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Keywords:

  • Metallacycles;
  • Alkynes;
  • Metallo­cenes;
  • Sulfur;
  • Reaction mechanisms

Abstract

Reactions of the group 4 metallocene alkyne complexes [Cp2M(L)(btmsa)] (Cp = η5-cyclopentadienyl = η5-C5H5, btmsa = η2-Me3SiC2SiMe3; 1: M = Ti, L = none; 2: M = Zr, L = pyridine) and of the [(triphos)CoI] moiety [triphos = 1,1,1-tris(diphenylphosphanylmethyl)ethane] with the benzylsulfanyl-substituted acetylenes PhCH2S–C2–SCH2Ph (3) and PhCH2S–C2–SFmoc (4) (Fmoc = fluorenylmethoxycarbonyl) have been investigated. Complex 1 reacted with 3 to give a mixture of a violet solid and [Cp2Ti(SCH2Ph)2] (5). Subsequently, the violet solid transformed in toluene at 70 °C into the dinuclear complex [(Cp2Ti)2(μ-κ22-BnSC4SBn)] (6) displaying two [Cp2Ti] moieties bridged by a 1,4-bis(benzylsulfanyl)-1,3-butadiyne in the trans configuration. Complex 6 was further degraded in toluene at 100 °C to the tetranuclear cluster [CpTiS]4 (7). Similar reactivity was deduced indirectly for the reaction partners 1/4 and 2/3. For CoI, the side-on alkyne complexes [(triphos)Co(3)](PF6) (9-PF6) and [(triphos)Co(4)](PF6) (10-PF6) were obtained. Reductive removal of the benzyl groups in 9-PF6 and subsequent coordination of the [Cp(PPh3)RuII]+ moiety led to the dinuclear complex [(triphos)Co(μ-η22-C2S2)RuCp(PPh3)] (13) displaying acetylene dithiolate (acdt2–) in a side-on carbon–sulfur chelate coordination mode. In contrast, the reaction of 10-PF6 with piperidine under very mild conditions resulted in the thio-alkyne complex [(triphos)Co(PhCH2SC2S)] (11) bearing a terminal sulfur substituent at the coordinated alkyne. However, a subsequent rearrangement reaction led to the CoIII dithiolene complex [(triphos)Co{S2C2(NC5H10)(CH2Ph)}](PF6) (14-PF6). The intricate rearrangement very likely involves a dinuclear Co species with a η22 coordination of the C2S2 moiety.