR spectroscopy.68 Sommer and co-workers studied the bromine-assisted carbonylation of propane in superacids, and... 

It has been demonstrated that nitronic acids and a-carbonyl nitro-methanes can form superelectrophilic intermediates in strong acids and the resulting species are capable of reacting with benzene (eqs 65-67).23... 

It has been proposed that the gitonic superelectrophiles (217, 219, 221) arise from double protonation at the nitro group, and in the case of a-carbonyl nitromethanes (eqs 66-67), protonation also occurs at the carbonyl group to form highly reactive tricationic superelectrophiles (219 and 221). Because weaker acids are capable of forming the diprotonated species but do not lead to arylated products, tricationic reactive superelectrophiles are thought to be involved in limited equilibria concentrations. The dicationic species 218 can be directly observed by NMR spectroscopy. 

The conversion is thought to involve formation of the carboxonium ion (77) by protonation of the carbonyl oxygen, and subsequent protonation then occurs at the C-H bond. The resulting carboxonium-carbonium dication (78) possesses the maximum possible charge-charge separation for this bicyclic framework. Subsequently, an intermediate carboxonium-carbenium dication (79) is produced, which isomerizes to the tertiary -carbenium ion, and deprotonation provides the product enone (80). Similar distonic superelectrophiles are proposed in other rearrangements of terpenes in superacid.28... 

The resistance to cleavage is an indication of the superelectrophilic character of dication 150c. Several aromatic compounds have likewise been shown to produce dicationic species upon the protonation of carboxyl and carbonyl functional groups. Other bis-carboxonium dications have been described involving protonation of carbonyl, amide, and other groups.50 These distonic superelectrophiles (152-153) have been shown to be useful in condensation reactions (eqs 52-53). 

A homoleptic square-planar palladium(II) carbonyl complex [Pd(CO)4](Sb2Fii)2 that displays v(CO) at 2259 cm (the value for free CO is 2143 cm ) has been recently prepared. This is an exceptional complex, dubbed by the authors as superelectrophilic metal carbonyl . The very high value of v(CO) shows that the carbonyl hgands behave as a-donors (see Carbonyl Complexes of the Transition Metals). Additional data (e g. v(M )) and stability data support that this ligand is very weakly coordinated as only a a-donor. ... 

Metal carbonyls see Carbonyl Complexes of the Transition Metals) are extended to superelectrophilic cations, including square-planar [Pt(CO)4] + by reductive carbonylation of Pt(S03F)4 or PtFe in super acid environment (Scheme 12). Using a comparable approach, [Pt(CO)3] + in... 

Williams RJP (1983) Symbiotic chemistry of metals and proteins. Chem Br 17 1009-1013 Williams RJP (1986) Missing information in bio-inorganic chemistry. Coord Chem Rev 79 175-193 Williams RJP, Erausto Da SUva JJR (1996) The natural selection of the chemical elements. Clarendon, Oxford WiUner H, Aubke E (2002) Metal carbonyl cations and their derivatives - a new class of superelectrophiles. In Meyer G, Naumann D, Wesemann L (eds) Inorganic chemistry highlights. WUey-VCH, Weinheim... 

Scheme 5.9 Superelectrophilic activation of a,P-unsaturated carbonyl compounds...

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