Metals metal-directed condensation

The macrocyclic tetraene 2,3,9,10-Me4[14]tetraene (tmt) may be synthesized by a metal-directed condensation between trimethylenediamine (tn) and 2,3-butanedione in the presence of Co(OAc)2, ultimately resulting in the trans-dichloro Co111 complex [Co(tmt)Cl2]+ (59).302... 

It has been well established that metal-directed condensation between metal-coordinated primary amines with aldehydes and dibasic acids such as nitroalkanes or primary amines provide a ready route to selected pendant arm maciocyclic ligands and their metal complexes [20], In such a reaction a new six-membered chelate ring is... 

The template synthesis of macrocyclic complexes rra 5-[M(L9)]" (M"" = Ni, Co +, Fe +) from 1-phenyl-1,2-propanedione and 1,3-diaminopropane occurs [44] according to Scheme 1-2. Reaction (1) represents the organic reaction prior to addition of a metal salt. When a methanolic solution of the latter is added to the reaction mixture, the metal-directed condensation is realised, producing the carbi-nolamine and final products. It is obvious that reaction (2) is a consequence of shifting the position of tautomeric equilibrium under the influence of a metal ion exclusively towards [M(L9)] , the latter subsequently being transformed into [M(L10)]"+. That the condensation reaction actually takes place within the metal coordination sphere has been demonstrated by the isolation of the corresponding cobalt(III) macrocyclic complexes with L9. 

The cis dione LI85 appeares to be a suitable ligson for metal-directed condensation with various diamines [238], as well as with diethylenetriamine [239], to give the macrocyclic compounds LI91-LI96 as corresponding complexes (Eq. 2.121). 

The ligands L1783 and L1784 were synthesised by a metal-directed condensation, around two copper(II) centres, of LI 781 and L1782 with nitroethane and formaldehyde (Eq. 8.52) [128, 129]. 

A Japanese patent has claimed improvements in the direct condensation of menadione with phytyl chloride in the presence of a reducing metal such as 2inc or iron powder (30). Tin chloride has been reported to be a useful catalyst for this condensation (31,32). 

Saline Water for Municipal Distribution. Only a very small amount of potable water is actually taken by people or animals internally, and it is quite uneconomical to desalinate all municipally piped water, although all distributed water must be clear and free of harmful bacteria. Most of the water piped to cities and industry is used for Htfle more than to carry off small amounts of waste materials or waste heat. In many locations, seawater can be used for most of this service. If chlorination is requited, it can be accompHshed by direct electrolysis of the dissolved salt (21). Arrayed against the obvious advantage of economy, there are several disadvantages use of seawater requites different detergents sewage treatment plants must be modified the usual metal pipes, pumps, condensers, coolers, meters, and other equipment corrode more readily chlorination could cause environmental poUution and dual water systems must be built and maintained. 

In the solid state, metal clusters can connect to each other through outer and/ or inner ligands, or by direct condensation of the metal octahedra (Fig. 6.2), to form a variety of frameworks. 

Our own group is also involved in the development of domino multicomponent reactions for the synthesis of heterocycles of both pharmacologic and synthetic interest [156]. In particular, we recently reported a totally regioselective and metal-free Michael addition-initiated three-component substrate directed route to polysubstituted pyridines from 1,3-dicarbonyls. Thus, the direct condensation of 1,3-diketones, (3-ketoesters, or p-ketoamides with a,p-unsaturated aldehydes or ketones with a synthetic equivalent of ammonia, under heterogeneous catalysis by 4 A molecular sieves, provided the desired heterocycles after in situ oxidation (Scheme 56) [157]. A mechanistic study demonstrated that the first step of the sequence was a molecular sieves-promoted Michael addition between the 1,3-dicarbonyl and the cx,p-unsaturated carbonyl compound. The corresponding 1,5-dicarbonyl adduct then reacts with the ammonia source leading to a DHP derivative, which is spontaneously converted to the aromatized product. 

Direct condensation of metal vapors with trifluorophosphine at -196°C provides a convenient alternative to the high-pressure route to metal-PF3 complexes. The reactions of Mo, Cr, Co, Ni, and Pd vapors with PF3 yield only one volatile product in each case, namely Mo(PF3)6 (132), Cr(PF3)6, Co2(PF3)g, Ni(PF3)4, and Pd(PF3)4 (128), respectively. The yields are good, 40-100% depending on the metal vapor used. Some defluorination of the PF3 accompanies the formation of Cr(PF3)6. No complex could be isolated from the manganese vapor-PF3 reaction, although some defluorination seems to have occurred. The reaction of iron and PF3 is complex,... 

