A Cu(II)-Mediated C−H Oxygenation of Sterically Hindered Tripyridine Ligands To Form Triangular Cu(II)₃ Complexes

Abstract

Two sterically hindered tris-pyridyl methane ligands, tris(6-methyl-2-pyridyl)methane (L1) and bis(6-methyl-2-pyridyl)pyridylmethane (L2), are newly synthesized. Under aerobic conditions, Ln (n = 1 or 2) reacts with CuX2 (X = Cl or Br), oxygenated at the methine position to LnOH or LnOMe. The former alcoholate ligand creates trinuclear Cu(II) complexes [Cu3(X)(LnO)3](PF6)2 [(X, n) = (Br, 1) 1, (C1, 1) 2, (Br, 2) 3, or (C1, 2) 4] in which the alkoxide oxygen atoms bridge copper centers. The crystal structures of 1-4 are presented along with their magnetic susceptibility data. The weak antiferromagnetic coupling between the Cu(II) centers in this trinuclear arrangement is due to weak interaction of the magnetic orbitals (dz2) which are oriented along three alternate sides in a hexagon of the Cu3O3 core in 1-4. Under anaerobic conditions, L1 reacts with CuBr2 to form a square pyramidal complex [CuL1Br2] (9) with the ligand facially capping. [Cu(Br)2(L1OMe)] (10) was obtained after the suspension of 9 in MeOH was stirred under air for 48 h. In the presence of cyclohexene, 9 is converted to [Cu(Br)(L1)]m (m = 1 or 2) 5 quantitatively to give trans- 1,2-dibromocyclohexane, indicating that Br2 is generated during the reaction. The FAB MS spectrum of [18O]-1 prepared by the reaction of L1 with CuBr2 under 18O2 shows that the ligand of [18O]-1 is L1(18O-.) L1(18OH), L1OCD3, and bis(6-methyl-2-pyridyl) ketone were obtained from reaction of L1 with CuBr2 in CD3OD under 18O2. These results indicate that the origins of the O atom in L1OH and L1OMe are O2 and MeOH, respectively. On the basis of these results, a mechanism of the oxygenation of L1 in the present system will be proposed.

Trinucleating Copper: Synthesis and Magnetostructural Characterization of Complexes Supported by a Hexapyridyl 1,3,5‐Triarylbenzene Ligand

“…Alkoxo‐bridged tricopper(II) clusters with similar [Cu 3 O 3 ] motifs are known, but generally form by self‐assembly of mononuclear copper(II) moieties 12a. 13 The magnetic behavior of these complexes has been studied because spin‐frustrated triangular complexes may exhibit interesting ground states.…”

“…13 The magnetic behavior of these complexes has been studied because spin‐frustrated triangular complexes may exhibit interesting ground states. It has been shown that varying the anion bridges of linear14 and triangular15 trinuclear copper(II) complexes changes the magnetic coupling, but no systematic study has been reported of these effects on μ‐alkoxo‐bridged trimers lacking a strongly μ 3 ‐coordinated ligand 12a. 16 Since the synthesis of anion variants of the tricopper(II) complexes supported by the trinucleating ligand L described above is facile, a magnetostructural investigation of the effect of the capping anion the [Cu 3 O 3 N 6 ] core was performed.…”

Toward an Allosteric Metallated Container

“…An increase in the 360 nm band suggests interaction of the free pyridyl groups with Fe, but the L 1 :Fe stoichiometry is not compatible with a binding of just a second Fe 2+ ion to the tris(pyrid-2yl) site in the interior of the cage. Rather, the OH group in L 2 might act as a bridging ligand {as observed for the Cu 2+ ions in the related complex [Cu 3 (Br)(L) 3 ](PF 6 ) 2 , [21] where L = tris(6-methyl-2-pyridyl)methanol}, for up to three Fe II ions with additional coordination by one pyridyl group each and located at the exterior of the cage. sharp signals increases and that of the broad signals decreases.…”

Reversible O2-Binding and Activation with Dicopper and Diiron Complexes Stabilized by Various Hexapyridine Ligands. Stability, Modulation, and Flexibility of the Dinuclear Structure as Key Aspects for the Dimetal/O2 Chemistry

“…[64][65][66] We found that copper complexes with sterically hindered tripyridine ligands can be structurally modulated by introducing an alkyl group at the bridgehead position of the ligand. 67 We prepared three sterically hindered tripyridine ligands: tris-(6-methyl-2-pyridyl)methane (H6M3t), 68 1,1,1-tris(6-methyl-2-pyridyl)ethane (Me6M3t), 67 and 1,1,1-tris(6-methyl-2-pyridyl)propane (Et6M3t). 67 The chemical structures of H6M3t, Me6M3t, and Et6M3t are shown in Chart 4.…”