Isostructural Potassium and Thallium Salts of Sterically Crowded Triazenes: A Structural and Computational Study

Thallium(I) Complexes of Tris(pyridyl)borates and a Comparison to Their Pyrazolyl Analogues

Thallium(I) complexes of B-methylated and B-phenylated tris(pyridyl)borates featuring trifluoromethyl groups at the pyridyl ring 6-positions have been synthesized by metathesis using the corresponding potassium salts [MeB(6-(CF3)Py)3]K and [PhB(6-(CF3)Py)3]K with thallium(I) acetate. The closely related tris(pyrazolyl)borate analogue [PhB(3-(CF3)Pz)3]Tl has also been prepared, and comparisons of structural and spectroscopic features between the two scorpionate families are presented. [MeB(6-(CF3)Py)3]Tl displays κ3-coordination of the tris(pyridyl)borate similar to that of tris(pyrazolyl)borate in [MeB(3-(CF3)Pz)3]Tl, while [PhB(6-(CF3)Py)3]Tl and [PhB(3-(CF3)Pz)3]Tl feature κ2-N,N ligand coordination modes with the B-phenyl groups flanking the thallium sites. 19F NMR spectroscopy of [MeB(6-(CF3)Py)3]Tl reveals the presence of a remarkably large 1208 Hz four-bond thallium-fluorine coupling constant in chloroform at room temperature, which is considerably larger than 878 Hz observed for the pyrazolyl borate analogue [MeB(3-(CF3)Pz)3]Tl. Although [PhB(6-(CF3)Py)3]Tl is structurally nonrigid at room temperature in chloroform, at lower temperatures, the ligand arm exchange slows down, revealing 4JTl-F = 1110 Hz. Steric demands of these ligands have been quantified using the buried volume concept. In addition, ligand transfer chemistry from [MeB(6-(CF3)Py)3]Tl and [PhB(6-(CF3)Py)3]Tl to copper(I) under ethylene and computational analyses of the various coordination modes of tris(pyrazolyl)borates and tris(pyridyl)borates are reported.

Group 13 Heavier Carbene Analogues Stabilized by the Bulky Bis(4-benzhydryl-benzoxazol-2-yl)methanide Ligand

On the basis of the bulky bis(4-benzhydryl-benzoxazyl-2-yl)methane ligand (^4-BzhH2Box₂CH₂), neutral monovalent group 13 complexes [M₁₃(^4-BzhH2Box₂CH)] [M₁₃ = Tl (1), In (2), or Ga (3)] have been synthesized by salt metathesis reaction of the corresponding potassium or sodium precursor and TlOTf, InOTf, or "GaI". The diiodido gallium species [GaI₂(^4-BzhH2Box₂CH)] (3a) was realized as a byproduct once the synthesis of 3 was carried out at higher temperatures. The synthesis of [AlI₂(^4-BzhH2Box₂CH)] (6) as a potential precursor for an aluminum(I) congener was accomplished by two alternative synthetic routes. During one of those procedures, [AlMe₂(^4-BzhH2Box₂CH)] (4) was synthesized in good yields by deprotonation with an AlMe₃ solution (method A). Subsequently, 4 was converted to the monoiodinated species [AlMeI(^4-BzhH2Box₂CH₂)] (5) using 1 equiv of I₂ or to 6 by iodination with 2 equiv of I₂ at 70 °C for 4 days. As an alternative, complex 6 could be prepared by iodination of 1 equiv of I₂ and [AlH₂(^4-BzhH2Box₂CH)] (7), which was previously obtained by facile reaction of ^4-BzhH2Box₂CH₂ and AlH₃NMe₂Et. All main products 1-7 were completely characterized by nuclear magnetic resonance spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray structure determination. Alane 7 was additionally analyzed by solid-state fluorescence spectroscopy. Density functional theory calculations on [M₁₃(^4-BzhH2Box₂CH)] [M₁₃ = Tl (1), In (2), Ga (3), or Al] revealed that the complexes consist of monovalent group 13 cations coordinated by an anionic (^4-BzhH2Box₂CH) ligand similar to metallacycles incorporating a NacNac ligand.

A Tale of Biphenyl and Terphenyl Substituents for Structurally Diverse Ketiminato Magnesium, Calcium and Germanium Complexes

In this paper, we have used two N,O-ketiminato ligands (L1 and L2) with biphenyl and terphenyl substituent on the nitrogen atom. Deprotonation of L1 with KN(SiMe₃ )₂ and subsequent reaction with MgI₂ led to a homoleptic dinuclear magnesium complex (1) with a Mg₂ O₂ four-membered ring. Deprotonation with nBuLi and subsequent reaction with MgI₂ afforded a unusual dinuclear magnesium complex (2) with a Mg₂ O₂ ring. Extension of the ligand for calcium resulted in a trinuclear calcium complex (3) with six four-membered Ca₂ O₂ rings. We could not isolate any chelating complex when L2 was used as a ligand, and only oxygen bound magnesium (4) and calcium (5) adducts were isolated. DFT studies were performed to understand this dissimilar behavior. More diverse results were obtained when lithiated L1 and L2 were treated with germanium dichloride. We were able to stabilize a monomeric germylene monochloride (7) with L1. However, with L2, an unusual ligand scrambling, and a C-C coupling take place, leading to the formation of a secondary carbocation with GeCl₃ - as a counter-anion (8). Besides, a germanium dichloride adduct (9) bound to the oxygen center of the ligand was obtained as the minor product.

