Dicationic Tellurium Analogues of the Classic N‐Heterocyclic Carbene

Structural verification and new reactivity for Stang's reagent, [PhI(CN)][OTf]

The structure of Stang's reagent [PhI(CN)][OTf] is confirmed by X-ray crystallography and is determined to be best described as an ion-pair in organic solution. It is found to be a strong Lewis acid, but reaction with pyridine ligands gives [Pyr-CN][OTf] salts via oxidation of pyridine giving a new derivative of the CDAP reagent widely used as an activation agent for polysaccharides.

Synthesis, structural characterization, reactivity and catalytic activity of mixed halo/triflate ArI(OTf)(X) species

Both mixed λ³-iodoarenes and λ³-iodoarenes possessing -OTf ligands are coveted for their enhanced reactivities. Here we describe the synthesis, reactivity, and comprehensive characterisation of two new ArI(OTf)(X) species, a class of compound that were previously only invoked as reactive intermediates where X = Cl, F and their divergent reactivity with aryl substrates. A new catalytic system for electrophilic chlorination of deactivated arenes using Cl₂ as the chlorine source and ArI/HOTf as the catalyst is also described.

Synthesis and Structural Verification of an ArI(OTf)2 , NO2 -Ph-I(OTf)2

PhI(OTf)₂ and related ArI(OTf)₂ species have been incorrectly invoked as intermediates in oxidation reactions for many years. We recently established that such compounds did not yet exist but remain an attractive target. Here we describe the synthesis, isolation, and structural characterization of NO₂ -PhI(OTf)_2, which is resistant to decomposition and more reactive than PhI(OTf)(OAc), the species previously misidentified as PhI(OTf)₂ .

Sterically Hindered Tellurium(IV) Catecholate as a Lewis Acid

Sterically hindered tellurium catecholate Te(Cat³⁶)₂ (Cat³⁶ = 3,6-di-tert-butyl-catecholate) was synthesized with the reaction of amorphous Te with 3,6-di-tert-butyl-o-benzoquinone. Adducts of Te(Cat³⁶)₂ with various O- and N-donors were isolated and characterized by means of single-crystal X-ray diffraction along with IR, UV-vis, and NMR (¹H, ¹³C, and ¹²⁵Te) spectroscopies. In the crystal structure of the adduct with 2,2'-bipyridine (bipy), the unprecedented μ-κ²N,N':κ²N,N'-bridging coordination mode of bipy was observed. Various intermolecular interactions Te...O, Te...N, and Te...C in adducts were analyzed using density functional theory calculations and quantum theory of atoms in molecules analysis. The estimated strength for appropriate short contacts varies from 0.9 to 5.3 kcal/mol, and they are attractive and purely non-covalent.

Lewis acid activation of Weiss' reagents ([PhI(Pyr)2]2+) with boranes and isolation of [PhI(4-DMAP)]2

Abstraction of a pyridine ligand from Weiss' reagent ([PhI(Pyr)₂]²⁺) using BF₃-Et₂O was found to activate Weiss' reagent towards electrophilic aromatic substitution reactions. The activated species can be isolated when 4-DMAP is used as the pyridine ligand and was determined to be [PhI(4-DMAP)]²⁺ in solution. The isolated cation was reactive in electrophilic aromatic substitution reactions towards mesitylene, xylene and toluene that Weiss' reagent itself does not react with.

A Sterically Hindered Derivative of 2,1,3-Benzotelluradiazole: A Way to the First Structurally Characterised Monomeric Tellurium-Nitrogen Radical Anion

