Insertion involving carbonyls

A 1,3-oxathiolane derivative (100) is formed when 2-mercaptoethanol is carbonylated by nickel carbonyl in pyridine (Scheme 118).181 It is probable that the mechanism involves carbonyl insertion into the Ni—S bond of intermediate thiolatonickel complexes and it is significant that compounds in this category (cf. 101,102) can be transformed into the cyclic thiocarbonate by treatment with carbon monoxide (Scheme 118).181... 

This route probably involves carbonyl insertion into a metal-carbene bond. Closely related compounds can also be prepared from M(CO)g (M = Cr, W)-a-lithiated sulfides-[Et3 0][Bp4] or by treatment of pentacarbonyl(thio)metal complexes,... 

Carbon monoxide insertion reactions in hydrocarbyl complexes of group VIII are particularly relevant because several industrial processes involving carbonylation of an organic substrate are catalyzed by metals belonging to this group. In the subsections that follow, reference to catalytic processes is made on each specific occasion. 

The following steps are involved in the proposed mechanism (i) oxidative addition of hydrosilane to the rhodium(I) complex (25) to give 26 (ii) insertion of carbonyl into the resulting silicon-rhodium bond of 26 to form a diastereomeric a-siloxyalkylrhodium hydride intermediate (28) (iii) formation of an optically active silyl ether of the sec-alcohol by reductive elimination, as shown in equation 75. 

Reactions involving the modification of ligands These reactions modify the present ligands, without adding or removing any. These include insertion reactions, carbonyl insertions (also known as alkyl migration), hydride elimination, and abstraction. 

The indenone 70 is obtained by the reaction of o-iodobenzaldehyde (66) with alkyne [22,23], Two mechanisms are suggested. One of them involves the formation of Pd(IV) species 68 from 67 by oxidative addition of aldehyde, and its reductive elimination affords the indenone 70. Another possibility is the insertion of carbonyl group (or nucleophilic attack) to form the indenyloxypalladium 69, and /i-H elimination gives the indenone 70. 

Other classes of nickel-catalyzed [3+2] cycloadditions include the addition of 2-haloacetophenone derivatives to alkynes to produce indenol derivatives (Scheme 3-36). This process likely involves initial oxidative addition to the haloaromatic, followed by alkyne insertion and carbonyl addition. In this case, zinc powder serves as reducing agent to regenerate the active nickel(0) catalyst. A mechanistically intriguing cycloaddition that proceeds without the action of reducing agents is the direct formation of bicyclic products from the addition of unsaturated ketones with alkynes. This process likely involves initial metallacycle formation followed by unusual rearrangement steps unique to the requisite doubly unsaturated carbonyl component. 

When alkyl-substituted carbonyl complexes are photolyzed, reactions other than ligand substitution can occur. One such reaction is the migratory insertion reaction that involves carbonylation of an alkyl complex to give an acyl product. Thus when MnCH3(CO)5 is photolyzed in an argon matrix at 17 K, the 5-coordinate acetyl complex Mn(COCH3)(CO)4 formed by migratory insertion is observed ... 

Conceptually similar palladium-catalyzed cascade reactions have been developed, involving molecular-queuing cycloaddition, cyclocondensation and Diels-Alder reactions [71], cydization-anion-capture-olefin metathesis [72], carbonylation-allene insertion [73], carbonylation/amination/Michael addition [74], sequential Petasis reaction/palladium-catalyzed process [75], supported allenes as substrates [76], and palladium-ruthenium catalysts [77]. 

The product (6 hexanohde) is a cyclic ester or lactone (Section 19 15) Like the Baeyer-Vilhger oxidation an oxygen atom is inserted between the carbonyl group and a carbon attached to it But peroxy acids are not involved m any way the oxidation of cyclohexanone is catalyzed by an enzyme called cyclohexanone monooxygenase with the aid of certain coenzymes... 

Cobalt carbonyl complexes involving InBr form when InBr inserts into the Co—Co bond in CojtCoJg ... 

The chemical reactivity of the organoruthenium and -osmium porphyrin complexes varies considerably, with some complexes (M(Por)R2, M(Por)R and Os(OEP)(NO)R) at least moderately air stable, while most are light sensitive and Stability is improved by handling them in the dark. Chemical transformations directly involving the methyl group have been observed for Ru(TTP) NO)Me, which inserts SO2 to form Ru(TTP)(N0) 0S(0)Me and Ru(OEP)Me which undergoes H- atom abstraction reactions with the radical trap TEMPO in benzene solution to yield Ru(OEP)(CO)(TEMPO). Isotope labeling studies indicate that the carbonyl carbon atom is derived from the methyl carbon atom. "" Reaction of... 

The insertion of a carbonyl group into a metal-alkyl or metal-aryl bond, and the reverse reaction involving decarbonylation of an acyl complex, have been studied from both the synthetic and mechanistic points of view. The mechanism proposed for this type of reaction seems well established and is... 

Carbon monoxide insertion into Ni—C bonds has been postulated in carbonylation reactions involving (7r-C3H5NiX)2 (X = C1, Br, or I) (112, 123a). 

After the precatalyst is completely converted to the active catalyst Xq, three steps are required to form the desired reduction product. The first step is the coordination of dehydroamino acid (A) to the rhodium atom forming adducts (Xi) and (Xi ) through C=C as well as the protecting group carbonyl. The next step is the oxidative addition of hydrogen to form the intermediate (X2). The insertion of solvent (B) is the third step, removing the product (P) from X2 and regenerating Xq. Hence, the establishment of the kinetic model involves these three irreversible steps. 

As corroborated by deuterium labeling studies, the catalytic mechanism likely involves oxidative dimerization of acetylene to form a rhodacyclopen-tadiene [113] followed by carbonyl insertion [114,115]. Protonolytic cleavage of the resulting oxarhodacycloheptadiene by the Bronsted acid co-catalyst gives rise to a vinyl rhodium carboxylate, which upon hydrogenolysis through a six-centered transition structure and subsequent C - H reductive elimina-... 

In 1975 Demerseman and co-workers reported two new preparations for Cp2Ti(CO)2 via the reductive carbonylation of Cp2TiCl2. The first of these involved the reaction of either Cp2TiCl2 or (Cp2TiCl)2 with AlEt3 in a CO atmosphere. After these heptane suspensions or benzene solutions were stirred for 20 hours at 20°C, Cp2Ti(CO)2 (1) could be isolated in 30% yield (26). No speculation as to the mechanism of this reduction was discussed however, alkylation and CO insertion steps are probably involved. 

Carbonyl insertion is preferentially observed in the photoindueed reaction of 22 to give the cyclohexenones 25 and 26 as shown in Scheme 9 [17]. The acyl complex 24 is involved as an intermediate. The eyclohexenone formation appears to be susceptible to conformational effect, as observed in the facile rearrangement of 27 to 28. 

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