Carbon dioxide ligand effects

Further examples of rotational isomerism in phosphine complexes include the conrotatory motion of carbon dioxide ligands in rra 5-[Mo(C02)2 (PMe3)2(P-P)] and frons-[Mo(C02)2(P-P)2] where P-P is a chelating diphosphine,and Rh—P bond rotations in cis-[Rh(COD)(phosphine)2] complexes.In the latter study rotation barriers were sensitive to the substituent orientation at the P donor atom. Differences in catalytic activity/ selectivity of these complexes were found to parallel the influence of interligand steric effects on Rh—P bond rotation dynamics. 

We have utilized somewhat less-effective optional approaches to copolymer purification with attendant catalyst recovery. One of these methods involved the replacement of the f-butyl substituents on the 5-position of the phenolate ligands with poly(isobutylene) (PIB) groups, as illustrated in Fig. 14 [39]. Importantly, this chromium(III) catalyst exhibited nearly identical activity as its 3,5-di-t-butyl analog for the copolymerization of cyclohexene oxide and carbon dioxide. The PIB substituents on the (salen)CrCl catalysts provide high solubility in heptanes once the copolymer is separated from the metal center by a weak acid. 

The reaction of C02 with Ir(CH3)CO(02)[P(p-tolyl)3]2 also results in the formation of a peroxycarbonate complex (191) via external attack by carbon dioxide. In this case, however, only gaseous carbon dioxide is required, rather than the more strenuous conditions of liquid C02. This same complex reacts with gaseous carbon monoxide to form the carbonate complex. Labeling experiments demonstrate that the coordinated CO does not participate in the reaction External attack by the added CO is responsible for the reaction (191). Coordinated CO has been shown to react with bound dioxygen, as is seen in Scheme 16. In this case, the chelating triphos ligand obviously has a significant effect on the reactivity (189). 

Carbomethoxy-2-cyclohexen-l-one, 289 Carbon dioxide point group of, 5 Carbon monoxide (CO) complex with BF3, 304 effect on Ao, 181 as L ligand, 176 point group of, 5 trans effect, 181... 

The procedure described here is based on the observation that amine monohydroxo complexes of cobalt(III), rhodium(IIl), and iridium(III) react directly with carbon dioxide to form the corresponding carbonato complexes,2 3 without effect on the configuration of the amine ligands.4 The amine monoaqua complex is allowed to react with lithium carbonate or carbon dioxide gas at room temperature at pH 8.0 for a few minutes, and the carbonato complex is isolated by adding alcohol. The procedure has been used to prepare salts of the following cations pentaammine(carbonato)-cobalt(III),2 ds-ammine(carbonato)bis(ethylenediamine)cobalt(III),5 trans-... 

Urethanes. Methyl carbamates (1) can be prepared from primary or secondary amines, alkyl halides, and carbon dioxide in a reaction promoted by copper(I) /-butoxide (equation I). The ligand t-butyl isocyanide can be replaced with tri-n-butylphosphine. Copper(I) f-butoxide is more effective than other copper salts. In the case of diethylamine, the intermediates a and b were isolated and b was converted to the methyl carbamate in 86% yield. 

A range of metal catalysts have also been studied in aqueous solution for the transformation of carbon dioxide, including rhodium, ruthenium and iridium bipyridine or phenanthroline complexes.One of the most effective systems is the iridium complex shown in Figure 3.14. The ligand design concept used in this study is very clever. The catalytic activity of the complex and its solubility in aqueous solution can be tuned by the pH of the solution.Under acidic... 

An intramolecular version of this process has been described, leading to bicyclic 2-pyrones. Diynes in which both alkyne functions are internal and are linked by three-, four- or five-atom chains cycloadd to carbon dioxide in the presence of catalytic Ni° and various trialkylphosphines (equation 51). Terminal diynes require stoichiometric metal and give lower yields, however. Extensive studies of ligand effects on yield and chemoselectivity have established a broad scope for the process and pointed out important practical differences between it and the intermolecular reactions described above. ... 

A Cu(II) complex with a bipyridine-type ligand (Cu-4) is effective in the controlled polymerization of styrene and acrylates in the presence of Al(0-i-Pr)3, which most probably serves as a reducing agent of Cu(II) into Cu(I).93-94 A fluoroalkyl-substituted bipyridine ligand (L-7) was also employed in supercritical carbon dioxide for the polymerization of fluorinated acrylates and methacrylates.95 Similar pyridine-based bidentate ligands, 1,10-phenanthroline and its... 

Noyori was subsequently able to show that triethylamine salts of formic acid (TEAF) could be used to reduce ketones to alcohols and imines to amines with high enantioselectivities [4]. The byproduct of this reaction is carbon dioxide gas and this prevents the possibility of the reverse reaction. Strangely, aminoalcohol ligands are poor in this reaction, whilst unsymmetrical 1,2-diamines have proven very effective. A particularly effective ligand is mono-N-tosyl-l,2-diphenylethylene-diamine. 

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