Acetyl complex

The a-alkoxy-substituted iron-acyl complex 8 is prepared by oxidation of the enolate prepared from iron-acetyl complex 6 and subsequent etherification12. 

I.3.4.2.5.I.2. Aldol Additions of Enolates of Chiral Iron-Acetyl Complexes... 

A third type of reaction, namely CO insertion, is also described. The rate of CO insertion into the Pd-Me bond in several classical diphosphine monomers has been found to be very dependent on the nature of the ligand. Full car-bonylation of, for example, dendrimer 56-[GJ occurs when this compound is pressurized to 1 bar of CO. Experiments with 13CO corroborate the formation of the acetyl complex while insertion of norbornene into the Pd-acetyl bond can be easily performed. Dendrimers of generations 2 and 3 react similarly (Scheme 27). 

Alkylation of an anionic acylmetallate is the second step in the classic Fischer synthesis of carbene complexes. The same type of reaction can be performed with stable neutral acyl complexes, producing cationic carbene compounds. Compound 17 has been prepared from a ruthenium acetyl complex by direct methylation and by protonation with subsequent methylenation (45) ... 

In the carbonylation of MeOH in the presence of Rh-exchanged zeolites, the Rhm ions are reduced to Rh1 ions, which lead to Rh-dicarbonyl and Rh-carbonyl-acetyl complexes.29-32 IrY and RhY zeolites catalyze the carbonylation of MeOH in the presence of a Mel promoter. The kinetics have been determined and IR spectra suggested that with the Ir catalyst the ratedetermining step was the addition of MeOH to the active species followed by migration of a Me coordinated to Ir. With the Rh catalyst, oxidative addition of Mel was the rate-determining step.33 A series of EXAFS measurements was made to determine the structural basis for... 

Because salts of the [Rh(CO)2X2] ion are not only simple to prepare but rather stable species under ambient conditions, the reaction of [Rh(CO)2X2] ions with methyl iodide can be readily studied. Infrared spectroscopy at room temperature (15) reveals that an acetyl complex of rhodium(III) is the first detectable species after reaction. This species was isolated as its trimethylphenylammonium salt, and the structure of this material has been determined by X-ray crystallography (16). The... 

The observation of extremely facile formation of an acetyl complex and the finding that oxidative addition is the rate-determining step are almost certainly related to the high selectivity observed in the reaction. Thus, the extremely short lifetime of any CH3—Rh species makes it unlikely that it would be reacted off to methane in the presence of hydrogen (and/or metal hydrides). 

The differences in products (both gaseous and in solution) between the reduction of the acetyl complex, CH3C(0)FeCp(C0)2, and the methyl and ethyl complexes suggest that different intermediates are involved. The rapidity of the reduction of the acetyl complex to hydrocarbons rules out the ethyl complex as an intermediate in the reduction of CH3C(0)FeCp(C0)2 with LAH. Reduction of the acetyl to the ethyl complex has been observed.1—... 

Reduction of transition metal acetyl complexes to ethyl complexes with BHa has been previously observed.19... 

We synthesized cationic y2-acetyl compounds 28,25 by combining iron acetyl complexes CpFe(C0)L(C0CH3) (g7) [L=C0,PPh3] with a coordinatively unsaturated (16-electron) metal carbonyl salt CpM(CO)n+[M=Fe,n=2 M=Mo,n=3], as indicated in Scheme 5. Thus... 

These y2 acetyl complexes 28,29 entail a metal-oxygen bonding (30) analogous to that established for bonding of organic ketones, esters, and amides to CpFe(C0)2+ (83). Sterically less... 

Further analysis of the spectral data for the P2"acetyl compounds 28 and 29 (Table 1) also indicates that the positive charge is distributed over both metal centers. The electronic environment of the C-bonded iron of 28 and 29 clearly lies intermediate between that of the starting acetyl complex and of the a-alkoxy-alkylidene compounds. Similarly the acetyl complexes provide more electron density to CpFe(CO)2+ within 28 than does acetone or THF within CpFe(C0)2Li+ [L =acetone, THF]. 

Insertion takes place between a Jt-bonded fragment and a a-bonded fragment in mutual cis-positions, as was described above. The de-insertion reaction can only proceed if there is a vacant site cis to the acyl group. The experiment outlined in Figure 2.12 proves this point. A manganese acetyl complex which is labelled with 13C at the acyl carbonyl group was synthesised and heated to give de-insertion of CO. The result was that the only product formed contained the methyl substituent in a position cis to the labelled 13C. 

This represents one pathway to the formation of methane, a knovm by-product in iridium catalysed methanol carbonylation. The hydrogenolysis reaction was severely retarded by the presence of excess CO, indicating a mechanism involving initial dissociation of CO from [MeIr(CO)2l3] , prior to activation of H2. The mechanism therefore resembles that for hydrogenolysis of Rh acetyl complexes in hydroformylation. 

Water is essential, since acetic acid is formed by the reaction between water and acetyl iodide or the Ni-acetyl complex. Acetic acid is also formed via the hydrolysis of any methyl acetate that is formed by methanol attack on acetyl iodide or the Ni-acetyl complex. 

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