Azines metal complexes

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). 

Azo dyes make up the major proportion of the direct dyes apart from these, only a few azine, phthalocyanine, and nonazo metal-complex dyes possess a certain significance. The following structural characteristics are necessary for high substantivity ... 

A plethora of electron-deficient arenes can enter the VNS reaction carbocyclic and heterocyclic aromatic compounds activated by the nitro group and arenes that are active electrophiles due to their electronic configuration, such as azulene [35, 36], electron-deficient annulenes [37], tropylium cation [38], and particularly azines and azinium cations. Interestingly, q -transition metal complexes of arenes, such as benzene tricarbonylchromium, do not enter the VNS reactions. Although the addition of carbanions to these electron-deficient rings proceeds efficiently, and these adducts can be oxidized to form the products of ONSH, the p-elimination of HCl from the o adducts of a-halocarbanions does not occur [39, 40]. 

J. Ridley and M. Zerner, Theoret. Chim. Acta, 32, 111 (1973). An Intermediate Neglect of Differential Overlap Technique for Spectroscopy Pyrrole and the Azines A. D. Bacon and M. C. Zerner, Theoret. Chim. Acta, S3,21 (1979). An Intermediate Neglect of Differential Overlap Theory for Transition Metal Complexes Fe, Co, and Cu Chlorides W. D. Edwards and M. C. Zerner, Theoret. Chim. Acta, 72, 347 (1987). A Generalized Restricted Open-Shell Fock Operator. 

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. 

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],... 

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]. 

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