Models for the Homogeneous Hydrodesulfurization of Benzothiophenes. Carbon−Sulfur Bond Cleavage, Hydrogenolysis, and Desulfurization Reactions Mediated by Coordination of the Carbocyclic Ring to Manganese and Ruthenium

Abstract

Chemical reduction of a series of (η6-benzothiophene)Mn(CO)3 + complexes (10a−c) under CO affords neutral dimanganese metallathiacyclic complexes (12a−c), which have a Mn(CO)4 moiety inserted into the C(aryl)−S bond. Reduction of (η6-benzothiophene)Ru(C6Me6)2+ in the presence of CO and (η6-1-Me-naphthalene)Mn(CO)3 + affords an analogous cationic bimetallic (15), which is converted to a neutral cyclohexadienyl complex (16) by hydride addition to the carbocyclic benzothiophene ring. The sulfur atom in the metallathiacyclic ring in 12 and 16 is nucleophilic and reacts with electrophiles CF3SO3Me, HBF4, and W(CO)5(THF) to afford complexes such as 6, 14, and 17. Treatment of 12 with H2 results in hydrogenolysis of the Mn−C σ bond and formation of the bimetallic Mn2(CO)8(H)(SCHCHPh) (8), which contains a Mn−Mn bond and bridging hydride and thiolate ligands. Reaction of 6 and 17 with H2 results in desulfurization of the benzothiophene and formation of a mixture of Mn(CO)5SR and [Mn(CO)4SR]2 (R = H, Me). Crystal structures are reported for 9 (R = Me), 12b, and 16.

Comparative Study for the Cobalt(II)- and Iron(II)-Mediated Desulfurization of Disulfides Demonstrating That the C–S Bond Cleavage Step Precedes the S–S Bond Cleavage Step

“…It is interesting to note that hydrosulfide units have been proposed to be involved in the HDS process. Moreover, transition-metal–hydrosulfide complexes have often been isolated as possible intermediates during the cleavage of C–S bonds in different transition-metal–thiolate complexes. − Consequently, transition-metal-mediated C–S bond cleavage of organosulfur substrates is being actively pursued by several research groups. − Along the same line, Ni(0)-mediated cleavage of C–S and S–S bonds of alkyl/aryl sulfoxides and disulfides, respectively, has been reported in the literature. The coordination of Mo with organosulfur compounds followed by C–S bond cleavage is also available in the literature. − However, most such reports involve the intramolecular C–S bond cleavage of coordinated ligands and metal insertion in C–S bonds, instead of a complete desulfurization of the substrate.…”

Transition Metal Complexes of Chromium, Molybdenum, Tungsten, and Manganese Containing η1(S)-2,5-Dimethylthiophene, Benzothiophene, and Dibenzothiophene Ligands

“…Recent examples include Cp*(CO) 2 Re(η 1 (S)-T*), 19,22 [Cp(NO)(PPh 3 )Re(η 1 (S)-T*) + ], 23 [(η 5 -T)Mn(CO) 3 + ], 24 [(η 6 -DBT)Mn(CO) 3 + ], 25 and [(η 6 -BT)-Mn(CO) 3 + ], 26 as well as several C,S-cleaved products. 27,28 We now report the preparation of group 6 and 7 metal complexes of 2,5-Me 2 T, BT, and DBT obtained by UV irradiation of hexanes solutions containing M(CO) 6 or CpMn(CO) 3 and excess T* ligands. X-ray-determined molecular structures are reported for three complexes.…”

“…Group 7 metals also form complexes containing coordinated thiophene ligands. Recent examples include Cp*(CO) 2 Re(η 1 ( S )-T*), , [Cp(NO)(PPh 3 )Re(η 1 ( S )-T*) + ], [(η 5 -T)Mn(CO) 3 + ], [(η 6 -DBT)Mn(CO) 3 + ], and [(η 6 -BT)Mn(CO) 3 + ], as well as several C,S-cleaved products. , …”

Carbon−Carbon Bond Activation in Biphenylene. Effect of η6-Coordination to Manganese Tricarbonyl

“…This means that the reaction half-life must be less than 30 s. Hence, it may be concluded that the Mn(CO) 3 + moiety in eq 2 decreases the reaction half-life by many orders of magnitude. In an analogous manner, coordination of Mn(CO) 3 + to the carbocyclic ring in the stable heterocycles benzothiophene and benzofuran has been shown to greatly accelerate metal insertion into the C−S and C−O bonds, respectively. −

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