Acyl from carbonyl complexes

Mononuclear acyl Co carbonyl complexes ROC(0)Co(CO)4 result from reaction of Co2(CO)8 with RO-.77 These also form via the carbonylation of the alkyl precursor. The ROC(0)Co(CO)4 species undergo a range of reactions, including CO ligand substitution (by phosphines, for example), decarbonylation to the alkyl species, isomerization, and reactions of the coordinated acyl group involving either nucleophilic attack at the C or electrophilic attack at the O atom. 

From Acyl Complexes Generated from Carbonyl Complexes... 

Formation of metal acyl or carbonyl complexes from 1-alkynes in the presence of water is often assumed to proceed via attack on an intermediate vinylidene complex to give a hydroxycarbene complex (Equation 1.24) ... 

Many industrially important catalytic processes use alkyl and acyl cobalt carbonyl complexes, which can be synthesized from (2 ). Acyl complexes produced after formation of... 

In contrast, acyl metal carbonylate complexes of Fe and Ni are highly reactive at the metal center and can be used in organic transformations where intermediates arising from nucleophilic attack by the metal on the organic substrate are involved. These acyl anions have much of the negative charge on the metal atom. 

Subsequent insertion of CO into the newly formed alkyl-ruthenium moiety, C, to form Ru-acyl, D, is in agreement with our 13C tracer studies (e.g., Table III, eq. 3), while reductive elimination of propionyl iodide from D, accompanied by immediate hydrolysis of the acyl iodide (3,14) to propionic acid product, would complete the catalytic cycle and regenerate the original ruthenium carbonyl complex. 

Zirconium hydride reactivity with carbon monoxide demonstrates the strong driving force toward products with a Zr-O bond. Indeed, the facility of the CO migratory insertion into Zr-C and especially Zr-H bonds may be from a carbonyl oxygen-zirconium interaction that stabilizes the transition state to the acyl and formyl complexes. 

The fact that there is such a paucity of metal formyl complexes is both interesting and significant because of the proposed intermediacy of coordinated formyl in CO reduction, and the sharply contrasting abundance of metal acyl complexes. Since many of the acyl complexes are known to form by migratory insertion of CO in an alkyl carbonyl complex (20, 20a, 22), the lack of formyl complexes from hydride carbonyls relates to the thermodynamic difference in the equilibrium (5) when Y is alkyl and when it is hydride. 

The hydroacylation of olefins with aldehydes is one of the most promising transformations using a transition metal-catalyzed C-H bond activation process [1-4]. It is, furthermore, a potentially environmentally-friendly reaction because the resulting ketones are made from the whole atoms of reactants (aldehydes and olefins), i.e. it is atom-economic [5]. A key intermediate in hydroacylation is a acyl metal hydride generated from the oxidative addition of a transition metal into the C-H bond of the aldehyde. This intermediate can undergo the hydrometalation ofthe olefin followed by reductive elimination to give a ketone or the undesired decarbonyla-tion, driven by the stability of a metal carbonyl complex as outlined in Scheme 1. 

Palladium-catalyzed ketone synthesis B. The reaction mixture is saturated with carbon monoxide, which intervenes in step 2 by forming a palladium(II) carbonyl complex. Before the transmetalation (above referred to as step 3) takes place a rearrangement is interposed. The ligand Rmisa rji cd undergoes a [l,2]-shift from Pd(II) to the carbon atom of carbon monoxide, leading to the formation of an acylpalladium(II) complex with the structure P lllsa llra cd-(C=0)-Pd(-X) L j. With regard to the above-mentioned steps 3-4 it behaves like the acyl-Pd(II) complex of the ketone synthesis A and, after reductive elimination, i.e. in step 5, yields... 

Water also attacks the electrophilic a carbon of the ruthenium vi-nylidene complex 80. The reaction does not yield the ruthenium acyl complex, however, as is found for the reaction with the similar iron vinylidene complex [(i75-C5H5)(CO)2Fe=C=CHPh]+ (56), but rather 91 is the only isolated product (78). The mechanism for this transformation most reasonably involves rapid loss of H+ from the initially formed hydroxycarbene to generate an intermediate acyl complex (90). Reversible loss of triphenyl-phosphine relieves steric strain at the congested ruthenium center, and eventual irreversible migration of the benzyl fragment to the metal leads to formation of the more stable carbonyl complex (91) [Eq. (86)]. 

By reaction of cationic carbonyl complexes with lithium carbanions, neutral acyl complexes are prepared. Whereas treatment of [> -CpFe(CO)3]BF4 with (a) PhLi gives the expected > -CpFe(CO)2 [C(0)Ph] in 80% yield, with (b) MeLi only traces of > -CpFe(CO)2 [C(0)Me] can be detected . This complex and other phosphane-substituted acyl compounds of the type f -CpM(CO)L[C(0)Me] [M = Fe, Ru L = CO, PPh3, P(hex)j], as well as >/ -CpMo(CO)2P(hex)3[C(0)Me] (prepared by different routes), are protonated with and alkylated with [R3 0]BF4 reversibly, yielding cationic hydroxy- and alkoxy(methyl)carbene complexes, respectively . The formation of the ( + )- and ( —)-acetyl complex / -CpFe(C0)(PPh3)[C(0)Me] from the ( + )-and ( —)-conformers of optically active > -CpFe(C0XPPh3)[C(0)0-menthyl] and MeLi occurs with inversion of configuration at the asymmetric iron atom . 

Whilst reaction of acyl chloride 303 with Na[Co(CO)3(PEt3)] affords the oxocyclobut-enyl complex 306" by ring expansion and CO loss, analogous treatment with NaRe(CO)5 delivers the non-fluxional // -cyclopropenylrhenium compound 305" . In the latter case, compound 304 loses carbon monoxide with concomitant migration of the cyclopropenyl moiety from carbonyl to rhenium as an allylic rearrangement rather than a 1,2-shift. 

BP extended this Ir carbonylation chemistry with the discovery of proprietary promoters to achieve commercially viable high reaction rates at low reaction water conditions with essentially no dependence of CO partial pressure on the reaction rate [20]. These promoters can be categorized in two groups simple iodide complexes of Zn, Cd, Hg, Ga, and In or carbonyl complexes of Re, Ru, Os, or W. It is believed these promoters participate in the rate-determining step to abstract iodide from [Ir(CH3)(CO)2(I)3] , thus facilitating methyl migration to form the corresponding acyl complex, [Ir(CH3)(CO)2 (1)3]-. 

The value of the metal complexation results from control of the reaction, rather than any activation, Lewis acids being excellent catalysts for diene polymerization. Friedel-Crafts acylations of diene complexes have been used for the preparation of dienes, with decomplexation following carbonyl reduc-tion. 5 Decomplexation to afford dienones has been less explored. The intermediate cationic o -complex on treatment with triethyl phosphite or triphenylphosphine affords metal-free. y-unsaturated phospho-nates or phosphonium salts (Scheme 19). The initial s-cis conformation of the diene fragment of the... 

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