Monoxide double insertion

Insertions of isocyanide into niobium-carbon bonds follow a path similar to that with vanadium, resulting in the formation of the 7]2-iminoacyl complexes, which can then be involved in further chemistry.175 176 The reaction of acetone with cyclopentadienyl complex 110 under a carbon monoxide atmosphere gives the if -acetone compound 111. Complex 111 subsequently undergoes either stepwise insertion of two isocyanides via 112 or double insertion of the isocyanide to give complex 113 (Scheme 48).177... 

A double insertion of carbon monoxide has been observed for the amine-induced reaction of alkynes with dodecacarbonyltriiron leading to cydobutenediones (Scheme 1.7) [28]. 

Reactions of monomeric and dimeric rhodium(II) porphyrins with carbon monoxide - As already reported in Sect. 3.3, a carbonylrhodium(II) porphyrin behaves as an acyl radical. Hence, if possible, dimerization or coupling reactions occur. Evidence for the formation of isomeric 2 1 Rh(P) CO adducts, namely a monoadduct of the dimer and a metallo ketone complex, and a dimeric 1 1 adduct in the reaction of [Rh(OEP)]2 with carbon monoxide according to sequences (38) and (39) has been presented [340,341] solution equilibria and structures have been studied essentially by lHNMR, 13CNMR, and IR spectroscopy. The first half of sequence (38) and reaction (39) occurred in parallel at CO pressures up to 12 atm at 297 K. At higher pressures, or at lower temperatures, the double-insertion of CO shown in the last step of (38) was observed. 

Under conditions similar to those for allyl halides, 1,4-dichlorobutene reacts with nickel carbonyl to give butadiene. However, a double insertion of acetylene and carbon monoxide can be successfully carried out using 4-chloro-2-buten-l-ol and generating hydrogen halide in situ with a weak acid inorganic halide combination, e.g., NaBr-H3P04 (58). 

Sm(II) mediated formation of very sophisticated chelating ligands has been observed. The powerful reducing agent CpJSm can induce facile double bond insertion of CO into C=C and C=N double bonds (Eq. 13) [176]. Carbon monoxide also inserts into the Y-pyridyl bond of CpfY(2-pyridyl) to form a bridging /i-f/2 >/2-dipyridyl ketone fragment (Eq. 14) [177]. 

Samarium-mediated functionalization also occurs in the case of N=N bonds [287]. A high yield (80%) double insertion of carbon monoxide into the N=N... 

Double insertions of carbon monoxide into the same metal-hydrocarbyl bond [reaction (j)], are doubtful and multiple insertions [reaction (k)] are unknown. This should be attributed to the relatively lower strength of the carbon-carbon bond in a sequence of the type —C(0)—C(0)—, as shown by the available bond energy data . For example, while the carbon-carbon bond strength in ethane is 376 kJ/mol, the corresponding value in MeC(O)—C(0)Me has been evaluated to be 282 kJ/mol... 

The product of the formal double insertion of carbon monoxide [reaction (j)] occurs in the case of a-bromophenylethane. 

Unusual metaloxyketene thorium complexes have been prepared via double insertion of carbon monoxide into thorium-silicon bonds (Scheme 42). In the structure of Gp 2Th(Cl)[0C(=C=0)Si(SiMe3)3] the ketene unit is oriented roughly in the plane bisecting the Cp rings. The Th-Cl and Th-O bond distances are 2.651(5) and 2.15(1) A respectively.106... 

Radu NS, Engeler MP, Gerlach CP, Tilley TD, Rheingold AL (1995) Isolation of the first d metalloxy ketene complexes via double insertion of carbon monoxide into thorium-silicon... 

The thermal benzannulation of Group 6 carbene complexes with alkynes (the Dotz reaction) is highly developed and has been used extensively in synthesis [90,91]. It is thought to proceed through a chromium vinylketene intermediate generated by sequential insertion of the alkyne followed by carbon monoxide into the chromium-carbene-carbon double bond [92]. The realization that photodriven CO insertion into Z-dienylcarbene complexes should generate the same vinylketene intermediate led to the development of a photochemical variant of the Dotz reaction (Table 14). 

Cyclopentanones form from CO and double bonds in 1,5-positions (example 43, Table VII). This is a very selective and stereoselective process, the 1,4- or 1,6-positions being not significantly reactive under the same conditions. o-Hydroxyphenylacetylenes also form 5-membered lactones (example 45, Table VII). In some cases ring closure leads to a new nickel-carbon bond into which a new molecule of carbon monoxide can be inserted. This process of alternative insertion of carbon monoxide and other unsaturated ligands can be repeated several times so that complex alicyclic structures can be formed (example 49, Table VII). This... 

