Clusters reaction with anilines

The presence of lithium chloride alters the chemistry, presumably by coordination to intermediary species during cluster self-assembly. Thus, the addition of one equivalent of LiCl to 9 yields the chloride adduct 12 further treatment with one equivalent of r-butylamine leads to neutral cubane 5, but at a much reduced rate compared to the reaction without LiCl. The reaction with aniline is also retarded in the presence of LiCl, and the formation of azobenzene is significantly diminished. We have identified three products from this reaction... 

Meio-epoxides undergo a ring-opening reaction with aromatic amines in the presence of a chiral metal-organic framework catalyst Zn2(L)(H20)2(A,A -dimethylacetamide)4 where L, [(S)-6,6 -dichloro-2,2 -diethoxy-1,T-binaphthyl-4,4 -bis(5-isophthalic acid)] is an organic linker between the zinc clusters Yields of the a-hydroxyamine ranging i from 70 to 95% with 62-89% ee were obtained using CM-stilbene epoxide and aniline. Lower yields and much lower ee values were found when different substituents were on the stilbene epoxide or the aniline. 

It has been found in the meantime that reaction (1) is generalizable (752), and that oxidative additions of this type occur for such widely differing substrates H2Y as ethylene, benzene 130), cyclic olefins, alkyl and aryl phosphines, aniline 337, 406), and H2S 130), ail of which give the same product structure with a triply-bridging Y ligand. The stability of these third-row transition metal clusters has stiU prevented catalytic reactions of these species, but it is likely that similar ones are involved in olefin and acetylene reactions catalyzed by other metal complexes. 

It has been known that the reaction of copper(I) iodide with Lewis bases, such as aniline derivatives, produced complexes with single cubane-like CU4I4 cluster, in which the aniline derivatives act as the terminal ligands coordinating to the copper(I) centers [7-10]. Thus, it is reasonable to expect macrocyclic or extended complexes constructed by CU4I4 cluster units through replacing aniline derivatives with ditopic... 

The nse of polysnlfide complexes in catalysis has been discnssed. Two major classes of reactions are apparent (1) hydrogen activation and (2) electron transfers. For example, [CpMo(S)(SH)]2 catalyzes the conversion of nitrobenzene to aniline at room temperature, while (CpMo(S))2S2CH2 catalyzes a number of reactions snch as the conversion of bromoethylbenzene to ethylbenzene and the rednction of acetyl chloride, as well as the rednction of alkynes to the corresponding cw-alkenes. Electron transfer reactions see Electron Transfer in Coordination Compounds) have been studied because of their relevance to biological processes (in, for example, ferrodoxins), and these cluster compounds are dealt with in Iron-Sulfur Proteins. Other studies include the use of metal polysulfide complexes as catalysts for the photolytic reduction of water by THF and copper compounds for the hydration of acetylene to acetaldehyde. ... 

Hydridic cluster anions are also important in the homogeneous WGSR cata-lysis.t The mechanism of WGSR reactions occurring on Ru3(CO)i2 with an acid cocatalyst (CF3COOH) has been fully elucidated.The radical anion [Fe3(CO)ii], obtained in the phase-transfer-catalyzed reaction of Fe3(CO)i2 with OH , catalyzes the reduction of nitrobenzene to aniline. 

The cluster Ru3(CO)i2 is known to react in the presence of bases to afford, under certain experimental conditions, [HRu3(CO)u] [42]. Since the corresponding iron cluster is known to react with nitrobenzene to yield an hydrido imido cluster [HFe3(CO)9(NPh)] , which can be protonated and afford small amounts of aniline [43], a catalytic cycle was proposed, and supported by some model reactions, for the ruthenium-catalysed reduction of nitroarenes by CO/H2O, which includes the intermediate formation of the trinuclear hydrido cluster [44-46]. However, one of us has recently shown that [HFe3(CO)n] and the corresponding imido complex play no role in the Fe3(CO)i2-promoted reduction of nitrobenzene [6, 47] and the proposal of an active role of [HRu3(CO)ii] appears to be questionable. 

A discussion was reported in the paper [72] on the identity of the catalytically active species even with other rhodium-based catalytic systems. Based on the data reported in the literature and collected in our laboratories on the reactions of rhodium clusters with CO and bases, it was proposed that the only function of the base in all other rhodium-based catalytic systems for the reduction of nitrobenzene to aniline is simply to generate [Rh(CO)4], with chelating bases being much more effective than non-chelating ones. Once this last complex has been generated, the base in useless and may even have a negative effect on the reaction. This explains why, when [Rh(CO)4] is used as catalyst, higher activities are obtained and no base is required. 

Bimetallic phase-transfer-catalysis is a process whereby a reaction that occurs using two different metal complexes, does not proceed in the absence of either metal species, or proceeds only at reduced rate. An apparent system of this class has been reported, in which Co2(CO)g and [RhCl(l,5-hexadiene)]2 mutually increased their reactivity when used as catalysts for the conversion of nitrobenzene to aniline in a biphasic system (benzene, aqueous NaOH, dodecyltrimethylammonium chloride) in a carbon monoxide atmosphere [73]. However, another member of the same research group later showed [74] that the apparent bimetallic promotion was due to the fact that the alkylammonium salt used as a phase-transfer agent actually inhibited the activity of the active rhodium complex (apparently a cluster, which is active in the absence of both the alkylammonium salt and the cobalt compound) by rendering it insoluble. The added Co2(CO)g reacts with the alkylammonium salt to generate... 

Catalytic systems based on rhodium clusters or [Rh(CO)4] for the carbonylation of nitro compounds to carbamates have been described in Chapter 3. The application of the same or similar systems to the reduction of nitro compounds to anilines have been described in Chapter 4. Initial work has shown that rhodium clusters Rh4(CO)i2 and Rh<5(CO)i6, but even several mononuclear compounds such as Rh(CO)2(acac) (acac = acetylacetonate), are active catalyst precursor for the carbonylation of nitrobenzene to carbamates, when promoted by an heterocyclic nitrogen base [56, 140, 187, 188]. Later, Liu and Cheng and us independently reported that even higher catalytic activities could be obtained by the use of preformed [PPN][Rh(CO)4] (PPN = (PPh3)2N ) [189, 190]. We have also conducted a mechanistic study of the catalytic cycle using this last complex [1, 192] and the initial stage of the reaction has also been reinvestigated by Liu et al. [193]. Since no mechanistic study has been yet reported on the cluster-based systems, we will first discuss the [PPN][Rh(CO)4] system and then draw a comparison with the other systems. 

In addition to the electron-precise 48e hydrido cluster anion 2, the 47e-radical anion, [Fe3(CO)nl 3, is regarded as a key intermediate in reductive transformation of nitroaromatics to anilines or their carbonylated derivatives. The radical 3 is formed via a redox disproportionation reaction upon treatment of 1 with halide (Cl, Br, I ) or pseudohalide (NCO ) in THF in contrast to the reactions of the Ru and Os derivatives, which afford the diamagnetic substituted anions, [M3(CO)io(/t-X)] Treatment of iron carbonyls such as 1 with trimethylamine iV-oxidc or... 

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