Transition-metal-promoted carboxylation

Main Croup Element- and Transition Metal-Promoted Carboxylation of Organic Substrates (Alkanes, Alkenes, Alkynes, Aromatics, and Others)... 

Main Croup Element- and Transition Metal-Promoted Carboxylation 5.2... 

Transition metals promote formation of w-allyl complexes from dienes by nucleophilic attack. Different nucleophiles and dienes participate in the reaction, which may take two routes where the nucleophile and the metal add either from the same (path a) or the opposite face of the diene (path b). Nucleophiles may be divided into two classes one, which includes alcohols, amines, carboxylates and malonates, reacts preferentially according to (a) ... 

Transition-metal catalyzed decomposition of alkyl diazoacetates in the presence of acetylenes offers direct access to cyclopropene carboxylates 224 in some cases, the bicyclobutane derivatives 225 were isolated as minor by-products. It seems justified to state that the traditional copper catalysts have been superseded meanwhile by Rh2(OAc)4, because of higher yields and milder reaction conditions217,218) (Table 17). [(n3-C3H5)PdCl]2 has been shown to promote cyclopropenation of 2-butyne with ethyl diazoacetate under very mild conditions, too 2l9), but obviously, this variant did not achieve general usage. Moreover, Rh2(OAc)4 proved to be the much more efficient catalyst in this special case (see Table 17). 

While the above indicates that Ln3 + and transition metal ions in the presence of at least 1 equi. of OR promote the alcoholysis of carboxylate and phosphate esters, sometimes by spectacular amounts, we have not presented evidence about the mechanism for the catalytic reactions. So far, the underlying theme is that the most active forms of the lanthanide ions are the Ln3 + ( OR) forms, either as a monomer (as in the case of Eu3 + ( OCH3)) or as a dimer (as in the case of La2+( OCH3)2). For the transition metal ions the most active forms are those where one face of the... 

As in the SETFICS and TALSPEAK processes, the DIAMEX-SANEX/HDEHP process involves selectively back-extracting the trivalent actinides by a hydrophilic polyamino-carboxylate complexing agent, HEDTA, in a citric acid buffered solution (pH 3). However, the combination of HDEHP and DMDOHEMA at high acidity promotes the coextraction of some block transition metals, such as Pd(II), Fe(III), Zr(IV), and Mo(VI), which must be dealt with by specific stripping steps (as described on Figure 3.26) that increase the total volume of the output streams ... 

Diazocarboxylate esters can be transformed by transition metal catalysts such as rhodium(II) acetate into alkoxycarbonylcarbenes that undergo a wide variety of synthetically useful C-H, C-C, C-X, X-H and X-X insertion reactions (where X = heteroatom) [99]. Chemoselectivity of rhodium carbenoids derived from Rh(II) carboxylates and carboxamides has been found to exhibit striking ligand dependency, for example in work by Padwa showing that perfluorocar-boxamide ligands exclusively promoted aromatic C-H insertions in Rh(II)-cat-alyzed decomposition of diazoamides to give oxindoles, whereas a carboxylate-based rhodium catalyst promoted other types of insertions and addition reactions [100]. 

In lakes, the pool of dissolved organic carbon (DOC) is dominated by dissolved humic substances (up to 80% of the DOC). Lake humic substances are similar to soil humic substances in that carboxyl, hydroxyl, phenol, and probably methoxyl groups are of major significance. Fluorescence spectra of DOC may be interpreted in terms of the different geochemical origins of DOC (e.g., allochthonous versus algal derived). One or more moieties of dissolved humic substances are produced autochthonously mechanisms may include polymerization of phenols (promoted by transition metals), Maillard condensations, or oxidation via phenolase systems. Aliphatic structural units in dissolved humic substances provide a flexible conformation to the humic substance molecule. ... 

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