Metallic complex, of thiazoles

Mercuration, of alkylthiazoles, 380 as extractive technique, 380 Metallic complex, of thiazoles, 392 w Method, 27 ur" Method, 27... 

Experimental confirmation of the metal-nitrogen coordination of thiazole complexes was recently given by Pannell et al. (472), who studied the Cr(0), Mo(0), and W(0) pentacarbonyl complexes of thiazole (Th)M(CO)5. The infrared spectra are quite similar to those of the pyridine analogs the H-NMR resonance associated with 2- and 4-protons are sharper and possess fine structure, in contrast to the broad, featureless resonances of free thiazole ligands. This is expected since removal of electron density from nitrogen upon coordination reduces the N quad-rupole coupling constant that is responsible for the line broadening of the a protons. 

Aza-aromatic compounds can give rise to metallic complexes, and various complexes of thiazole have been studied ... 

All the early literature concerning thiazoles mentions numerous metallic complex-salts formed by addition to the thiazole of the aqueous solution of the metal salt and that could be used for identification purposes. The most usual complexes so obtained are platinum double salts, for example, (4-methylthiazole HC1)2 PtCU (m.p. deep 204°C) (25), or mercuric chloride derivatives, for example, 2,4-dimethyl-thiazole 2 HgCl (m.p. deep 176-177°C) (458). 

Benzo-l,3-thiazole-2-azide reacts with metal salts to give a mixture of complexes of both possible tautomeric forms 397 and 398 (Scheme 147) (75UKZ1238). However, this conclusion was made only on analysis of the IR spectra of the reaction products and should not be considered final. 

Most of the substrates that give both types of cycloaurated complexes are limited to pyridine derivatives, although recently a few exceptions have been reported with thiazoles and imidazoles. The reaction of substituted pyridine ligands such as phpy,1 49,1924 2-benzoyl pyridine,1924 2-anili-nopyridine,1925,1926 l-(2-pyridylamino and 2-pyrimidinylamino)naphthalene, 7 2-phenoxypyri-dine,1811 2-(phenylsulfanyl)pyridine,1925 2-(2-thienyl)pyridine, 8 2-(3-thienyl)pyridine,1928 2-(alkylsulfanyl)pyridine,1929 or papavorine1930 at room temperature yields the nonmetallated compounds which, upon heating, are transformed into the metallated complexes [Au(N,C)Cl2], The process with phpy is illustrated in Scheme 21. 

The first examples for the oxidative addition of 2-chloro thiazoles to complexes of cf or metal centers were reported by Roper et al. more than 30 years ago [107, 108]. In 2001 Cavell and Yates showed by detailed experimental studies supported by DFT calculations that the oxidative addition of the C2-X bond of imidazolium... 

Despite the weak basicity of isoxazoles, complexes of the parent methyl and phenyl derivatives with numerous metal ions such as copper, zinc, cobalt, etc. have been described (79AHC(25)147). Many transition metal cations form complexes with imidazoles the coordination number is four to six (70AHC(12)103). The chemistry of pyrazole complexes has been especially well studied and coordination compounds are known with thiazoles and 1,2,4-triazoles. Tetrazole anions also form good ligands for heavy metals (77AHC(2l)323). 

Complexes of the stoichiometry [ML3] [C104]2 [L = thiabendazole (65)] contain the metal in an octahedral coordination with the chelating ligand coordinated via the nitrogens of the imidazole and thiazole rings.465... 

Chelate complexes of the same metal salts are formed with 2-(2-pyridyl)thiazole, 4-(2-pyridyl)thiazole and 2,4-bis(2-pyridyl)thiazole. All these complexes are invariably metal-nitrogen coordinated. 

Lappert developed the thermolysis of an electron-rich olefin in the presence of a transition metal complex as another way to synthesise these compounds [4], When, in 1975, Clarke and Taube published their findings on carbon coordinated purine transition metal complexes [5], transition metal NHC complexes with functionalised NHC made their debut in biochemistry. The chemistry of carbenes from natural products became firmly established following the discovery that the catalytic activity of thiamine (vitamin Bl) is based on the intermediate formation of a carbene derived from thiazole [6-9] (see Figure 1.2). 

Given that thiazole is the active centre in vitamin Bl, thiamine has been the centre of intense research of its organocatalytic potential for decades it might be surprising that only very few examples of transition metal NHC complexes are known that use thiazol-2-ylidene or its benzo-annulated analogue benzothiazol-2-ylidene. As we have seen above, one major reason is the instability of the free carbene leading to dimerisation instead. Another major contribution is the apparent inability of thiazol-2-ylidene to coordinate to silver(I) [39] making carbene transfer from silver salts to other transition metals impossible. 

Instead, only two reaction pathways are used to generate transition metal NHC complexes with thiazol-2-ylidene orbenzothiazol-2-ylidene (i) thermal cleavage of an electron-rich olefin in the presence of a suitable transition metal (see Figure 6.12) [40,41] and (ii) deprotonation of a thiazolium or benzothiazolium salt in the presence of a transition metal (see Figure 6.13) [40,42-44]. 

Raubenheimer et al. have developed a third route for transition metal NHC complexes with thiazol-2-ylidene, benzothiazol-2-yUdene and even isothiazol-5-ylidene ligands [45 9]. This method uses a thiazolyl transfer from lithium to a transition metal with subsequent protonation [47,49-54] or alkylation [41,45,46,48,51-56] of the nitrogen atom to generate the transition metal NHC complex. In this way, carbene complexes of copper(I)... 

First-principles calculations have been performed to study the electronic band structure and the magnetic properties for thiazole complex, Fe(thiazole)2Cl2. From the total and the partial density of states and the atomic spin magnetic moments, it was found that Fe(thiazole)2Cl2 is a metallic antiferromagnet and has a half-metallic (HM) ferromagnetic metastable state <2006PLE245>. 

When a metal ion such as nickel (II) is absent, thiazoles and mercaptals are formed. Such reactions have been carried out in which the diketone was biacetyl, 2,3-pentanedione, 2,3-octanedione, l-phenyl-l,2-propane-dione, and 1,2-cyclohexanedione (51). In like manner, the tris complexes of W,W -dimethyl-2,3-butane diimine with iron(II), cobalt(II), and nickel(II) may be prepared from methylamine and biacetyl when the appropriate metal ion (27j 28j 41) is present. Replacing methylamine with hydroxylamine causes the formation of a-dioximes (13). 

Moreover, aryl-oxazoles, -imidazoles [17], or-thiazoles [18], anhydrides [19], and imides [20] are accessible via intramolecular Heck-type carbonylations. In addition to typical acid derivatives, aldehydes [21], ketones [22], aroyl cyanides, aroyl acetylenes, and their derivatives [23] could be synthesized via nucleophilic attack of the acyl metal complex with the corresponding hydrogen or carbon nucleophiles. Even anionic metal complexes like [Co(CO)4] can act as nucleophiles and lead to aroylcobalt complexes as products [24]. 

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