Thiophene, metallation structure

Metal complexes containing q -bonded thiophenes, where the ring formally donates 6 electrons and occupies three coordination sites (Lj-type ligand) are the most numerous and stable of the transition metal-thiophene derivatives, examples being available for Cr, Mn, Re, Fe, Ru, Rh, and Ir. Curiously, the synthesis of the first n-thiophene metal complex, viz. Cr(CO)3(q -T) reported by Fischer as early as 1958 [67] represents still today the only example available for a Group 6 metal it-bonded to thiophene its X-ray structure was solved by Dahl in 1965 albeit with a strong rotational disorder for the... 

The study of hydrodesulfurization (HDS) has had tremendous impact on the petroleum industry <88ACR387, 88ACR394). The mechanism of hydrodesulfurization has theoretical and commercial importance and has been the subject of numerous reports investigating mechanism, variation of catalyst and substrate, and product composition. In general, the role of the metal catalyst as well as the structures of thiophene-metal coordination complexes will be discussed in Section 2.12.11.2. In this section, we focus on specific desulfurization to produce isolable products. 

Ziemels, K. E., Hussain, A. T Bradley, D. D. C., Friend, R. H., Ruhe, J., and Wegner, G., Optical spectroscopy of field-induced charge in poly(3-hexyl-thiophene) metal-insulator-semiconductor structure evidence for polarons, Phys. Rev. Lett., 66, 2231-2234 (1991). 

A limited number of non-transition-metal derivatives of thiophene will be considered in this subsection. There are no short-range contacts between the lithium atoms originating from the (LiO)6 cores and the sulfur atoms in [Li—O—EMc2 (2-C4H3S)]6 (E = C, Si) (97OM5032), and evidence for Tr-interactions can be found in the X-ray crystal structures of these compounds. Theoretical computations show that a- (S ) Li" " interactions are weak, whereas Tr-Li" contributions are considerable, in accord with the general reasoning on the electronic characteristics of uncomplexed thiophene. 

Figure 9.11 Thiophene adsorbed at 500 K on an H-atom pretreated MoS2 cluster (50 x 54 A2). Beam-like features at the metallic edge [scan line (i)] and the shifted intensity of the outermost edge protrusions relative to the clean edge (triangles refer to the clean edge). These shifts in intensity [line scan (ii)] are associated with changes in the local electronic structure after adsorption of thiophene observed with STM. All the images were taken at room temperature subsequent to thiophene adsorption at 500 K. (Reproduced from Ref. 34).

Synthesis AND Structural Characterization of Thiophene-Functionalized Metal Dithiolenes... 

Short intramolecular S -S contacts ranging between 3.159 and 3.223 A are observed between the external thiophenes and the coordinating sulfur atoms of the dithiolene. These contacts are shorter than the sum of the corresponding van der Waals radii (3.60 A) and shorter than the various S -S contacts exhibited by the previous structures discussed above. However, unlike all of the previous structures, no significant intermolecular interactions were observed between the metal thiophenedithiolene anions of 7a or... 

The nonplanar nature of 11 hinders intermoleeular contacts between the metal dithiolene complexes. Thus, there are few intermoleeular interactions between the anions within [Et4N][ll], although short C-H -S contacts of 2.906 A are observed between the pendent thiophenes of neighboring anions (Figure 13A). In contrast, the more planar structure of 12 allows significant jt stacking of the complexes to form columns with a face-to-face distance of 3.7 A (Figure 13B). ... 

The remaining two related structures of [Et4N][14] and 17 exhibit similar features. The anion 14 adopts a structure similar to 12 with the thiophenes near planar (dihedral of 9.0 ) and the phenyl rings near perpendicular (dihedral of 79.6°). The bond between the thiophenes and the dithiolene core is 1.472 A, roughly the same as the two previous structures. No significant intermoleeular interactions were observed between the metal thiophenedithiolene anions. 

The observed spectra of some duroquinone-nickel complexes with olefins have been correlated by means of semiquantitative molecular-orbital theory by Schrauzer and Thy ret (48). In the case of n complexes of polynuclear hydrocarbons, such as naphthalene and anthracene, although their spectra are recorded, no conclusions have been drawn with regard to structure nor has any theoretical work been reported. Similar remarks apply to complexes of nonalternant hydrocarbons such as azulene. Although innumerable complexes of olefins with various transition metals are known and admirably reviewed (84), no theoretical discussion of even a qualitative nature has been provided of their electronic spectra. A recent qualitative account of the electronic spectra of a series of cyclopentadienone, quinone, and thiophene dioxide complexes has been given by Schrauzer and Kratel (85). 

One curious observation is that high activities for direct sulfur extraction from thiophene derivatives are only exhibited by metal sulfides that form stacked lamellar crystallites, similar to graphite structures (1-3). MoS2 is classic in this regard and has found applications as a high-temperature lubricant with properties very similar to those of graphite. The other widely used metal sulfide in HDS is WS2, which also forms lamellar crystal struc-... 

Not all clathrates are hydrates. Other well-known examples have host lattices formed from hydrogen bonded aggregates of hydroquinone, phenol, and similar organic compounds. Non-hydrogen bonded host structures are also known. One example is a cyclotriphosphazene. (C6H402PN). that traps molecules such as benzene in tunnels in the crystal.2 In addition, coordination polymers are formed by ambidentate ligands, such as CN and SCN, which coordinate to metal ions at both ends (Chapter 12). Perhaps the best known of this type of compound is the series of Ni(CN)2NHj M compounds, where M may be benzene, thiophene, furon. pyrrole, aniline, or phenol. 

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