No abstract

The great importance of heterogeneous hydrodesulfurization (HDS)"] has spawned numerous studies with homogeneous model systems.I2] Of particular interest has been the activation of derivatives of thiophene (T), benzothiophene (BT), and dibenzothiophene (DBT). While all three of these sulfur-containing molecules are relevant to HDS, the latter two are especially so because they are more difficult to desulfurize and thus are much more abundant in fossil fuels. The key step in HDS is cleavage of the S-C bonds, and a reasonable way for this to occur is by initial coordination to a metal followed by insertion into the S-C bond. In particular, precoordination of the metal to the sulfur atom of the thiophene unit is thought to be crucial to S-C bondIn the case of BT ( I ) , several examples of the insertion of metal fragments ML, into the have been reported ; however, there have been no reports of S-C(aryl) bond cleavage to give 3. The X-ray structurer4] of [(BT)Re(CO),Cp*] (Cp* = C,Me,), in which the rhenium S-C(viny1) bond to give 2 (M = Fe, Ru, Rh, Ir, Pt13b.5361 ) 1 2 3atom is q'-bonded to the sulfur atom. suggests that ql-S coordination selectively weakens the S-C(viny1) bond but not the S-C(ary1) bond, thus providing an explanation16e1 for why 2, and not 3, is formed. Herein we demonstrate that the insertion of a metal atom into the S-C(ary1) bond of BT to give complexes of type 3 can, in fact, be readily accomplished.

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.