Chiral Metal Complexes with the Biologically Active (+)‐Pilocarpine Ligand: [MCl₂(κN‐(+)‐pilocarpine)₂] (M = Co, Cu)

Abstract

The enantiopure ligand (ϩ)-pilocarpine [(3S,4R)-3-ethyldihydro-4-((1-methyl-1H-imidazol-5-yl)methyl)furan-2(3H)-one] from the chiral pool coordinates with the imidazole nitrogen atom to transition metal atoms. Complexes [MCl 2 (κN-(ϩ)-pilocarpine) 2 ] (M ϭCo, Cu) crystallize as pseudo-tetrahedral (M ϭ Co) or distorted in-between tetrahedral and square-planar (M ϭ Cu) molecules. Supramolecular C-H···Cl contacts are seen in the crystal packing. In aqueous solution the tetrahedral cobalt complex expands its coordination sphere to pseudo-octahedral through the addition of two water molecules as indicated by the reversible color change between blue (solid, non-aqueous solution) and pink.

Synthesis of brookite TiO2 nanorods with isolated Co(ii) surface sites and photocatalytic degradation of 5,8-dihydroxy-1,4-naphthoquinone dye

“…S2 †). The UV-visible spectrum of the supernatant shows similar features to those of pseudo-octahedral Co(II) complexes 73,74 and matches the spectrum of supernatant formed on decomposition of Co 2 (CO) 8 under identical conditions without TiO 2 NR seeds. The bluish precipitate easily re-dispersed in non-polar solvent such as hexanes.…”

Synthesis and Characterization of 4‐, 5‐, and 6‐Coordinate Tris(1‐ethyl‐4‐isopropylimidazolyl‐κN)phosphine Cobalt(II) Complexes

“…Furthermore, the UV/Vis spectrum of 2 is similar to the spectrum of a distorted tetrahedral cobalt(II) compound featuring two imidazole ligands and two chloride ligands. [37] Although the UV/Vis spectra of 2 and 3 are minimally affected if measured in CH 3 CN, the band locations and intensities for 1 change dramatically and are consistent with high-spin Co II in octahedral geometry ( Figure 6). [37] DFT calculations were performed for compounds 1-4 in the gas phase to fully optimize the ground-state structures.…”

“…[37] Although the UV/Vis spectra of 2 and 3 are minimally affected if measured in CH 3 CN, the band locations and intensities for 1 change dramatically and are consistent with high-spin Co II in octahedral geometry ( Figure 6). [37] DFT calculations were performed for compounds 1-4 in the gas phase to fully optimize the ground-state structures. Energies for 1, 2, and 4 were calculated by using PBE0/ 6-31G* methods, whereas for complex 3, PBE0/LanL2DZ methods were used.…”

“…[37,40,41] Retention of coordination number and geometry in CH 2 Cl 2 for 1-3 is supported by an experiment in which Co(OTf) 2 · 2CH 3 CN, CoCl 2 , and CoBr 2 are titrated with 3, 2, and 2 equiv. of 1-ethyl-4-isopropylimidazole in CH 2 Cl 2 , respectively ( Figure S1, Supporting Information).…”

“…[26] The lengths of the Co-N Im bond in 2 [2.004(4), 2.000(4) Å] are shorter relative to those in other cobalt(II) complexes exhibiting tetrahedral geometry with two imidazole nitrogen atoms and two chloride ligands (2.011-2.045 Å). [33,36,37] The Co-Cl bond lengths [2.2479 (15) The unexpected coordination mode in [(4-TIPO iPr )-CoCl 2 ] was explained by decreased electron density at the imidazole nitrogen atom as a result of the electron-withdrawing effect of the phosphine oxide group. This observation is supported by the fact that the phosphine derivative exhibits κ 3 N coordination in the presence of chloride groups.…”