A planar dianionic ditelluride and a cyclic tritelluride supported by P₂N₂rings

Abstract

with a planar P 6 E 6 (E = S, Se) framework in which dichalcogenido (-E-E-) groups are linked by perpendicular 20 P V 2 N 2 rings. 5 The synthesis of these polychalcogen macrocycles involves the two-electron oxidation of the dianions 1a and 1b with I 2. We now report a detailed investigation of the oxidation of the tellurium analogue 1c that provides important insights into the initial oxidation process, as well as a notable difference in the 25 final outcome of the oxidation compared to that observed for 1a and 1b. Specifically, we have identified and structurally characterised (a) the dianionic ditelluride [Te(, with an unusual planar conformation, as the product of one-electron oxidation of 1c and (b) the cyclicas the result of further oxidation. DFT calculations were carried out in order to determine the reason(s) for the unusual planarity of the PTeTeP unit in the ditelluride 2.The oxidation of the dianion 1c (as its dilithium derivative)with a one-half molar equivalent of I 2 led to the isolation of extremely sensitive black crystals, which were identified by Xray crystallography as [Li(tmeda)] 2 2 (Eq. 1). 7 As depicted in Fig. 1 heteroatom-tellurium interactions and (TpsiTe) 2 for which the antiperiplanar conformation is imposed by the bulky substituents. 10 The Te1···Te2' distance in [Li(tmeda)] 2 2 (3.884 Å) is shorter than the sum of van der Waals radii for Te (4.12 Å).13 Moreover, the closely related neutral ditelluride 60 [( t BuNH)P(μ-N t Bu) 2 P(N t Bu)Te] 2 (4), which has a similar steric environment for the Te-Te linkage, exhibits a dihedral angle of −123.8° and a Te-Te bond length of 2.7204(9) Å (Fig. S1).14 In view of these observations, DFT calculations were carried out to probe whether the conformation of [Li(tmeda)] 2 2 is stabilized by 65 intramolecular Te1···Te2' secondary bonding interactions (3.884 Å). Satisfactory structures were obtained from geometry optimizations (PBE-D3, TZP, ZORA) for planar and synclinal models of [Li(tmeda)] 2 2 and 4 simplified using Me groups in lieu of t Bu. In both instances the planar conformations were higher in 70 energy, by 8 and 37 kJ mol -1 for the models of [Li(tmeda)] 2 2 and 4, respectively. Preferred P-Te-Te-P torsion angles are 98° for the former and 90° for the latter. The small difference of energy suggests that the conformation observed in the crystal structure of [Li(tmeda)] 2 2 is imposed by packing forces. Further analysis on 75 the electronic structures of the [Li(tmeda)] 2 2 models failed to identify a particular orbital interaction or contribution from dispersion that would help stabilize the antiperiplanar geometry.

Tellurium: a maverick among the chalcogens

“…As depicted in Fig. 7 Although it is highly insoluble in common solvents, microtubular tellurium crystals can be grown from ethylenediamine; 10a hexagonal grey tellurium is also very soluble in a thiol-amine solvent mixture, presumably because the intermolecular contacts are disrupted in these solvents.…”

Guest Binding via N−H⋅⋅⋅π Bonding and Kinetic Entrapment by an Inorganic Macrocycle

“…[20][21][22][23][24][25][26][27][28][29] Of particular interest is the pentameric host macrocycle 1 (Figure 1), toroidal shape,l arge void volume, endo-cyclic N-H functionalities,a nd exo-cyclic t Bu groups of which make it ahighly unusual, sterically hindered H-bonding host. [20][21][22][23][24][25][26][27][28][29] Of particular interest is the pentameric host macrocycle 1 (Figure 1), toroidal shape,l arge void volume, endo-cyclic N-H functionalities,a nd exo-cyclic t Bu groups of which make it ahighly unusual, sterically hindered H-bonding host.…”

“…[17][18][19] Key advantages of inorganic anion receptors over organic counterparts are their inherently more polar nature and the ease by which their proton acidities can be modulated.Thehigh bond energy of PÀNs ingle bonds and their low polarity underpin the stability of adiverse range of previously reported phosphazane compounds,and provide agood foundation for the development of anew range of robust inorganic macrocycles. [20][21][22][23][24][25][26][27][28][29] Of particular interest is the pentameric host macrocycle 1 (Figure 1), toroidal shape,l arge void volume, endo-cyclic N-H functionalities,a nd exo-cyclic t Bu groups of which make it ahighly unusual, sterically hindered H-bonding host. Thehost properties of 1 should differ significantly from organic counterparts,e specially given the greater polarity of these P À N-bonded frameworks.Herein, we show that the highly polar nature of the binding site and the sterically congested periphery of 1 leads to unique types of host-guest binding involving NÀH···p-CX (X = CH, N, P) hydrogen bonding to organic and inorganic guests.W ea lso show that oxidation of the phosphorus periphery of 1 can be used to kinetically entrap anions within the macrocycle.T his produces chemically irreversible binding of Cl À and I À anions using acombination of hydrogen bonding and steric encasement, which results in better effective binding of these halides than in any organic or metal-organic architecture.Direct access to 1,w hich was previously prepared by ac omplicated two-step procedure involving the use of gaseous NH 3 ,i sp rovided here by an ew method wherein the cyclodiphosphazane [ClP(m-N t Bu)] 2 (A)iscombined with LiNH 2 in the presence of excess anhydrous LiI, followed by removal of the encapsulated iodide anion (Figure 2a and Section S2 in the Supporting Information).…”

Organophosphorus–Tellurium Chemistry: From Fundamentals to Applications

“…Two intermediates have been isolated and structurally characterized, viz. the planar dianionic ditelluride 66 183 and the spirocyclic dianion 67 with a central Te 5 motif (Figure 31). 187 The final product is the cyclic tritelluride 68 ( Figure 30).…”

“…187 The final product is the cyclic tritelluride 68 ( Figure 30). 183 The complex [Li(TMEDE)] 2 66 is a rare example of a planar ditelluride. In this case, the planarity is attributed to packing effects, 183 however a planar conformation may also be imposed either by very bulky substituents or via intramolecular heteroatom-tellurium interactions.…”