Versatile Chemical Transformations of Benzoxazole Based Ligands on Complexation with 3d-Metal Ions

Abstract

Two benzoxazoles derivative ligands were synthesized from the condensation of 3,5-di-tert-butyl-o-benzoquinone (DTBBQ) with ethanolamine or 1,3-diamino-2-hydroxypropane in methanol. Condensation of DTBBQ with ethanolamine gives the expected 5,7-di-tert-butyl-2-methylenhydroxylbenzoxazole (HL1) while with 1,3-diamino-2-hydroxypropane it gives (2-hydroxyethyl-2-{2,4-bis(1,1-dimethylethyl)-1-phenol-6 amino}-2{5,7-di-tert-butyl-benzoxazole}) (H(2)L2) with only one benzoxazole ring instead of the symmetric bis-benzoxazole derivative. The structure of HL1 and H(2)L2 were confirmed by NMR-spectroscopy and X-ray diffraction on a single crystal for HL1. The reaction of HL1 with CuCl(2) gives a mononuclear [Cu(II)(HL1)(2)Cl(2)] (1) complex for which the crystal structure shows that HL1 is preserved. In contrast, upon reaction with nickel(II), cobalt(II), and manganese(II) H(2)L2 is further oxidized and transformed in new ligands HL3 in mononuclear complexes [M(II)(L3)(2)] (M = Ni(II) (2); M = Co(II) (3)) and H(2)L4 in tetranuclear complex [Mn(II)(4)(HL4)(4)Cl(4)] (4) as found from the crystal structures of complexes 2-4. Electrochemical studies for complexes 2 and 3 evidence complicated redox properties. [Mn(II)(4)(HL4)(4)Cl(4)] (4) has a cubane-like structure with a "4 + 2" fashion The magnetic susceptibility of 4 is well fitted considering one Mn---Mn interaction J(a)(Mn(II)-Mn(II)) = -0.50(1) cm(-1) with g = 2.00(7).

Synthesis, characterization and catalytic activity of copper(ii) complexes containing a redox-active benzoxazole iminosemiquinone ligand

“…In addition, the 1 H NMR data is consistent with a recent report on a similar ligand system. 54 Synthesis and structural characterization of L BIS Cu II X complexes…”

Heterometallic CuII–DyIII Clusters of Different Nuclearities with Slow Magnetic Relaxation

“…8b,9a,b,10,11b,12a,b,d,e,13,15,17b,19−21,23b,24 −26,29 Again, gaining control over the nuclearity of 3d−4f clusters is always challenging. Considering the Cu II −Dy III there are many examples of Cu II −Dy III clusters reported in the literature with large diversity of structural types such as CuDy, 8 CuDy 2 , 9 CuDy 4 , 10 Cu 2 Dy,11 Cu 2 Dy 2 , 12 Cu 2 Dy 7 , 13 Cu 3 Dy 2 , 14 Cu 3 Dy 3 , 15 Cu 4 Dy, 16 Cu 4 Dy 4 , 17 Cu 4 Dy 12 , 13 Cu 5 Dy 2 , 18 Cu 5 Dy 4 , 19 Cu 6 Dy 2 , 20 Cu 6 Dy 3 , 21 Cu 6 Dy 6 , 22 Cu 8 Dy 2 , 23 Cu 8 Dy 3 , 24 Cu 8 Dy 4 , 25 Cu 8 Dy 9 , 26 Cu 12 Dy 8 , 27 Cu 22 Dy 6 , 28 Cu 24 Dy 8 , 29 and Cu 36 Dy 24 . 30 However, the ligand design rationale to fine tune the cluster nuclearity is yet to get a general shape, and therefore, it is still an object of intensive research.…”

Crystal structure of methyl 1,3-benzoxazole-2-carboxylate

“…A search of the Cambridge Structural Database (CSD, version of November 2020; Groom et al, 2016) found only twelve benzoxazoles substituted by a carbonyl group on the 2-position. In almost half of the cases, the benzoxazole derivative is used as a ligand to complex an Ni, Co or Cu atom (CAYSIG and CAYSOM;Iasco et al, 2012;LAJNAN;Zhang et al, 2010), or incorporated in a macromolecule (NESPUY; Lim et al, 2012;LUYJUL;Osowska & Miljanic ´, 2010), resulting in a geometry quite far from that of a small entity. Among the remaining examples, the benzoxazolylcarbonyl moiety may be linked to an aromatic group.…”