In situ tracking and characterisation of scorpionate ligands via11B-NMR spectroscopy

Using 11B-NMR spectroscopy for the in situ tracking and characterisation of the well known scorpionate ligand class. Five examples are included.

Synthesis, Characterization and Assessment of the Antioxidant Activity of Cu(II), Zn(II) and Cd(II) Complexes Derived from Scorpionate Ligands

Seeking to enrich the yet less explored field of scorpionate complexes bearing antioxidant properties, we, here, report on the synthesis, characterization and assessment of the antioxidant activity of new complexes derived from three scorpionate ligands. The interaction between the scorpionate ligands thallium(I) hydrotris(5-methyl-indazolyl)borate (TlTp4Bo,5Me), thallium(I) hydrotris(4,5-dihydro-2H-benzo[g]indazolyl)borate (TlTpa) and potassium hydrotris(3-tert-butyl- pyrazolyl)borate (KTptBu), and metal(II) chlorides, in dichloromethane at room temperature, produced a new family of complexes having the stoichiometric formula [M(Tp4Bo,5Me)2] (M = Cu, 1; Zn, 4; Cd, 7), [M(Tpa)2] (M = Cu, 2; Zn, 5; Cd, 8), [Cu(HpztBu)3Cl2] (3), [Zn(TptBu)Cl] (6) and [Cd(BptBu)(HpztBu)Cl] (9). The obtained metal complexes were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance and elemental analysis, highlighting the total and partial hydrolysis of the scorpionate ligand TptBu during the synthesis of the Cu(II) complex 3 and the Cd(II) complex 9, respectively. An assessment of the antioxidant activity of the obtained metal complexes was performed through both enzymatic and non-enzymatic assays against 1,1-diphenyl-2-picryl- hydrazyl (DPPH·), 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+·), hydroxyl (HO·), nitric oxide (NO·), superoxide (O2−) and peroxide (OOH·) radicals. In particular, the complex [Cu(Tpa)2]⋅0.5H2O (2) exhibited significant antioxidant activity, as good and specific activity against superoxide (O2−·), (IC50 values equal to 5.6 ± 0.2 μM) and might be identified as auspicious SOD-mimics (SOD = superoxide dismutase).

Novel Chemotherapeutic Agents - The Contribution of Scorpionates

: The development of safe and effective chemotherapeutic agents is one of the uppermost priorities and challenges of medicinal chemistry and new transition metal complexes are being continuously designed and tested as anticancer agents. Scorpionate ligands have played a great role in coordination chemistry, since their discovery by Trofimenko in the late 1960s, with significant contributions in the fields of catalysis and bioinorganic chemistry. Scorpionate metal complexes have also shown interesting anticancer properties, and herein, the most recent (last decade) and relevant scorpionate complexes reported for application in medicinal chemistry as chemotherapeutic agents are reviewed. The current progress on the anticancer properties of transition metal complexes bearing homo- or hetero- scorpionate ligands, derived from bis- or tris-(pyrazol-1-yl)-borate or -methane moieties is highlighted.

Relative hemilabilities of H2B(az)2 (az = pyrazolyl, dimethylpyrazolyl, methimazolyl) chelates in the complexes [M(η-C3H5)(CO)2{H2B(az)2}] (M = Mo, W)

The question of B–H–Mo hemilability in a range of dihydrobis(azolyl)borate scorpionate ligands is discussed with reference to η3-allyl complexes [Mo(η3-C3H5)(CO)2{H2B(az)2}] [az = pyrazolyl (pz), dimethylpyrazolyl (pz*), mercaptoimidazolyl (mt)].

Mono- and Hexanuclear Zinc Halide Complexes with Soft Thiopyridazine Based Scorpionate Ligands

Scorpionate ligands with three soft sulfur donor sites have become very important in coordination chemistry. Despite its ability to form highly electrophilic species, electron-deficient thiopyridazines have rarely been used, whereas the chemistry of electron-rich thioheterocycles has been explored rather intensively. Here, the unusual chemical behavior of a thiopyridazine (6-tert-butylpyridazine-3-thione, HtBuPn) based scorpionate ligand towards zinc is reported. Thus, the reaction of zinc halides with tris(6-tert-butyl-3-thiopyridazinyl)borate Na[TntBu] leads to the formation of discrete torus-shaped hexameric zinc complexes [TntBuZnX]6 (X = Br, I) with uncommonly long zinc halide bonds. In contrast, reaction of the sterically more demanding ligand K[TnMe,tBu] leads to decomposition, forming Zn(HPnMe,tBu)2X2 (X = Br, I). The latter can be prepared independently by reaction of the respective zinc halides and two equiv of HPnMe,tBu. The bromide compound was used as precursor which further reacts with K[TnMe,tBu] forming the mononuclear complex [TnMe,tBu]ZnBr(HPnMe,tBu). The molecular structures of all compounds were elucidated by single-crystal X-ray diffraction analysis. Characterization in solution was performed by means of 1H, 13C and DOSY NMR spectroscopy which revealed the hexameric constitution of [TntBuZnBr]6 to be predominant. In contrast, [TnMe,tBu]ZnBr(HPnMe,tBu) was found to be dynamic in solution.

Iron(ii) tetrafluoroborate complexes of new tetradentate C-scorpionates as catalysts for the oxidative cleavage of trans-stilbene with H2O2

Iron(ii) complexes of two new tetradentate C-scorpionate ligands are characterized. Both catalyze stilbene cleavage using either H2O2 or a O2/photocatalyst oxidant.

Heteroleptic cobalt(iii) acetylacetonato complexes with N-heterocyclic carbine-donating scorpionate ligands: synthesis, structural characterization and catalysis

A first structure-determined heteroleptic cobalt(iii) complex with the less hindered tris(carbene)borate works as a catalyst precursor for alkane oxidation.