Pushing the Boundary of Covalency in Lanthanoid-Tellurium Bonds: Insights from the Synthesis, Molecular and Electronic Structures of Low-Coordinate, Monomeric Europium(II) and Ytterbium(II) Tellurolates.

Owing to the strict hard/soft dichotomy between the lanthanoids and tellurium atoms, and the strong affinity of lanthanoid ions for high coordination numbers, low-coordinate, monomeric lanthanoid tellurolate complexes have remained elusive as compared to the lanthanoid complexes with lighter group 16 elements (O, S, and Se). This makes the development of suitable ligand systems for low-coordinate, monomeric lanthanoid tellurolate complexes an appealing endeavor. In a first report, a series of low-coordinate, monomeric lanthanoid (Yb, Eu) tellurolate complexes were synthesized by utilizing hybrid organotellurolate ligands containing N-donor pendant arms. The reaction of bis[2-((dimethylamino)methyl)phenyl] ditelluride, 1 and 8,8'diquinolinyl ditelluride, 2 with Ln0 metals (Ln=Eu, Yb) resulted in the formation of monomeric complexes [LnII (TeR)2 (Solv)2 ] [R=C6 H4 -2-CH2 NMe2 ] [3: Ln=Eu, Solv=tetrahydrofuran; 4: Ln=Eu, Solv=acetonitrile; 5: Ln=Yb, Solv=tetrahydrofuran; 6: Ln=Yb, Solv=pyridine] and [EuII (TeNC9 H6 )2 (Solv)n ] (7: Solv=tetrahydrofuran, n=3; 8: Solv=1,2-dimethoxyethane, n=2), respectively. Complexes 3-4 and 7-8 represent the first sets of examples of monomeric europium tellurolate complexes. The molecular structures of complexes 3-8 are validated by single-crystal X-ray diffraction studies. The electronic structures of these complexes were investigated using Density Functional Theory (DFT) calculations, which revealed appreciable covalency between the tellurolate ligands and lanthanoids.

Carbene chemistry of arsenic, antimony, and bismuth: origin, evolution and future prospects.

The discovery of the first isolable N-heterocyclic carbene in 1991 ushered in a new era in coordination chemistry. The remarkable bonding properties of carbenes have led to their rapid proliferation as auxiliary ligands for a wide range of transition metals and main group elements. In the case of group 15, while carbene-stabilized nitrogen and phosphorus compounds are extensively studied, the scope of research has shrunk significantly from arsenic to bismuth. This is essentially attributed to the decrease in stability of the C-E bond upon descending the group. Even so, modulating the carbene backbone or introducing alternative synthetic strategies not only alleviates the stability issues but also offers promising results in terms of the bonding and reactivities of these compounds. The purpose of the present perspective is to provide a comprehensive overview of the origins and development of carbene chemistry of arsenic, antimony, and bismuth, as well as to highlight the future prospects of this field.

Structure of a diorganotelluroxonium(IV) cation, {[2,6-(CH2NMe2)2C6H3Te(µ-O)]2}2+, with the tri-chlorido-(dimethyl sulfoxide)-platinum(II) anion.

In the title salt, di-µ-oxido-bis-{2,6-bis-[(di-methyl-amino)-meth-yl]phenyl-κC 1}tellurium(-IV) bis[tri-chlorido-(dimethyl sulfoxide-κS)platinate(II)], (C24H38N4O2Te2)[PdCl3(C2H6OS)]2, which crystallizes in the triclinic space group P , each Te atom is in a distorted five-coordinated TeO2N2C square-pyramidal geometry (τ values of 0.026 and 0.001) with the C atoms of the phenyl rings occupying the apical positions. The phenyl rings in the [C24H38N4O2Te2]2+ cation are in a cis arrangement to enable this species to participate in Te⋯Cl cation-anion inter-actions. There are also C-H⋯O inter-actions involving the dimethyl sulfoxide ligands and numerous cation-anion and anion-anion C-H⋯Cl inter-actions, which link the ions into a complex three-dimensional array.

Structural characterization of the derivatives of bis{[2,6-(dimethylamino)methyl]phenyl} selenide with palladium(II) and mercury(II).

The intramolecularly coordinated homoleptic diorgano selenide bis{2,6-bis[(dimethylamino)methyl]phenyl} selenide, C24H38N4Se or R2Se, where R is 2,6-(Me2NCH2)2C6H3, 14, was synthesized and its ligation reactions with PdII and HgII precursors were explored. The reaction of 14 with SO2Cl2 and K2PdCl4 resulted in the formation of the meta C-H-activated dipalladated complex {µ-2,2'-bis[(dimethylamino)methyl]-4,4'-bis[(dimethylazaniumyl)methyl]-3,3'-selanediyldiphenyl-κ4C1,N2:C1',N2'}bis[dichloridopalladium(II)], [Pd2Cl4(C24H38N4Se)] or [{R(H)PdCl2}2Se], 15. On the other hand, when ligand 14 was reacted with HgCl2, the reaction afforded a dimercurated selenolate complex, {µ-bis{2,6-bis[(dimethylamino)methyl]benzeneselanolato-κ4N2,Se:Se,N6}-µ-chlorido-bis[chloridomercury(II)], [Hg2(C12H19N2Se)Cl3] or RSeHg2Cl3, 16, where two HgII ions are bridged by selenolate and chloride ligands. In palladium complex 15, there are two molecules located on crystallographic twofold axes and within each molecule the Pd moieties are related by symmetry, but there are still two independent Pd centers. Mercury complex 16 results from the cleavage of one of the Se-C bonds to form a bifurcated SeHg2 moiety with the formal charge on the Se atom being -1. In addition, one of the Cl ligands bridges the two Hg atoms and there are two terminal Hg-Cl bonds. Each Hg atom is in a distorted environment which can be best described as a T-shaped base with the bridging Cl atom in an apical position, with several angles close to 90° and with one angle much larger and closer to 180°.