Bulky bis(aryl)triazenides: just aspiring amidinates? A structural and spectroscopic study

The triazenide ligand is compared to the isoelectronic formamidinate with regards donor capacity, coordination chemistry and capacity to stabilise reactive main group species.

Synthetic, Structural, and Computational Studies on Heavier Tetragen and Chalcogen Triazenide Complexes

The syntheses of the triazenide complexes [{N(N^Dipp)₂}₂M] (Dipp = 2,6-di-isopropylphenyl; M = Ge(II) (1), Sn(II) (2), Pb(II) (3), and Te(II) (5)) are described for the first time. These compounds have been characterized by single-crystal X-ray diffraction and heteronuclear NMR spectroscopy. Density functional theory calculations were employed to confirm the presence and nature of the stereochemically active lone pairs in 1-5, alongside the Gibbs energy changes for their general synthesis, which enable the rationalization of observed reactivities.

Kinetic stabilization of low-oxidation state and terminal hydrido main group metal complexes by a sterically demanding N,N′-bis(2,6-terphenyl)triazenide

Thermally robust main group metal complexes featuring terminal hydride ligands are achieved by deploying a sterically demanding N,N′-bis(2,6-terphenyl)triazenide ligand.

Structural diversity in a homologous series of donor free alkali metal complexes bearing a sterically demanding triazenide

The isolation and structural characterization of donor free alkali metal complexes of a bis(terphenyl) substituted triazenide are presented.

Synthesis of a Molecule with Four Different Adjacent Pnictogens

The synthesis of a molecule containing four adjacent different pnictogens was attempted by conversion of a Group 15 allyl analogue anion [Mes*NAsPMes*](-) (Mes*=2,4,6-tri-tert-butylphenyl) with antimony(III) chloride. A suitable precursor is Mes*N(H)AsPMes* (1) for which several syntheses were investigated. The anions afforded by deprotonation of Mes*N(H)AsPMes* were found to be labile and, therefore, salts could not be isolated. However, the in situ generated anions could be quenched with SbCl3 , yielding Mes*N(SbCl2 )AsPMes* (4).

Regulation of the p53 response and its relationship to cancer

p53 has been studied intensively as a major tumour suppressor that detects oncogenic events in cancer cells and eliminates them through senescence (a permanent non-proliferative state) or apoptosis. Consistent with this role, p53 activity is compromised in a high proportion of all cancer types, either through mutation of the TP53 gene (encoding p53) or changes in the status of p53 modulators. p53 has additional roles, which may overlap with its tumour-suppressive capacity, in processes including the DNA damage response, metabolism, aging, stem cell differentiation and fertility. Moreover, many mutant p53 proteins, termed 'gain-of-function' (GOF), acquire new activities that help drive cancer aggression. p53 is regulated mainly through protein turnover and operates within a negative-feedback loop with its transcriptional target, MDM2 (murine double minute 2), an E3 ubiquitin ligase which mediates the ubiquitylation and proteasomal degradation of p53. Induction of p53 is achieved largely through uncoupling the p53-MDM2 interaction, leading to elevated p53 levels. Various stress stimuli acting on p53 (such as hyperproliferation and DNA damage) use different, but overlapping, mechanisms to achieve this. Additionally, p53 activity is regulated through critical context-specific or fine-tuning events, mediated primarily through post-translational mechanisms, particularly multi-site phosphorylation and acetylation. In the present review, I broadly examine these events, highlighting their regulatory contributions, their ability to integrate signals from cellular events towards providing most appropriate response to stress conditions and their importance for tumour suppression. These are fascinating aspects of molecular oncology that hold the key to understanding the molecular pathology of cancer and the routes by which it may be tackled therapeutically.

1,3-Bis(2,4,6-trimethylphenyl)triazenides of potassium, magnesium, calcium, and strontium

1,3-Bis(2,4,6-trimethylphenyl)triazenide anions act as bidentate ligands toward s-block metals; in the calcium derivative π-stacking of the aromatic rings leads to additional stabilization of the complex.

Accessing heavy allyl-analogous [(TerN)2E]− (E = Sb, Bi) ions and their reactivity towards ECl3

Highly reactive heavy heteroatom allyl analogues were obtained by reduction of 1,3-dichloro-cyclo-1,3-dipnicta-2,4-diazanes.

Noncovalent interactions of metal cations and arenes probed with thallium(I) complexes

The synthesis, characterization, and computational analysis of Tl(I) complexes bearing the bis(imino)pyridine scaffold, [{ArN═CPh}2(NC5H3)]Tl(+)(OTf)(-) (Ar = 2,6-Et2C6H33, 2,5-(t)Bu2C6H3, 4), are reported. The cations of these species showed long Tl-N and Tl-OTf distances indicating only weak or no ligand coordination. Computational analysis of the interactions between the Tl cation and the ligands (orbital populations, bond order, and energy decomposition analysis) point to only minimal covalent interactions of the cation with the ligands. The weak ligand-to-metal donation allows for additional interactions between the Tl cation and arene rings that are either intramolecular, in the case of 3, or intermolecular. From benzene or toluene, 4 crystallizes with inverted sandwich structures having two [{(2,5-(t)Bu2C6H3)N═CPh}2(NC5H3)]Tl(+) cations bridged by either benzene or toluene. A density functional computational description of these Tl-arene contacts required exchange-correlation functionals with long-range exchange corrections (e.g., CAM-B3LYP or LC-PBE) and show that Tl-arene contacts are stabilized by noncovalent interactions.