Heteroscorpionate-Based Co²⁺, Zn²⁺, and Cu²⁺ Complexes: Coordination Behavior, Aerobic Oxidation, and Hydrogen Sulfide Detection

Abstract

The coordination behavior and reactivity of the phenol-substituted bis(pyrazolyl)methane ligands, (3,5-(t)Bu(2)-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L1-H) and 2-phenol-bis(3,5-Me(2)-pyrazol-1-yl)methane (L2-H) have been investigated in the metal complexes (L1-H)CoCl(2) (1), (L1-H)ZnCl(2) (2), (L3)CuCl(2) (3), (L2)(2)Co(2)Cl(2) (4) (L2-H)ZnCl(2) (5), and (L2-H)CuCl(2)·H(2)O (6). The mononuclear tetrahedral cobalt complex 1 was isolated and fully characterized by X-ray single crystal diffraction and (1)H NMR spectroscopy and relaxometry. The neutral L1-H is κ(2)-coordinated to the metal center whereas the not coordinated hydroxy-phenyl group is involved in extended intermolecular hydrogen bonds. Aerobic oxidation of L1-H was observed in the reaction of this ligand with CuCl(2) to yield the para-quinone derivative L3 (L3 = 2-(t)Bu-6-(bis(3,5-Me(2)-pyrazol-1-yl)methyl)cyclohexa-2,5-diene-1,4-dione). Upon oxidation L3 resulted κ(2)-coordinated to the tetrahedral Cu(II) metal center, affording 3. The reaction of L2-H with CoCl(2)·6H(2)O produced the elimination of 1 equiv of hydrochloric acid and the formation of the binuclear complex 4 in which one cobalt is in an octahedral environment featuring two κ(3)-coordinated deprotonated ligands whereas the second cobalt center is detected in tetrahedral coordination geometry, bound to the octahedral cobalt via two phenoxo bridging moieties. Interestingly L2-H, (3-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L4-H), or (5-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L5-H) were not oxidized in the reaction with CuCl(2). The reaction of the ligand L2-H with ZnCl(2) and CuCl(2)·2H(2)O yielded the κ(2)-coordinated tetrahedral complex 5 and the square planar complex 6, respectively. The application of the cobalt complex 1 as molecular dosimeter for H(2)S was explored and compared to that of the zinc analogue 2. Density functional theory (DFT) calculations and NMR experiments to assess the possible mechanisms of H(2)S detection by both 1 and 2 are also described.

A Copper Porphyrin for Sensing H2S in Aqueous Solution via a “Coordinative‐Based” Approach

“…generally produce fluorescence turn-on changes via H 2 Smediated precipitation of Mt-S. [1,[32][33][34][39][40][41][42] Despite all the advantages of the above mentioned probes (e.g. high selectivity and sensitivity), some shortcomings typically involve slow response and poor water solubility.…”

A Cyclam‐Based Fluorescent Ligand as a Molecular Beacon for Cu2+ and H2S Detection

“…[39][40][41][42][43][44][45][46][47] Our studies on the implementation of devices for monitoring H 2 S started some time ago and focused both on properly tailored low-molecular-mass compounds and on natural metalloproteins. [48][49][50][51][52][53][54][55][56][57][58][59][60] Drawing upon these considerations, we designed a cyclambased fluorescent molecule (see py-cyclam-pyr in Scheme 1) to evaluate its ability in the recognition of Cu 2+ . The chelating unit py-cyclam is a cross-bridged cyclam derivative with a pyridyl donor atom integrated into the cross-bridge, which results in a pentadentate ligand.…”

“…Thus, implementation of H 2 S fluorescence‐based probes is still considered a very challenging task, and it has attracted much attention from several research groups in the world . Our studies on the implementation of devices for monitoring H 2 S started some time ago and focused both on properly tailored low‐molecular‐mass compounds and on natural metalloproteins …”

Synthesis of Bis(benzotriazol-1-yl)methane Derivatives by Cobalt-Catalyzed Formation of C-C Bonds

“…A reaction mechanism was subsequently proposed [2,3], indicating the crucial role of the coordination of the metal centre to the free nitrogen atoms for the activation of the N-C(O) bonds in the bis(pyrazol-1-yl)methanone skeleton. The synthetic approach was then extended by other research groups to functionalized aldehydes [4][5][6][7][8], with the aim of preparing pyrazole-based ligands to be applied in coordination [9][10][11][12][13][14][15][16][17], bioinorganic [18][19][20][21], organometallic chemistry and homogeneous catalysis [22][23][24][25][26][27][28].…”