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Synthesis of (Arylmido)niobium(V) Complexes Containing Ketimide, Phenoxide Ligands, and Some Reactions with Phenols and Alcohols.

ABSTRACT: Reactions of Nb(NAr)(N=C ^t Bu₂)₃ (3a, Ar = 2,6-Me₂C₆H₃) with 1.0, 2.0, or 3.0 equiv of Ar'OH (Ar' = 2,6- ⁱ Pr₂C₆H₃) afforded Nb(NAr)(N=C ^t Bu₂)₂(OAr'), Nb(NAr)(N=C ^t Bu₂)(OAr')₂, or Nb(NAr)(OAr')₃, respectively (at 25 °C), whereas the reaction with 2.0 equiv of 2,6- ^t Bu₂C₆H₃OH afforded Nb(NAr)(N=C ^t Bu₂)₂(O-2,6- ^t Bu₂C₆H₃) upon heating (70 °C) without the formation of bis(phenoxide) and the reaction of 3a with 2.0 equiv of 2,4,6-Me₃C₆H₂OH afforded Nb(NAr)(N=C ^t Bu₂)(O-2,4,6-Me₃C₆H₂)₂(HN=C ^t Bu₂). Similar reactions of 3a with 1.0 equiv of (CF₃)₃COH or 2.0 equiv of (CF₃)₂CHOH afforded Nb(NAr)(N=C ^t Bu₂)₂[OC(CF₃)₃](HN=C ^t Bu₂) or Nb(NAr)(N=C ^t Bu₂)[OCH(CF₃)₂]₂(HN=C ^t Bu₂), respectively. On the basis of their structural analyses and the reaction chemistry, it was suggested that these reactions proceeded via coordination of phenol (alcohol) to Nb and the subsequent proton (hydrogen) transfer to the ketimide (N=C ^t Bu₂) ligand. The reaction of Nb(NAr)(N=C ^t Bu₂)₂(OAr') with 1.0 equiv of 2,4,6-Me₃C₆H₂OH gave the disproportionation products Nb(NAr)(N=C ^t Bu₂)(OAr')₂ and Nb(NAr)(N=C ^t Bu₂)(O-2,4,6-Me₃C₆H₂)₂(HN=C ^t Bu₂) with 1:1 ratio, clearly indicating the presence of the above mechanism and the fast equilibrium (between the ketimide and the phenoxide). The reaction of 3a with 1.0 or 2.0 equiv of C₆F₅OH afforded Nb(N=C ^t Bu₂)₂(OC₆F₅)₃(HN=C ^t Bu₂) as the sole isolated product, which was formed from once generated Nb(NAr)(N=C ^t Bu₂)₂(OC₆F₅)(HN=C ^t Bu₂) by treating with C₆F₅OH.

SUBMITTER: Srisupap N

PROVIDER: S-EPMC6644436 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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Synthesis of (Arylmido)niobium(V) Complexes Containing Ketimide, Phenoxide Ligands, and Some Reactions with Phenols and Alcohols.

Srisupap Natta N Wised Kritdikul K Tsutsumi Ken K Nomura Kotohiro K

ACS omega 20180607 6

Reactions of Nb(NAr)(N=C t Bu2)3 (3a, Ar = 2,6-Me2C6H3) with 1.0, 2.0, or 3.0 equiv of Ar'OH (Ar' = 2,6- i Pr2C6H3) afforded Nb(NAr)(N=C t Bu2)2(OAr'), Nb(NAr)(N=C t Bu2)(OAr')2, or Nb(NAr)(OAr')3, respectively (at 25 °C), whereas the reaction with 2.0 equiv of 2,6- t</ ...[more]

PMID: 31458800

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Project description:Novel lanthanide (Ln) compounds [Ln(L)2]Cl.xH2O (Ln = La3+, Ce3+, Sm3+) containing aromatic N,O-chelate ligands [HL1 = 4-amino-2-(1H-benzimidazol-2-yl)phenol; HL2 = 5-amino-2-(1H-benzimidazol-2-yl)phenol] have been synthesized and structurally characterized by elemental analysis, NMR and IR spectroscopy, molar conductance measurements, and mass spectrometry (MS). The spectroscopic data suggested that the benzimidazolyl-phenol ligands act as N,O-chelate ligands through the iminic nitrogen and phenolic oxygen atoms. Elemental analysis indicated that lanthanide compounds were formed in a 1:2 stoichiometry (metal:ligand). In vitro biological evaluation was carried out using these complexes, exhibiting moderate cytotoxicity against six different human tumor cell lines (U251, human glioblastoma; HCT-15, colorectal carcinoma; MCF-7, breast epithelial adenocarcinoma; PC-3, prostate cancer; K562, myelogenous leukemia; SKLU-1, lung carcinoma) and lower toxicity against a non-cancerous cell line (COS-7, primate kidney). In addition, the antibacterial activity of the compounds was assessed against two gram-positive strains (Staphylococcus aureus ATCC 25923, Listeria monocytogenes ATCC 19115) and two gram-negative strains (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27583) using the microdilution method. The results obtained show that the metal complexes exhibit higher biological activity than the free ligands, confirming a synergistic effect. Further benzimidazolyl-phenol derivatives were explored for the detection of bacteria using fluorescence imaging studies. Interestingly, the fluorescent properties of these compounds make them potential candidates to monitor the morphology of bacteria at different compound concentrations. Hence, the interaction of the ligand and complexes with model membranes mimicking those of bacteria was studied by using differential scanning calorimetry (DSC) and molecular dynamics (MD), showing that both compounds decreased the enthalpy of transition in two model membranes as the concentration of the compounds increased. In addition, the main transition temperature was slightly reduced as a result of these interactions.

Dataset Information

Synthesis of (Arylmido)niobium(V) Complexes Containing Ketimide, Phenoxide Ligands, and Some Reactions with Phenols and Alcohols.

Publications

Synthesis of (Arylmido)niobium(V) Complexes Containing Ketimide, Phenoxide Ligands, and Some Reactions with Phenols and Alcohols.

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