Olefin structures carbonylation

Pauson s work on the structure and bonding of butadiene iron tricarbonyl launched a series of studies making the chemistry of olefin metal carbonyls an... 

Further evidence for heterolytic decomposition is obtained from the effect of olefin structure on product distribution. Table II shows the ratio of carbonyl to glycol product for three olefins. Listed for comparison is the carbonyl/glycol ratio for the chlorohydrin, which corresponds to the structure of the oxythallation adduct from ethylene and propylene. The effect of structure on the ratio is qualitatively the same for the thallic ion oxidation and the hydrolysis of the corresponding chlorohydrin. Since the product distributions for both are inconsistent with neighboring hydroxyl participation (Reaction 33) the carbonyl/glycol ratio is a measure of the competition between hydride shift vs. water attack in... 

The n-C H was obtained from Fluka AG, Switzerland as puriss quality. No irregular structures such as tertiary carbon-atoms, olefinic or carbonyl groups could be detected by IR and NMR. 

Subsequently, a number of authors have considered non-planar distortions of olefins and carbonyl groups as a source of diastereofacial selectivity, often emphasizing non-equivalent FMO extension (polarization of the frontier orbitals with respect to the a plane) or asymmetry of the electrostatic potential, rather than the actual geometry distortion [198, 199]. Interest in the latter, however, was revived by the end of the 70 s, stimulated by the early papers on structure correlation as well as several other contributions at that time. One of them was the seminal study by Eschenmoser and Dunitz and their coworkers in 1976, who examined conformations and nonplanarity of enamine fragments in a number of crystal structures in search for the origin of face selection in condensations of chiral enamines [200]. Another crucial development appears to be Bartlett and Watson s discovery that large pyramidaliza-... 

As mentioned above, hydroformylation reactions occur under atmospheric pressure at normal temperature with stoichiometric amounts of cobalt carbonyls. However, with catalytic amounts of cobalt catalysts a minimum CO partial pressure is necessary for reformation and stability of Co2(CO)8, or HCo(CO)4, as the case may be (see page 15). A small increase of the CO partial pressure above this value first results in an increase of the reaction velocity until a maximum is reached depending on temperature and olefin structure. However, further increase of the CO-partial pressure causes a decrease in the reaction velocity [38, 40, 120], (see also section on reaction mechanism). 

Ozonolysis has been very often used to convert double bonds into carbonyl-containing compounds on solid phase but there are only a few examples for the release of olefinic structures from polymer support using this methodology. While transformations including the use of rutheniiun catalysts (see metathesis cleavage) tolerate many functionalities including carboxylic acids and their anhydrides, amides, aldehydes, ketones, alcohols and sulfonamides [370], ozonolysis stands for harsh conditions and compatibihty with only a few fimctional groups. Nevertheless, there are examples for the release of diverse compounds from solid phase as demonstrated by Hall and Sutherland [383], Frechet and Schuerch [384] and Martinez et al. [385,386]. 

The initial step of olefin formation is a nucleophilic addition of the negatively polarized ylide carbon center (see the resonance structure 1 above) to the carbonyl carbon center of an aldehyde or ketone. A betain 8 is thus formed, which can cyclize to give the oxaphosphetane 9 as an intermediate. The latter decomposes to yield a trisubstituted phosphine oxide 4—e.g. triphenylphosphine oxide (with R = Ph) and an alkene 3. The driving force for that reaction is the formation of the strong double bond between phosphorus and oxygen ... 

This reviews contends that, throughout the known examples of facial selections, from classical to recently discovered ones, a key role is played by the unsymmetri-zation of the orbital phase environments of n reaction centers arising from first-order perturbation, that is, the unsymmetrization of the orbital phase environment of the relevant n orbitals. This asymmetry of the n orbitals, if it occurs along the trajectory of addition, is proposed to be generally involved in facial selection in sterically unbiased systems. Experimentally, carbonyl and related olefin compounds, which bear a similar structural motif, exhibit the same facial preference in most cases, particularly in the cases of adamantanes. This feature seems to be compatible with the Cieplak model. However, this is not always the case for other types of molecules, or in reactions such as Diels-Alder cycloaddition. In contrast, unsymmetrization of orbital phase environment, including SOI in Diels-Alder reactions, is a general concept as a contributor to facial selectivity. Other interpretations of facial selectivities have also been reviewed [174-180]. 

NMR spectroscopic studies f111,13C, and 31P) are consistent with the dipolar ylide structure and suggest only a minor contribution from the ylene structure.234 Theoretical calculations support this view.235 The phosphonium ylides react with carbonyl compounds to give olefins and the phosphine oxide. 

Olefination Reactions Involving Phosphonium Ylides. The synthetic potential of phosphonium ylides was developed initially by G. Wittig and his associates at the University of Heidelberg. The reaction of a phosphonium ylide with an aldehyde or ketone introduces a carbon-carbon double bond in place of the carbonyl bond. The mechanism originally proposed involves an addition of the nucleophilic ylide carbon to the carbonyl group to form a dipolar intermediate (a betaine), followed by elimination of a phosphine oxide. The elimination is presumed to occur after formation of a four-membered oxaphosphetane intermediate. An alternative mechanism proposes direct formation of the oxaphosphetane by a cycloaddition reaction.236 There have been several computational studies that find the oxaphosphetane structure to be an intermediate.237 Oxaphosphetane intermediates have been observed by NMR studies at low temperature.238 Betaine intermediates have been observed only under special conditions that retard the cyclization and elimination steps.239... 

Ni catalysts for olefin polymerization incorporating a-iminocarboxamide ligands are activated by the formation of borane-carbonyl adducts (153).542 Structure/reactivity relationships are similar to Brookhart s dimine catalysts. 

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