Interaction of the tetradentate redox-active 6,6'-[1,2-phenylenebis(azanediyl)]bis(2,4-di-tert-butylphenol) (H₄ L) with TeCl₄ leads to neutral diamagnetic compound TeL (1) in high yield. The molecule of 1 has a nearly planar TeN₂ O₂ fragment, which suggests the formulation of 1 as Te^II L^2- , in agreement with the results of DFT calculations and QTAIM and NBO analyses. Reduction of 1 with one equivalent of [CoCp₂ ] leads to quantitative formation of the paramagnetic salt [CoCp₂ ]⁺ [1]^.- , which was characterised by single-crystal XRD. The solution EPR spectrum of [CoCp₂ ]⁺ [1]^.- at room temperature features a quintet due to splitting on two equivalent ¹⁴ N nuclei. Below 150 K it turns into a broad singlet line with two weak satellites due to the splitting on the ¹²⁵ Te nucleus. Two-component relativistic DFT calculations perfectly reproduce the a(¹⁴ N) HFI constants and A_∥ (¹²⁵ Te) value responsible for the low-temperature satellite splitting. Calculations predict that the additional electron in 1^.- is localised mainly on L, while the spin density is delocalised over the whole molecule with significant localisation on the Te atom (≥30 %). All these data suggest that 1^.- can be regarded as the first example of a structurally characterised monomeric tellurium-nitrogen radical anion.

Donor-Acceptor Complexes between 1,2,5-Chalcogenadiazoles (Te, Se, S) and the Pseudohalides CN- and XCN- (X=O, S, Se, Te)

Donor-acceptor (D-A) complexes between 3,4-dicyano-1,2,5-chalcogenadiazoles [chalcogen=Te (1 a), Se (1 b), S (1 c)] and the pseudohalides CN^- and XCN^- (X=O, S, Se, Te) were studied experimentally and theoretically. For 1 a, they were isolated as [K(18-crown-6)][1 a-CN] (2), [K(18-crown-6)][1 a-NCO] (3), [K(18-crown-6)][1 a-SCN] (4), [K(18-crown-6)][1 a-SeCN] (5), and [K][1 a-NCSe] (6) and characterized by X-ray diffraction (XRD), UV/Vis and NMR spectroscopy, and DFT and QTAIM calculations. For 1 b and 1 c, the complexes were not isolated due to unfavorable thermodynamics. In all isolated complexes, the D-A bonds, stabilized by negative hyperconjugation, were longer than the sum of the covalent radii and shorter than the sum of the van der Waals radii of the bonded atoms. In mixtures of 1 a, F^- , and SeCN^- , the complex [1 a-F]^- was selectively formed in accordance with thermodynamics. The reaction of 1 a with SeCN^- and the cyclic trimeric perfluoro-ortho-phenylene mercury afforded the complex [K(18-crown-6)][SCN]⋅(o-C₆ F₄ Hg)₃ , which was characterized by XRD.

A 2,2′-bipyridine coordination complex of [ICl2]+

A straightforward synthesis of a new type of iodine(iii) complex is presented – anN′Nchelated [ICl₂]⁺cation.

Diverse reactions of PhI(OTf)2 with common 2-electron ligands: complex formation, oxidation, and oxidative coupling

The crystal structures of bis-pyridine stabilized iodine dications [PhI(pyr)(2)](2+) are reported as triflate salts, representing the first ligand supported iodine dications to be structurally characterized. The pyridine complexes are susceptible to ligand exchange in reaction with stronger N-based donors such as 4-dimethylaminopyridine. Attempts to extend this reactivity to N-heterocyclic carbene and phosphine ligands, as has been accomplished in the earlier p-block groups, resulted in redox chemistry, with oxidation of the ligands rather than coordination.

Phosphorus(III) cations supported by a PNP pincer ligand and sub-stoichiometric generation of P4 from thermolysis of a nickel insertion product

Neutral, mono-, and dicationic phosphorus(III) compounds are accessible with a supporting PNP pincer ligand (PNP = [4-Me-2-iPr(2)P-C(6)H(3))(2)N]). Reaction of (PNP)H with PCl(3) and nBu(3)N furnished (PNP)PCl(2) (1), which displays a highly temperature-dependent structure in solution. Synthesis and characterization by NMR spectroscopy and X-ray crystallography of Cl/Br-scrambled derivatives, a monocationic derivative [(PNP)PCl][HCB(11)H(11)] (4), and the dicationic derivatives [(PNP)P][OTf](2) (5), [(PNP)P][B(C(6)F(5))(4)](2) (6), [(PNP)P][B(12)Cl(12)] (7) established that 1 not only undergoes several fluxional processes in solution but also possesses a temperature-dependent ground state structure. Reaction of 1 with a Ni(0) source initially leads to a phosphine-phosphinidene complex, followed by thermal generation of P(4).