Isolation of the novel example of a monomeric organotellurinic acid.

The stoichiometrically controlled alkaline hydrolysis of 4, (ppy)TeCl3, [ppy = 2-(2'-pyridyl)phenyl] afforded the partially hydrolyzed µ-oxo-bridged dinuclear telluroxane 5, [(ppyTeCl2)2(µ-O)] and a novel example of an Intramolecular Chalcogen Bonding (IChB) stabilized, monomeric organotellurinic acid 6, (ppy)Te(O)OH. The oxidation of diaryl ditelluride 7, (ppyTe)2 using H2O2 resulted in the isolation of µ-oxo-bridged dimethyl ester 8, [(ppy)Te(O)(OH)(OMe)]2(O). The molecular structures of 4-6 and 8 are unambiguously authenticated by single crystal X-ray diffraction studies. The electronic structure of monomeric tellurinic acid 6 is investigated using DFT calculations. The Natural Bond Order (NBO) analysis, in corroboration with Atoms in Molecules (AIM) analysis reveals that tellurinic acid 6 is stabilized by σ-hole participation of the tellurium atom with the pyridyl N-atom resulting in strong electrostatic interactions between the N and Te atoms.

Oxidation behavior of intramolecularly coordinated unsymmetrical diorganotellurides: isolation of novel tetraorganoditelluronic acids, [RR'Te(µ-O)(OH)2]2.

The oxidation reaction of unsymmetrical diorganotellurides, namely, bis[2-{(dimethylamino)methyl}aryl]tellurides [aryl = phenyl (6), 2-methylphenyl (7), 2,6-dimethylphenyl (8) and 2,6-diisopropylphenyl (9)] with meta-chloroperbenzoic acid afforded the first examples of tetraorganoditelluronic acids, [RR'Te(µ-O)(OH)2]2, where R = 2-NMe2CH2C6H4, R' = C6H5 (10), 2-MeC6H4 (11), 2,6-MeC6H3 (12) and 2,6-iPrC6H3 (13). The structures of tetraorganoditelluronic acids 10-13 were authenticated by single crystal X-ray diffraction studies. From the molecular structures of 10-13, it was observed that the sp3 N-donor atoms, which were initially involved in intramolecular TeN bonding interactions in diorganotellurides 6-9, did not interact with the tellurium atoms in tetraorganoditelluronic acids 10-13. The 125Te chemical shifts for 10-13 were considerably downfield shifted as compared with the values observed for the corresponding tellurides 6-9. The relative stabilities of the tetraorganoditelluronic acids 10-13 with respect to their lighter analogues (S and Se) have been assessed using DFT calculations.

Hypervalent organoselenium compounds stabilized by intramolecular coordination: synthesis and crystal structures.

Two novel hypervalent selenium(IV) compounds stabilized by intramolecular interactions, namely 6-phenyl-6,7-dihydro-5H-2,3-dioxa-2aλ4-selenacyclopenta[hi]indene, C14H12O2Se, 14, and 5-phenyl-5,6-dihydro-4H-benzo[c][1,2]oxaselenole-7-carbaldehyde, C14H12OSe2, 15, have been synthesized by the reaction of 2-chloro-1-formyl-3-(hydroxymethylene)cyclohexene with in-situ-generated disodium diselenide (Na2Se2). The title compounds were characterized by FT-IR spectroscopy, ESI-MS, and single-crystal X-ray diffraction studies. For 14, there is whole-molecule disorder, with occupancies of 0.605 (10) and 0.395 (10), a double bond between C and Se, and the five-membered selenopentalene rings are coplanar. The packing is stabilized by π-π stacking interactions involving one of the five-membered Se/C/C/C/O rings [centroid-centroid (Cg...Cg) distance = 3.6472 (18) Šand slippage = 1.361 Å], as well as C-H...π interactions involving a C-H group and the phenyl ring. In addition, there are bifurcated C-H...Se,O interactions which link the molecules into ribbons in the c direction. For 15, the C-Se bond lengths are longer than those of 14. The two five-membered rings are coplanar. There are no π-π or C-H...π interactions; however, molecules are linked by C-H...O interactions into centrosymmetric dimers, with graph-set notation R22(16).