The position of the equilibrium between imine and carbonyl may be perturbed by interaction with a metal ion. We saw in Chapter 2 how back-donation of electrons from suitable orbitals of a metal ion may stabilise an imine by occupancy of the jc level. It is possible to form very simple imines which cannot usually be obtained as the free ligands by conducting the condensation of amine and carbonyl compounds in the presence of a metal ion. Reactions which result in the formation of imines are considered in this chapter even in cases where there is no evidence for prior co-ordination of the amine nucleophile to a metal centre. Although low yields of the free ligand may be obtained from the metal-free reaction, the ease of isolation of the metal complex, combined with the higher yields, make the metal-directed procedure the method of choice in many cases. An example is presented in Fig. 5-47. In the absence of a metal ion, only low yields of the diimine are obtained from the reaction of diacetyl with methylamine. When the reaction is conducted in the presence of iron(n) salts, the iron(n) complex of the diimine (5.23) is obtained in good yield. 

As in the case of the metal-free direct dyes, a large diversity of structures is encountered here, too, there are direct dyes with pyrazolones, substituted 4,4 -diphenylamines, or the 1,3,5-triazine ring, urea and stilbene derivatives, and condensation dyes. 

Recent experiments by Citrin and coworkers (41) have clarified the role of the support in photoemission from small metal clusters. They condensed several monolayers of krypton onto either platinum or sodium metal substrates. By varying the thickness of the krypton from one to ten monolayers, the surface could be converted from metal to semimetal to insulator. The krypton peak position provides a direct measure of the sample vacuum level (32). The krypton layers are thin, less than 10 monolayers, so that the vacuum level is determined by the metal substrate. Onto the krypton layers, sodium clusters were deposited at varying coverages. Shifts in the Kr 4s and Na 2p binding energies were recorded relative to the Fermi level of the grounded substrate. 

In variations of the techniques, carrier gases such as He, H2, and N2 (which offer disadvantages owing to noncondensability) as well as condensable carrier gas, such as H2O, CO2, and heptane have been employed. Also, it is possible to deposit mirrors not only by evaporation of metals directly but by decomposition of metal-organic compounds. ... 

Direct condensation of 2,3,5-tri-0-benzoyI-/3-D-ribofuranosyl bromide with adenine in acetonitrile at 50 °C leads after deblocking to the 3-/3-D-ribofuranosyladenine (132) (B-68MI40901). Metal derivatives of purines tend to produce 7- or 9-glycosyl derivatives thus the silver salt of 2,8-dichloroadenine with 2,3,5-tri-O-acetylribofuranosyl chloride produces the 9-/3-D-ribofuranosyl derivative (133) (48JCS967, 48JCS1685). However similar reactions with theobromine produce O-glycosides and with theophylline N-7 derivatives (34JCS1639). 

Direct Combination of a 1,3-Diketone, an Amine, and a Metal Ion. Direct combination is a potentially useful reaction, and it has been used to prepare metal-salicylaldimine compounds. The procedure consists of mixing (and refluxing if necessary) a stoichiometric mixture of salicylaldehyde with an amine, a metal ion, and a base in dilute aqueous methanol. This procedure has not been applied commonly to the preparation of metal derivatives of jS-keto imines, although the preparation of 4,4 -(ethylene-dinitrilo)di-2-pentanonatocopper(II) from 2,4-pentanedi-one (acetylacetone), ethylenediamine, and copper has been described. Attempts to effect condensation of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (hexafluoroacetylacetone) and ethylenediamine by direct combination of the reactants in the presence of copper(II) acetate were imsuccessful. ... 

Figure 1 Compositional evolution of metal condensing at a pressure of 10 atm. The first metal to condense contains 19 3 wt.% Ni and decreases to the cosmic value of 5.7 wt.% Ni as cooling commences. Elements more refractory than Ni are enriched in the early condensates, whereas elements more volatile than Ni are depleted. Oxidation of Fe shifts the composition of the metal in the direction of the heavy arrows (Kelly and Larimer, 1977) (reproduced by permission of Elsevier from Geochim. Cosmochim. Acta, 1977, 41, 93-111).

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