Cyclometallation reactions of 6-(2-thienyl)-2,2′-bipyridine with d8 transiton metal ions

Abstract

The potentially terdentate ligand 6-(2-thienyl)-2,2′-bipyridine (Hthbipy) reacts with [MCl₄]^2–(M = Pd or Pt) under mild conditions to give cyclometallated complexes in which the thienyl ring is metallated at the 3 position. The metallated complexes [M(thbipy)Cl](M = Pd or Pt) react with trimethyl phosphite to give phosphonate complexes [M(thbipy){P(O)(OMe)₂}] and with Na[acac](Hacac = acetylacetone) to give [M(thbipy)(acac)] with a C-bonded acac ligand. Under mild conditions, the non-metallated compound [Pd(Hthbipy)Cl₂] can be isolated. In contrast, the reaction of Hthbipy with Na[AuCl₄] at ambient temperature yields the non-metallated complex [Au(Hthbipy)Cl₃], but upon heating this, or performing the reaction at higher temperatures, the metallated compound [Au(thbipy)Cl₂] is obtained. X-Ray structural analysis of this complex reveals it to be dimeric where the ligand has metallated at the 5 position of the thienyl ring and adopts a bridging bidentate N,C mode [triclinic, space group P, a= 9.271(5), b= 14.214(10), c= 16.194(10)Å, α= 108.11(5), β= 96.55(5), γ= 111.46(5)°, Z= 2, R= 0.075, R′= 0.094].