Thioethers metal complexes

Coordination chemistry of thioethers, selenoethers and telluroethers in transition metal complexes. S. G. Murray and F. R. Hartley, Chem. Rev., 1981, 81, 365-414 (748). 

Azoresorcinol, pyridyl-metal complexes dyes, 6, 74 Azurins, 6, 651, 652 copper(II) complexes, 2, 772 5, 721 electron transfer reactions, 6, 653 NMR, 6, 652 Raman spectra, 6, 652 spectra, 6, 652 thioether complexes, 2, 557 Azurite... 

In contrast to the large number of chiral pyridine derivatives used as ligands of metal complexes in asymmetric catalysis, only a few examples of chiral sulfur-containing pyridine ligands have so far been reported, such as pyridine thioethers derived from ( + )-camphor depicted in Scheme 1.33, which were assessed in the test reaction providing enantioselectivities of up to 76% ee. The related 2,2 -bipyridine thioethers were also prepared but showed a lower stereodilferentiating capability in the test reaction. 

In 2007, Fernandez et al. demonstrated that transition-metal complexes with heterobidentate S/C ligands based on imidazopyridin-3-ylidene and thioether functionalities could be readily prepared from the corresponding azolium salts by reaction with Ag20 and transmetalation of the resulting silver carbenes with appropriate metal sources. The cationic Pd(allyl)(carbene-S) complexes have proven to be active catalysts in the test reaction, reaching enantioselectivities of... 

Sargeson and co-workers have prepared a series of thioether-containing cage ligands, typically using template reactions. Transition metal complexes of these compounds exhibit interesting properties and the extremely robust nature of... 

The ability of thioether macrocyclic complexes (and especially those of [9]aneS3) to support multi-redox behaviour at the coordinated metal centre is particularly notable. This allows a series of reversible stepwise one-electron oxidation and/or reduction processes, and stabilization of highly unusual transition metal oxidation states e.g. mononuclear [Pd([9]aneS3)2]2+/3+/4+,149 [Au([9]aneS3)2]+/2+/3+,150 [Ni([9]aneS3)2]2+/3+,151 and [Rh([9]aneS3)2]+/2+/3+.152 It appears to be the ability of the crown thioethers to readily adjust their... 

A review article has appeared (237) which discusses the biological activity of thioethers and their derivatives with particular reference to interactions with transition-metal ions. Accordingly, only some of the more salient points will be discussed here. In any biological studies, the toxicity of Me2SO 482) and of its transition-metal complexes 140) should be borne in mind. 

Finally, other chiral donor atoms, P,As (see Problem 9) and in metal complexes have been less systematically studied than nitrogen. Inversion rates in metal ion-thioether complexes have been measured by nmr, but the species are too labile to allow a successful resolution. 

Chiral sulfoxides have emerged as versatile building blocks and chiral auxiliaries in the asymmetric synthesis of pharmaceutical products. The asymmetric oxidation of prochiral sulfides with chiral metal complexes has become one of the most effective routes to obtain these chiral sulfoxides.We have recently developed a new heterogeneous catalytic system (WO3-30% H2O2) which efficiently catalyzes both the asymmetric oxidation of a variety of thioethers (1) and the kinetic resolution of racemic sulfoxides (3), when used in the presence of cinchona alkaloids such as hydroquinidine 2,5-diphenyl-4,6-pyrimidinediyl diether [(DHQD)2-PYR], Optically active sulfoxides (2) are produced in high yields and with good enantioselectivities (Figure 9.3). ... 

Coordination Chemistry of Thioethers, Selenoethers, and Telluroethers in Transition- 1654 Metal Complexes... 

Both macrocyclic and open-chain cyclic thioethers have been used as ligands. Figure 1 shows a collection of typical examples of macrocyclic species. They offer very flexible coordination behavior and their metal complexes sometimes exist with different electron populations. 

Virtually all types of metal ions have been complexed with macrocyclic ligands.2-7 Complexes of transition metal ions have been studied extensively with tetraaza macrocycles (Chapter 21.2). Porphyrin and porphyrin-related complexes are of course notoriously present in biological systems and have been receiving considerable investigative attention (Chapter 22).8 Macrocyclic ligands derived from the Schiffbase and template-assisted condensation reactions of Curtis and Busch also figure prominantly with transition metal ions.6,7 The chemistry of these ions has been more recently expanded into the realm of polyaza, polynucleating and polycyclic systems.9 Transition metal complexes with thioether and phosphorus donor macrocycles are also known.2... 

One of the simplest and widely used methods of forming C-S bonds involves nucleophilic attack of a thiolate on a suitable C-centred electrophile such as an alkyl halide (Fig. 5-74). Co-ordinated thiolate ligands behave as nucleophiles in exactly the same manner, and the method has been extensively used for the preparation of thioethers and their metal complexes. The method has been particularly commonly utilised in the formation of macrocyclic ligands in templated syntheses (see Chapter 6). 

With establishment of the crystal structure, three major features concerning the electronic structure of the blue copper site can be addressed. These features are 1) the nature of the thiolate and thioether bonds, 2) the nature of the ground state wavefunction and 3) the extent of covalency. We have also become strongly involved in using photoelectron spectroscopy as a powerful approach toward determining covalency in transition metal complexes. These will be discussed in turn. 

Strikingly similar results were obtained for all complexes and revealed a structure-function relationship of [M(L)(S )] complexes that can be summarized as follows Metal thioether thiolate complexes exhibit Brpnsted acid-base behavior and can be reversibly protonated. Thiolate protonation drastically influences electron densities at the metal centers and redox potentials of complexes. However, in all these reactions and electronically changing situations, the metal-sulfur core of a specific [M(S )] complex remains invariant. 

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