Benzothiophene complexes

Thiophene complexes, containing a(S)-coordination bond, are represented by a high number of structures [8,13,205b,622,623]. Compound 321 [8] is an example of these complexes. (a-S-Coordination is also characteristic for benzothiophene complexes, for instance 322 [8,13,624] ... 

JA5190). Upon deprotonation by bases, 285 (R = H) transforms to 286, and 285 (R = Me) goes to 287 because the C2 position is occupied. Protonation of 286 with triflic acid occurs at position 3 of the heteroring to form the benzothienyl carbene complex 288, and deprotonation reverts it to 286. This kind of process is a rarity for the uncomplexed benzothiophenes (81AHC171). 

Several heteroaromatic compounds can be hydrogenated by [Rh(COD) (PPh3)2]+ species. Thus, this cationic complex has been reported to be a catalyst precursor for the homogeneous hydrogenation of heteroaromatic compounds such as quinoline [32] or benzothiophene [33]. Detailed mechanistic cycles have been proposed by Sanchez-Delgado and coworkers. The mechanism of hydrogenation of benzothiophene by the cationic rhodium(III) complex, [Rh(C5Me5) (MeCN)3]2+, has been elucidated by Fish and coworkers [34]. 

The combination of [IrCl(cod)Cl]2 complex with P(t-Bu)3 efficiently catalyzes aromatic homologation using internal alkyne [70]. For example, the reaction of benzoyl chloride 153 with 4-octyne 154 afforded 1,2,3,4-tetrapropylnaphthalene 155 (Equation 10.41). The reaction with 2-thenoyl and 2-naphthoyl chlorides also affords benzothiophene and anthracene, respectively, in high yields. The reaction would proceed as follows (Scheme 10.9) (i) oxidative addition of aroyl chloride... 

Electron donation by potential carcinogens, such as 2-acetylaminodi-benzothiophene, has been estimated from the strength of their charge-transfer complexes with chloranil in acetonitrile. - In this context it should be noted that the hydrogen bonding of phenol to the 77-electrons of dibenzothiophene has been studied and that a thiourea adduct has proved useful in the removal of dibenzothiophene from oil. - ... 

A similar analysis has been done91 on CT-complexation of the series benzene, benzothiophene, benzo[l,2-b, 4,3-b ]dithiophene ([3]SBS), and the homologs [5]SBSBS and [7]SBSBSBS with TCNQ as the acceptor. Beside association constants, also AH- and AS-values were determined by measurements at different temperatures (Table 21). It is striking that the gradual increase of the association constant in the series is interrupted at [5]SBSBS the next member has even a lower value. 

In the second example carbon monoxide insertion into a benzothiophenylpalladium complex, and a subsequent C-H activation led to the transformation of 3-iodo-2-phenyl-benzothiophene to the tetracyclic compound shown in 5.9.9... 

Several of these metal complexes that readily form metallathiabenzenes have been shown to be true homogeneous catalysts for the conversion of benzothiophene to ethylbenzene (4). Pathway IV has been demonstrated only for thiophenes and substituted thiophenes. Pathway V has not been demonstrated but could be involved in reactions conducted in the presence of acids. This point is expanded later because of the potential involvement of acidic -SH groups on HDS catalysts. 

This statement could well be expanded to include studies describing the kinetics of model compounds. In reviewing the literature, one finds that there are almost as many kinetic representations as there are researchers and/or model compounds. Even the same authors have found it necessary to use different equations to describe the different responses to inhibitors for closely related sulfur species such as thiophene, benzothiophene, and dibenzothiophene (104, 122, 123). The inhibiting effect of H2S for the hydrogenation of a simple molecule, such as toluene, has been found to require extremely complex equations to adequately describe mathemati-... 

In the thiophene (75JHC327) and benzothiophene (78JOC4379) series, nucleophilic substitution of hydride ion (Scheme 31) becomes possible due to the ability of 3d-orbitals of the sulfur atom to stabilize negative charge arising in the anionic cr-complex. 

A number of reactions have been investigated which could form a thiophene ring by forming a bond y to the sulfur atom, but which have not been generalized. Photocyclization of phenylthioethylenes has led to benzothiophenes, usually in low yields, and sometimes accompanied by rearrangement (68JOC2218). Irradiation of (115 R = H or Me, and R1 = Ph) in the presence of iodine gave a mixture of (116) and (117) in about 11% maximum yield. If R1 = H or Me, no product (117) was found, and if R was Ph, only traces of cyclized products were detected. A complex mechanism was proposed to account for these results. 

J-Bonded metal complexes, hydrodesulfurization models with benzothiophene, 1, 769 with dibenzothiophene, 1, 769 Bonding studies energetics, 1, 285 overview, 1, 573—603 ring size effects, 1, 396 strength, 1, 609... 

---