Allyl methylcarbonate reacts with norbornene following a ruthenium-catalyzed carbonylative cyclization under carbon monoxide pressure to give cyclopentenone derivatives 12 (Scheme 4).32 Catalyst loading, amine and CO pressure have been optimized to give the cyclopentenone compound in 80% yield and a total control of the stereoselectivity (exo 100%). Aromatic or bidentate amines inhibit the reaction certainly by a too strong interaction with ruthenium. A plausible mechanism is proposed. Stereoselective CM-carboruthenation of norbornene with allyl-ruthenium complex 13 followed by carbon monoxide insertion generates an acylruthenium intermediate 15. Intramolecular carboruthenation and /3-hydride elimination of 16 afford the -olefin 17. Isomerization of the double bond under experimental conditions allows formation of the cyclopentenone derivative 12. 

Transmetallation of silyl enol ethers of ketones and aldehydes with Pd(II) generates Pd(II) enolates, which are usefull intermediates. Pd(II) enolates undergo alkene insertion and -elimination. The silyl enol ether of 5-hexen-2-one (241) was converted to the Pd enolate 242 by transmetallation with Pd(OAc)2, and 3-methyl-2-cyclopentenone (243) was obtained by intramolecular insertion of the double bond and -elimination [148], Formally this reaction can be regarded as carbopalladation of alkene with carbanion. Preparation of the stemodin intermediate 246 by the reaction of the silyl enol ether 245, obtained from 244, is one of the many applications [149]. Transmetallation and alkene insertion of the silyl enol ether 249, obtained from cyclopentadiene monoxide (247) via 248, afforded 250, which was converted to the prostaglandin intermediate 251 by further alkene insertion. In this case syn elimination from 250 is not possible [150]. However, there is a report that the reaction proceeds by oxypalladation of alkene, rather than transmetallation of silyl enol ether with Pd(OAc)2 [151]. 

Butadiene is carbonylated catalytically to form 3-pentenoate in the presence of palladium and hydrogen chloride in alcohol (16). In this reaction, butadiene forms an unsymmetrical 7r-allylic complex by the insertion of one of the double bonds into the palladium-hydrogen bond. Then the insertion of carbon monoxide takes place at the less hindered carbon of the complex to give 3-pentenoate. 

Chain propagation of CO/ethylene copolymerization proceeds by a strictly alternating insertion of CO and olefin monomers in the growing chain. It is safe to assume that double CO insertion does not occur for thermodynamic reasons [Ic]. However, the complete absence of double ethylene insertions is remarkable because ethylene insertion in a Pd-alkyl species must be exothermic by about 20 kcal/mol (84 kJ mol). The observation of strict alternation is the more surprising since the same palladium catalysts also efficiently dimerize ethylene to butenes [25]. The perfect alternation is maintained even in the presence of very low concentrations of carbon monoxide. When starting abatch polymerization at a high ethylene/CO ratio, error-free copolymer is produced until all the CO is consumed then the system starts forming butenes (with some catalyst systems at about twice the rate of copolymerization ). 

In summary, chain propagation involves alternating reversible carbon monoxide insertion in Pd-alkyl species and irreversible insertion of the olefin in the resulting Pd-acyl intermediates. The overall exothermicity of the polymerization is caused predominantly by the olefin insertion step. Internal coordination of the chain-end s carbonyl group of the intermediate Pd-alkyl species, together with CO/olefin competition, prevents double olefin insertion, and thermodynamics prevent double CO insertions. The architecture of the copolymer thus assists in its own formation, achieving a perfect chemoselectivity to alternating polyketone. 

Addition of carbon monoxide and water to an alkene, i.e. hydrocarboxylation, is catalyzed by a variety of transition metal complexes, including [Ni(CO)4], [Co2(CO)s] and [HaPtClg]. Unfortunately this reaction usually leads to mixtures of products due to both metal-catalyzed alkene isomerization and the occurrence of Irath Markownikov and anti-Markownikov addition of the metal hydride intermediate to the alkene. The commercially available zirconium hydride [(C5Hs)2Zr(H)Cl] can be used as a stoichiometric reagent for conversion of alkenes to carboxylic acids under mild conditions (equation 23). In this case the reaction with linear alkenes gives exclusively terminal alkyl complexes even if the alkene double bond is internal. Insertion of CO followed by oxidative hydrolysis then leads to linear carboxylic acids in very good yield. 

The double carbonylation has been suggested to occur via a primary carbon monoxide insertion of reaction (k), followed after the keto-enol equilibrium shown by reaction (1), by a second carbon monoxide insertion, [reaction (m)] into the cobalt-carbon bond of the a-hydroxyalkyl derivative. 

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