Amide-palladium interaction

This same two-step diamination process was employed in the palladiuminternal alkenes (Scheme 4.11) [35]. Here, 2,2 -diamino stilbene derivatives were converted into the corresponding diamines with complete diaster-eoselectivity (Eq. (4.25)). This stereochemical outcome was rationalized by the assumption of an initial amide-palladium interaction, which is unproductive regarding a possible syn-aminopalladation as it would generate an azetidine intermediate. Instead, trans-aminopalladation takes place, followed by rapid oxidation to an q -coordinated benzylic palladium(IV) with preservation of the relative stereochemistry. Anti-C-N-bond formation then displaces palladium(II) to close the catalytic cycle and to displace the C2-symmetric diamine product. 

In conjugate reduction of enones with other transition metals such as chromium, the rates of reduction were shown to be dependent on the conformation of the substrate, with faster reactions being observed with the cisoid forms as compared with the transoid onesJ However, with the Pd/Si/Zn system, the rigid transoid enone of cyclohexenone and the flexible enone of acetylcyclohexene are both reduced in comparable rates. This indicates that palladium interacts exclusively with the olefinic part of the enone without significant participation of the carbonyl. Interestingly, this method is highly selective for unsaturated ketones and aldehydes, as the reduction of corresponding o,jS-unsaturated carboxylic acid derivatives, such as esters, amides, and nitriles, is very slow under the conditions used. Thus, ben-zylideneacetone is selectively and cleanly reduced in the presence of methyl cinnamate, dnnamonitrile, or dnnamamide.t" ... 

Reductions of nitronitriles situated to favor interaction are apt to involve both functions (S4,93). Hydrogenation of o-nitrobenzonitrile over either palladium or platinum gave o-aminobenzamide (78), with the amide oxygen transferred from the nitro group (66). On the other hand, l-amino-2-cyanonaphthalene gave the amino amide on reduction over Pt02, but the amino nitrile over palladium (82). 

Kaneda et al. [33,34] have recently utilized acid-base interactions to non-covalently attach diphenylphosphine-4-benzoic acid palladium complexes to the exterior of poly(propyleneimine) dendrimers and to cavities within these dendrimers (Fig. 9) via the interaction of the benzoic acid with the carboxyl groups of amide moieties positioned within the dendrimer. Interestingly, the supramolecular dendritic catalyst gave rise to much more active catalysts for... 

The catalytic activity and selectivity of platinum, palladium, rhodium and ruthenium salts supported on various polyamides was studied, and the correlation between their reduction capability to the metallic state and the formation of coordination complexes with polyamide was established [115]. Concerning supported metals, the influence of the geometrical factor and the feasibility of electronic interaction of the supported metal with polyamide was discussed. It was found that the activity of Rh complexes decreases with an increase in the distance between amide groups of polyamide and correlates with the change in polymer crystallinity [107]. 

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