Azines with metals

The factors in carboaromatic nucleophilic displacements summarized in this section are likely to be characteristic of heteroaromatic reactions and can be used to rationalize the behavior of azine derivatives. The effect of hydrogen bonding and of complexing with metal compounds in providing various degrees of electrophilic catalysis (cf. Section II, C) would be expected to be more extensive in heteroaromatics. 

Many publications are devoted to the synthesis of nitrile complexes, carried out by the immediate (direct) interaction of RCN and MX , mostly in the absence of a solvent [10, p. 95]. A series of N-donors, N-containing heterocyclic donors, whose complexes frequently model biologically important objects (Sec. 2.2.42), should be mentioned apart. The following compounds belong to this type azoles 188, azines 189, and their amino derivatives 572. Their interaction with metal salts takes place usually without a solvent with the use of liquid heterocyclic ligands, for example pyridine [10, ch. 4, p. 107 11], in alcohol or alcohol-aqueous mediums in cases of crystalline ligands (3.10)—(3.12). The specific conditions are presented in the literature, cited in Sec. 2.2.4.2. 

An important place among chelating ligands belongs to N,0-donors (Sec. 2.2.5.3) which, similarly to discussed above with N,N-donor ligand systems, allow us to create programmed metal-cycles of different size (Sec. 2.2.5.3 414, 418, 422, 424, 427, 428, 432, 433, 436, 438, 445, 446-449). To obtain metal chelates with four-member chelate unit, the interaction of, for example, 2-hydroxy derivatives of azines and metal salts is used (3.45) [52] ... 

The bottom line on monocyclic aromatic compounds with re-electron sextet is that so far, among six-membered systems only benzene, the azines with 1 through 4 nitrogen atoms, phosphabenzene and arsaben-zene, pyrylium, azapyrylium, chalcogenopyrylium cations (with or without exocyclic groups such as hydroxy, amino and corresponding tautomeric or prototropic forms), and the metallabenzenes with platinum family metals have been proved to afford stable molecules under normal conditions. The list is richer for five-membered systems. 

Complexing with metal ions or acylation with organic or inorganic reagents produces reversible oationization of azines. The formation of metal ion complexes may facilitate reactions, as in the amination of... 

Alternatively, the radical anions of pyridine and other azines are obtained on reduction by metals or other reducing agents, e.g. lithium diethylamide. Under suitable conditions the salts of the radical anions can be obtained as crystalline materials (Section 6.2.3). Alternatively, dimerization follows as an example, treatment of pyridine and other azines with 1 equiv. sodium in HMPA gives the well characterized radical anion, whereas in tetrahydrofuran the dimeric dianion is formed [125]. A later study with pyridine showed that treatment with sodium leads to a tetrahydro-4,4-bipyridine dianion (57), which is rearomatized to yield 58 in the presence of excess sodium (Scheme 40) [126], Treatment with LiNEt2 gives 2,2 -bipyridine, however, possibly because of stronger coordination with the lithium cation [127]. 2,2 -Biquinoline and 1,1 -biisoquinoline are similarly obtained [128]. 

The minimum inhibition concentrations (MIC) for a broad spectrum of fungi associated with metal working fluid deterioration or of economic importance in industrial problems were determined by Grier et al (1980) in comparison to the corresponding MIC of hexahydro-l,3,5-tris(2-hydroxyethyl)-5 -triazine (Table 31). Apparently there is no significant difference between the two hexahydro-5 -tri-azine derivatives in their activity against fungi. 

Apart from the above applications, hydrazine hydrate is also used in preparing organic derivatives, like hydrazones and hydrazides such as carbohydrazide (CH), oxalyl dihydrazide (ODH), malonic acid dihydra-zide (MDH), tetra formal tris azine (TFTA) and so on, from the corresponding ketones and aldehydes. Hydrazones have been investigated as solid fuels in hybrid rockets [40]. The hydrazides have been exploited as combustible fuels with metal nitrate oxidizers in the preparation of nanocrystalline oxide materials [41]. 

Sodium dichromate and various chromic salts are employed in the textile industry (195,196). The former is used as an oxidant and as a source of chromium, for example, to dye wool and synthetics with mordant acid dyes, oxidi2e vat dyes and indigosol dyes on wool, aftertreat direct dyes and sulfur dyes on cotton to improve washfastness, and oxidi2e dyed wool. Premera11i2ed dyes are also employed. These are hydroxya2o or a2omethine dyes in which chromium or other metals are combined in the dye (see Azine dyes DYES Azo dyes). 

As for cyclopropanation of alkenes with aryldiazomethanes, there seems to be only one report of a successful reaction with a group 9 transition metal catalyst Rh2(OAc)4 promotes phenylcyclopropane formation with phenyldiazomethane, but satisfactory yields are obtained only with vinyl ethers 4S) (Scheme 2). Cis- and trans-stilbene as well as benzalazine represent by-products of these reactions, and Rh2(OAc)4 has to be used in an unusually high concentration because the azine inhibits its catalytic activity. With most monosubstituted alkenes of Scheme 2, a preference for the Z-cyclopropane is observed similarly, -selectivity in cyclopropanation of cyclopentene is found. These selectivities are the exact opposite to those obtained in reactions of ethyl diazoacetate with the same olefins 45). Furthermore, they are temperature-dependent for example, the cisjtrcms ratio for l-ethoxy-2-phenylcyclopropane increases with decreasing temperature. 

In the analogous reaction of differently substituted azines RR C=NN=CRR , the products depend strongly on the metal used (Ti and Zr) as well as on the substituents R and R [43], With R = R = Me and M = Ti, substitution of the alkyne by the azine and subsequent CH activation of the complex 78 is observed. With R = Ph and R = H, the acetylene is also substituted and, through a reductive coupling of two azine molecules, the binudear Ti(III) complex 79 is formed. Using the zirconocene 2a, and with azine substituents R = Ph and R = H, no substitution of the alkyne is observed, but one of the C=N double bonds of the azine inserts into the Zr—C bond of the starting complex to yield complex 80. 

With R = R = Ph and using complexes 1 or 2a, the central N -N single bond of the azine is cleaved by both metals. In this case, the bis(imido) complexes 81 were formed, treatment of which with complexes such as CpCo(C2H2)2 can give heterobimetallic bis(alkylideneamido)-bridged complexes such as 82. Mach has used this concept for the reaction of methyl-substituted titanocenes with acetoneazine. With 3, monomeric Ti(III) complexes 83 and, after activation of the methyl groups, coupled products such as 84 could be obtained [44],... 

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). 

The normal byproducts formed during the transition metal-catalyzed decomposition of diazoalkanes are carbene dimers and azines [496,1023,1329], These products result from the reaction of carbene complexes with the carbene precursor. Their formation can be suppressed by slow addition (e.g. with a syringe motor) of a dilute solution of the diazo compound to the mixture of substrate and catalyst. Carbene dimerization can, however, also be a synthetically useful process. If, e.g., diazoacetone is treated with 0.1% RuClCpIPPhjij at 65 °C in toluene, cw-3-hexene-2,5-dione is obtained in 81% yield with high stereoselectivity [1038]. 

As with their monocyclic analogs, lithiated derivatives of bicyclic di-azines can be prepared by halogen-metal exchange at low temperature, and examples include the 6-lithiopurine 130 (79JOC4612), and the 5-and 7-lithio-3//-l,2,3-triazolo[4,5-(f pyrimidines 131 and 132 (91CPB2793, 91CPB3037). 

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