Low-Valent Ruthenium Complexes of the Non-innocent 2 , 6-Bis ( imino ) pyridine Ligand

  • Gallagher M
  • Wieder N
  • Dioumaev V
 et al. 
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A series of low-valent ruthenium complexes bearing 2,6-bis(imino)pyridyl (“[N3]”) ligands has been synthesized and characterized. Reduction of [N3]RuCl2(C2H4) ([N3 xyl]=2,6-(XylNCMe)2- C5H3N, 1a; [N3 mes]=2,6-(MesNCMe)2C5H2N, 1b; [tBu-N3 mes]=2,6-(MesNCMe)2p-tBuC5H2N, 1c) with hydridosilanes in an arene solvent such as toluene yields new 18e- η6-arene complexes [κ2-N3]Ru(η6-MeC6H5), 2a,b,c, in which the [N3] ligand is bidentate and only one imine group is coordinated to the metal. The arene ligand can be displaced with dinitrogen in non-arene solvents to yield the binuclear, four-coordinate, formally Ru(0) complexes {[N3]Ru}2(μ-N2), 3a,b,c. Pyrophoric complex 3c is a rare example of a structurally characterized Ru(0) dinitrogen complex. Treatment of low-valent complexes 2 or 3 with donor ligands generates five-coordinate complexes [N3 xyl]RuL1,2 (L1,2=C2H4, 4a; L1,2=PMe3, 5a; L1,2=CO, 6a; L1=PMe3, L2=CO, 7a). Complexes 2a, 3c, 5a, 6a, and 7a are diamagnetic and have been structurally characterized by single-crystal X-ray diffraction methods. New six-coordinate Ru(II) complexes [N3 xyl]RuCl2(L) (L=PMe3, CO) were also isolated and structurally characterized. The infrared data, observed geometrical parameters, and reactivity patterns of the formally Ru(0) centers suggest varying degrees of electron delocalization to the “non-innocent” bis(imino)pyridyl, but probably not to the extent implied by the valence tautomeric [N3]2-/Ru(II) canonical form. Although the [N3]-/Ru(I) representation may portray the electron distribution more accurately than “Ru(0)”, the inherent odd electron counts on both ligand and metal;and requisite antiferromagnetic coupling;provides little in the way of “useful” distinctions or predictive value for the low-valent [N3]Ru(L)2 complexes with strong-field co-ligands such as CO and PMe3. These five-coordinate adducts seem to be adequately described as Ru(0) complexes of the neutral [N3] ligand. However, “non-innocent” valence tautomeric canonical forms such as [N3]-/Ru þ may be more applicable to the four-coordinate dinitrogen complexes {[N3]Ru}2(μ-N2).

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  • Michelle Gallagher

  • Noah L. Wieder

  • Vladimir K. Dioumaev

  • Patrick J. Carroll

  • Donald H. Berry

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