Fluorenyl-tethered N-heterocyclic carbene (NHC): an exclusive C-donor ligand for heteroleptic calcium and strontium chemistry

Exclusive C-donating ligands are rarely used with kinetically labile heavier alkaline earths (Ca, Sr, Ba). We report herein the aptitude of a combination of NHC with fluorenyl connected by a flexible -(CH2)2- linker as a ligand support for heteroleptic Ca- and Sr-N(SiMe3)2 and iodides. The Ca-N(SiMe3)2 complex even catalyzes the intramolecular hydroamination of aminoalkenes to showcase the effectiveness of this ligand framework.

Synthesis, Structure, and Reactivity of Magnesium Pentalenides

The first magnesium pentalenide complexes have been synthesized via deprotonative metalation of 1,3,4,6-tetraphenyldihydropentalene (Ph4PnH2) with magnesium alkyls. Both the nature of the metalating agent and the reaction solvent influenced the structure of the resulting complexes, and an equilibrium between Mg[Ph4Pn] and [nBuMg]2[Ph4Pn] was found to exist and investigated by NMR, XRD, and UV-vis spectroscopic techniques. Studies on the reactivity of Mg[Ph4Pn] with water, methyl iodide, and trimethylsilylchloride revealed that the [Ph4Pn]2- unit undergoes electrophilic addition at 1,5-positions instead of 1,4-positions known for the unsubstituted pentalenide, Pn2-, highlighting the electronic influence of the four aryl substituents on the pentalenide core. The ratio of syn/anti addition was found to be dependent on the size of the incoming electrophile, with methylation yielding a 60:40 mixture, while silylation yielded exclusively the anti-isomer.

Formation and Reactivity of a Hexahydridosilicate [SiH6]2- Coordinated by a Macrocycle-Supported Strontium Cation

The cationic benzyl complex [(Me₄TACD)Sr(CH₂Ph)][A] (Me₄TACD=1,4,7,10‐tetramethyltetraazacyclododecane; A=B(C₆H₃‐3,5‐Me₂)₄) reacted with two equivalents of phenylsilane to give the bridging hexahydridosilicate complex [(Me₄TACD)₂Sr₂(thf)₄(μ‐κ³ : κ³‐SiH₆)][A]₂ (3 a). Rapid phenyl exchange between phenylsilane molecules is assumed to generate monosilane SiH₄ that is trapped by two strontium hydride cations [(Me₄TACD)SrH(thf)_x]⁺. Complex 3 a decomposed in THF at room temperature to give the terminal silanide complex [(Me₄TACD)Sr(SiH₃)(thf)₂][A], with release of H₂. Upon reaction with a weak Brønsted acid, CO₂, and 1,3,5,7‐cyclooctatetraene SiH₄ was released. The reaction of a 1 : 2 mixture of cationic benzyl and neutral dibenzyl complex with phenylsilane gave the trinuclear silanide complex [(Me₄TACD)₃Sr₃(μ₂‐H)₃(μ₃‐SiH₃)₂][A], while ⁿOctSiH₃ led to the trinuclear (n‐octyl)pentahydridosilicate complex [(Me₄TACD)₃Sr₃(μ₂‐H)₃(μ₃‐SiH₅ⁿOct)][A].

Synthesis, antimicrobial, anti-cancer and in silico studies of new urea derivatives

The reaction of an alkyl or aryl isocyanates with some primary amines in acetonitrile at room temperature afforded the corresponding alkyl- and aryl-urea derivatives. All the prepared urea compounds have been elucidated by FTIR, NMR, and elemental analysis. The compounds 1 and 3 were confirmed by single-crystal X-ray diffraction. The 4-tolylsulfonyl isocyanate reacted with the aryl amines 1, 2, 3, and 2,4-dichloroaniline to afford the corresponding sulfonylurea derivatives 5-8. Likewise, the reaction of the isocyanates with 2,4-dichloroaniline, 5-methyl isoxazole-3-amine, and 2-aminothiazole derivatives gave the corresponding urea derivatives 9-17. All the prepared compounds 5-17 were tested in vitro as anti-microbial and anti-HepG2 agents. Moreover, analyzing gene expression of TP53-exon4 and TP53-exon7, DNA damage values, and DNA fragmentation percentages have been discussed. The compounds 5 and 8 recorded the highest activity against the tested microbial strains with maximum activity against C. albicans (50 mm) and B. mycoides (40 mm), respectively. The compounds 5 inhibited the growth of E. coli, S. aureus, and C. Albicans at the MIC level of 0.0489 µM, while the compound 8 was able to inhibit the visible growth of E. coli and C. albicans at MIC value of 3.13 µM and S. aureus at 0.3912 µM. In the same line, compound 5 showed the best cytotoxic activity against the HepG2 cell line (IC₅₀ = 4.25 µM) compared to 5 fluorouracil with IC₅₀ = 316.25 µM. Expression analysis of liver cancer related to a gene including TP53-exon4 and TP53-exon7 was used in HepG2 Liver cancer cell lines using RT-qPCR. The expression values of TP53-exon4 and TP53-exon7 genes were decreased. The DNA damage values and DNA fragmentation percentages were increased significantly (P < 0.01) in the treated HepG2 (5) sample compared with the negative control. Docking studies were performed for the synthetic compounds against 2 bacterial proteins (DNA gyrase subunit B, and penicillin binding protein 1a) that are known targets for some antibiotics, and one cell division protein kinase 2 (CDK2) as target for anticancer drugs.

Reduction of 1,3,5,7-cyclooctatetraene by a molecular calcium hydride: an even electron polarised insertion/deprotonation mechanism

The reductive aromatisation of 1,3,5,7-cyclooctatetraene by a dimeric calcium hydride occurs via two electron steps and does not necessitate the formation of radical intermediates.

Reduction vs. Addition: The Reaction of an Aluminyl Anion with 1,3,5,7-Cyclooctatetraene

The potassium aluminyl complex K[Al(NON^Ar )] (NON=NON^Ar =[O(SiMe₂ NAr)₂ ]^2- , Ar=2,6-iPr₂ C₆ H₃ ) reacts with 1,3,5,7-cyclooctatetraene (COT) to give K[Al(NON^Ar )(COT)]. The COT-ligand is present in the asymmetric unit as a planar μ₂ -η² :η⁸ -bridge between Al and K, with additional K⋅⋅⋅π-aryl interactions to neighboring molecules that generate a helical chain. DFT calculations indicate significant aromatic character, consistent with reduction to [COT]^2- . Addition of 18-crown-6 causes a rearrangement of the C₈ -carbocycle to form the isomeric 9-aluminabicyclo[4.2.1]nona-2,4,7-triene anion.