We are developing bimetallic platforms for the cooperative activation of heteroallenes. Toward this goal, we synthesized open-chain and macrocyclic dinucleating ligands featuring different linkers (1,3-xylylene diamine, 1,4-xylylene diamine and xanthene) and different chelating units (iminopyridine and bis(imino)pyridine). Dinucleating bis(iminopyridine) ligands L1 react with Ni(COD)2 to form Ni2(L1)2 complexes (irrespective of the metal-to-ligand ratio) or Ni2(L1)(COD)2 as a function of the steric and electronic properties of the ligand precursor. Product structures disclose an anti geometry in the Ni2(L1)(COD)2 species and helical (anti) structures for Ni2(L)2 complexes. Carbon disulfide adducts Ni2(L1)(CS2)2 were obtained in good yields upon addition of CS2 to Ni2(L1)(COD)2, or in a one-pot reaction of L with two equivalents of both Ni(COD)2 and CS2. The complexes feature square-planar Ni(II) metal centers ligated by fully oxidized iminopyridine and [CS2]2�. Ni2(L1)(CS2)2 complexes are highly flexible, displaying both syn and anti conformations (shortest S---S separation of 5.0 � and 9.5 �, respectively) in the solid state. DFT calculations demonstrate virtually no energy difference between the two conformations. Electrochemical studies of the Ni2(L1)(CS2)2 complexes display two ligand-based reductions, and a broad CS2-based oxidation. Chemical oxidation with [FeCp2]+ liberated free CS2. Macrocyclic ligands L2 were obtained via template synthesis with oxalate as a template. Studies concerning oxalate removal and electrochemical reactivity in the presence of carbon dioxide will be reported. 

Dinuclear metal complexes for the cooperative activation of heteroallenes

246th National Meeting (2013)

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