Transition metal complexes amides

Terminal alkynes readily react with coordinatively unsaturated transition metal complexes to yield vinylidene complexes. If the vinylidene complex is sufficiently electrophilic, nucleophiles such as amides, alcohols or water can add to the a-carbon atom to yield heteroatom-substituted carbene complexes (Figure 2.10) [129 -135]. If the nucleophile is bound to the alkyne, intramolecular addition to the intermediate vinylidene will lead to the formation of heterocyclic carbene complexes [136-141]. Vinylidene complexes can further undergo [2 -i- 2] cycloadditions with imines, forming azetidin-2-ylidene complexes [142,143]. Cycloaddition to azines leads to the formation of pyrazolidin-3-ylidene complexes [143] (Table 2.7). 

From a historic point of view, metal-catalyzed or metal-promoted hydroamina-tions were first achieved with alkali metals [4]. The use of soluble transition-metal complexes as catalysts for the OHA reaction was pioneered by DuPont workers during the 1970s, the best results being obtained with Rh and Ir salts [5], Later, the finding that electron-rich Ir(I) species cleanly activated N—H bonds to form Ir-amido-hydrido species [6] opened the way to study the reactivity of these amides... 

The association number of Li amides, such as LrN(SiMe3)2, organolithium compounds bound at the a-position to S or Se atoms, such as LiCH2SePh, and various transition metal complexes was determined at 0°C in THF or at —35°C in Et20, by differential vapor-pressure osmometry. The method allows handling compounds sensitive to autooxidation, moisture and temperature . ... 

A transition metal complex such as bpyNi(COD), generalized as LjNi, reacts with NCA in a complex reaction sequence that generates a propagating species XLV whose active center is a 5-membered amido-amidate metallacyclic complex. Propagation involves a nucleophilic attack by the amido nitrogen of the amido-amidate at the C-5 carbonyl of NCA. The... 

The thermodynamics of the oxidative addition process tends to be favored by increased electron density at the metal centre, hence the focus on later transition metal derivatives. Furthermore, as discussed above, it is believed that M—N n-bonds to the later transition metals are of significance only if the transition metal complex is unsaturated. Saturated late transition metal amides (parent or substimted) often exhibit the so-called n-conflict (see above) so that the nitrogen centre displays no n-bonding to the metal and retains its lone pair character and basicity. 

The product amido-hydride is the first structurally characterized transition metal complex that features both a terminal amide and hydride. The X-ray crystal structure shows that the nitrogen centre has planar coordination. This geometry results from 71-bonding between the nitrogen electron pair and the lowest unoccupied metal orbital which lies in the equatorial coordination plane of the atoms lr(Ci ethine)(H)(N). This is consistent with earlier calculations on related species. The possibility that the addition of... 

Several reports have described the formation of alkyl formates or form-amides from C02, hydrogen, and an alcohol or amine. The earlier catalytic preparations have been reviewed (108). A recent paper describes the production of alkyl formates catalyzed by several transition metal complexes and tertiary amines under 25 atm each of C02 and H2 at 140°C, (78) (159). 

Another interesting and potentially very useful group of calixarene-based anion receptors is represented by systems with appended transition metal complexes of 2,2-bipyridine units. Technically, these systems utilise classical hydrogen bonding interactions of amidic/urea functions hence, from this point of view, they do not differ from many other receptors. On the other hand, the covalent attachment of bipyridine complexes of ruthenium(II) or rhe-... 

These two reactions are limited by the fact that a nitro group must be present on the benzene ring to facilitate the elimination of the chlorine atom. However, this restriction may be removed by the use of a transition-metal complex—most often, a nickel(O) catalyst. The starting compounds are 2-iodobenzoic acid derivatives 91 (amides, nitriles, and esters) and MA-disubstituted thioureas. In this case, electron-acceptor groups in the benzene ring are not obligatory the reaction is general and allows one... 

---