Carboxylative dimerizations

Figure 17.8. Rhodium(II) carboxylate dimer, only one bridging carboxylate drawn...

Another method for reducing osmolality of the injection was achieved by the synthesis of mono-carboxylic dimers, leading to the development of ioxaglic acid (600 mOsm kg at 320 mgl mL ). Because of specific properties on platelet functions and thrombin generation, this agent is widely used for interventional procedures [3]. 

Rhodium(II) carboxylate dimers and their carboxamide counterparts have been demonstrated to be exceptionally useful catalysts for carbene transfer processes involving diazocarbonyl substrates [1]. Doyle s seminal work identified Rh2(OAc)4 as the catalyst of choice for a variety of cyclopropanation, C-H insertion, and ylide rearrangement transformations using diazoketones or diazoesters [2]. Important contributions by Taber [3], Padwa [4], and Davies [5] further established the superior catalytic activity of dirho-dium catalysts and the excellent selectivity of rhodium-[Pg.417]

V"-Boc-7Va -Z-L,L-diaminosuberic acid co-tert-butyl ester or bis(7V"-Boc)-L,L-diaminosuberic acid synthesized by the mixed Kolbe electrolytic carboxylative dimerization method was successfully utilized in the synthesis of nonreducible bicyclic analogues of somatostatin1491 or hematoregulatory peptide (pGlu-Glu-Asp)2-Dsu-(Lys)2, respectively.[50]... 

The carboxylic dimer has a center of symmetry only the asymmetrical C=0 stretching mode absorbs in the IR. Hydrogen bonding and resonance weaken the C=0 bond, resulting in absorption at a lower frequency than the monomer. The C=0 group in dimerized saturated aliphatic acids absorbs in the region of 1720-1706 cm1. 

The structure of the Mo2 (EtXant)4 2C4 Hg 0 contains a dimeric core similar to the one found in transition metal carboxylate dimers (550). The observed Mo—Mo distance of 2.125(1) A is very similar to that reported for the... 

It is reasonable to assume that the identical complex will be generated whether it be done stoichiometrically from an alkene, to give a chloride or carboxylate dimer followed by the addition of 2 equiv. of a phosphine per Pd, or by the addition of an allyl-X compound to give a phosphine-Pd0 complex. This assumption is supported by the fact that complexes generated in either manner have been found to exhibit identical reaction profiles.380 Furthermore, for the vast majority of allylpalladium reactions studied, it is most likely that the reactive species is a cationic bisphosphine-palladium complex (13).13 Calculations... 

Fig. 21 Stoichiometric reaction of C02 with rare-earth metal alkyl complexes to produce carboxylate dimeric catalysts...

The boronic acid (B), carboxylic acid (C), and primary amide (A) were first used in pairwise competitions with 1 equiv. of each guest (relative to the extended capsule). Separate signals are seen for the N-H resonances of the benzamide and phenyl boronic acid co-encapsulated with corresponding carboxylic acids (Fig. 11). All three combinations and their respective homodimers were observed. The symmetrical homodimers are half as probable as the heterodimers with distributions of 25% and 50%, respectively. The carboxylic acid (C) and amide (A) formed a heterodimer (BC = 53%) but its concentration is 4.8 times that of the underrepresented amide dimer (AA =11%) and 1.5 times that of the carboxyl dimer (CC = 36%). The BC heterodimer matches the best donor with the best acceptor but its concentration is merely what is statistically expected. The real difference is... 

Figure 11. Relevant AOs for rotation barrier and antiferromagnetism studies of N2O4 and Cu(II) carboxylate dimers.

The formation of a dimerized extracted species was first reported for the extraction of copper(II) with propanoic acid (40, 41). Later, nickel and cobalt were found to be extracted as dimers (22), and a mixed copper(II) carboxylate dimer involving acetate and decanoate was reported (147). More recently, attention has been drawn to the extraction of heteropolynuclear metal carboxylates (90, 91). 

Bold and Balu escu (13) found the monomeric copper(II) a-bromostearate CuA2(HA)2 in the extraction of Cu(II) with a-bromostearic acid in benzene. The bromine in the a-position was said to prevent sterically the formation of dimeric copper(II) species, a-Bromocarboxylic acid, being stronger than the nonsubstituted hom-ologues, is anticipated to form a less stable copper carboxylate dimer. 

Tautomerization of naphthazarin and tropolone in crystals 230 Tautomerization of carboxylic dimers in crystals 233 Double-proton transfer in porphyrins 236 Multiple proton transfer in pyrazoles 240... 

Fig. 9 Potential curve of the double-proton transfer between two configurations of carboxylic dimers. A denotes the energy difference between two configurations.

The carboxylate dimers resemble, in some ways, the dimeric alkoxides with multiple metal-metal bonds. This chemistry has been extensively developed by Chisholm and coworkers. These complexes react with CO to cleave the metal metal bond, as shown in equation (36). 

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