Synthesis and1H NMR studies of paramagnetic nickel(ii) complexes containing bis(pyrazolyl)methane ligands with dendritic substituents

Zinc-Catalyzed Hydroboration of Carbon Dioxide Amplified by Borane-Tethered Heteroscorpionate Bis(Pyrazolyl)methane Ligands

The borane-functionalized (BR2) bis(3,5-dimethylpyrazolyl)methane (LH) ligands 1a (BR2: 9-borabicyclo[3.3.1]nonane or 9-BBN), 1b (BR2: BCy2), and 1c (BR2: B(C6F5)2) were synthesized by the allylation-hydroboration of LH. Metalation of 1a,b with ZnCl2 yielded the heteroscorpionate dichloride complexes [(1a,b)ZnCl2] 3a,b. The reaction of 1a with ZnEt2 led to the formation of the zwitterionic complex [Et(1a)ZnEt(THF)] 5. The reaction of complex 3a with two equivalents of KHBEt3 under a carbon dioxide (CO2) atmosphere gave rise to the formation of the dimeric bis(formate) complex [(1a)Zn(OCHO)2]2 8, in which its borane moieties intermolecularly stabilize the formate ligands of opposite metal centers. The allylated precursor Lallyl and its zinc dichloride, diethyl and bis(formate) complexes [(Lallyl)ZnCl2] 2, [(Lallyl)ZnEt2] 4, and [(Lallyl)Zn(OCHO)2] 7 were also isolated. The catalyst systems composed of 1 mol % of 3a or 3b and two equivalents of KHBEt3 hydroborated CO2 at 1 bar with pinacolborane (HBPin) to the methanol-level product H3COBPin (and PinBOBPin) in yields of 42 or 86%, respectively. The catalyst systems using the unfunctionalized complex [(LH)ZnCl2] 6 and KHBEt3 or KHBEt3/nOctBR2 (BR2: 9-BBN or BCy2) hydroborated CO2 to H3COBPin but in 2.5- to 6-fold lower activities than those exhibited by 3a,b/KHBEt3. The hydroboration of CO2 using 8 as a catalyst led to yields of 39-43%, comparable to those obtained with 3a/KHBEt3. The results confirmed that the catalytic intermediates benefit from the incorporated boranes' intra- or intermolecular stabilizations.

Metal-free, Mild, and Selective Synthesis of Bis(pyrazolyl)alkanes by Nucleophile-Catalyzed Condensation

Bis(pyrazolyl)alkanes are a prolific class of ligands for catalysis, accessible by the condensation between bis(pyrazolyl)methanones and carbonyls. In this report, we describe a nucleophile-catalyzed innovation on this condensation that avoids the transition metals, high temperatures, reagent excess, and air-sensitive reagents common among the existing protocols. Significantly, this method accommodates sterically hindered and electronically diverse pyrazoles and aldehydes, applicable for systematic ligand optimization. Furthermore, our scope includes azoles and bridging functional groups previously unreported for this reaction, promising for new heteroscorpionate catalysts. We provide the first direct evidence for an elusive reaction intermediate and characterize the most complete mechanism for this condensation.

A pyrazolopyrimidine based fluorescent probe for the detection of Cu2+ and Ni2+ and its application in living cells

A fluorescent sensor L based on a pyrazolopyrimidine core simultaneously detects Cu²⁺ and Ni²⁺ ions by photoluminescence quenching, even in the presence of other metal cations. Sensor L possesses high association constants of 5.24 × 10³ M^-1 and 2.85 × 10⁴ M^-1 and low detection limits of 0.043 μM and 0.038 μM for Cu²⁺ and Ni²⁺, respectively. The binding stoichiometry ratios of L to Cu²⁺ or Ni²⁺ is 1:1 as determined by Benesi-Hildebrand and Job's plots, and by crystal structures. DFT calculations on L-Cu²⁺ indicated reduced electron donation from the coordinated pyrazolopyridine to the fused pyrimidine and pendant phenyl group which, together with a smaller HOMO-LUMO orbital gap could favour non-radiative decay and explain the observed fluorescence quenching. Sensor L possessed low cytotoxicity and good imaging characteristics for Cu²⁺ and Ni²⁺ in living cells, suggesting potential applications for detecting Cu²⁺ and Ni²⁺in vivo.

Homogeneous photochemical water oxidation with metal salophen complexes in neutral media

The development of water oxidation catalysts based on Earth-abundant metals that can function at neutral pH remains a basic chemical challenge.

Propentdyopent: the scaffold of a heme metabolite as an electron reservoir in transition metal complexes

The dipyrrin-1,9-dione scaffold of heme metabolite propendyopent coordinates late transition metals (Co, Ni, Cu, and Zn) forming homoleptic, pseudo-tetrahedral complexes. Electrochemical and spectroscopic studies reveal that the monoanionic, bidentate ligands behave as electron reservoirs as the complexes reversibly host one or two ligand-based radicals.