Activation of the Carbon−Sulfur Bonds in Benzothiophenes by Precoordination of Transition Metals to the Carbocyclic Ring

Abstract

Listen

Translate article

Coordination of an electrophilic transition-metal fragment, MLn, to the carbocyclic ring of benzothiophene (BT) to form (η6-BT)MLnm+ activates a C−S bond to cleavage by the weak nucleophile Pt(PPh3)3, with concomitant insertion of Pt(PPh3)2. The rate of formation of the resulting metallathiacyclic insertion products, {(η6-BT·Pt(PPh3)2}MLnm+, depends on the metal fragment in the order MLn = Ru(C6Me6)2+, Mn(CO)3+ > FeCp+, RuCp+ ≫ Cr(CO)3, with no reaction occurring in the absence of a MLn activating group. All of the unsubstituted benzothiophene complexes undergo regiospecific cleavage of the olefinic C−S bond rather than the aryl C−S bond, which is likely a consequence of steric congestion that would exist if insertion had occurred at the latter site. The X-ray structures of the metallathiacycles {(η6-BT·Pt(PPh3)2}Mn(CO)3+ and {(η6-BT·Pt(PPh3)2}FeCp+ are reported. The complexes (η5-2,5-dimethylthiophene)Mn(CO)3+ and (η6-dibenzothiophene)Mn(CO)3+ also undergo rapid C−S bond cleavage with metal insertion in ...