Experimental and Theoretical Investigations of the Redox Behavior of the Heterodichalcogenido Ligands [(EPⁱPr₂)(TePⁱPr₂)N]⁻(E = S, Se): Cyclic Cations and Acyclic Dichalcogenide Dimers

Abstract

The two-electron oxidation of the lithium salts of the heterodichalcogenidoimidodiphosphinate anions [(EP i Pr 2 )(TeP i Pr 2 )N] -(1a, E ) S; 1b, E ) Se) with iodine yields cyclic cations [(EP i Pr 2 )(TeP i Pr 2 )N] + as their iodide salts [(SP i Pr 2 )(TeP i Pr 2 )N]I (2a) and [(SeP i Pr 2 )(TeP i Pr 2 )N]I (2b). The five-membered rings in 2a and 2b both display an elongated E-Te bond as a consequence of an interaction between tellurium and the iodide anion. Oneelectron reduction of 2a and 2b with cobaltocene produces the neutral dimers (EP i Pr 2 NP i Pr 2 Te-) 2 (3a, E ) S; 3b, E ) Se), which are connected exclusively through a Te-Te bond. Two-electron reduction of 2a and 2b with 2 equiv of cobaltocene regenerates the corresponding dichalcogenidoimidodiphosphinate anions as ion-separated cobaltocenium salts Cp 2 Co[(EP i Pr 2 )(TeP i Pr 2 )N] (4a, E ) S; 4b, E ) Se). The ditellurido analogue Cp 2 Co[(TeP i Pr 2 ) 2 N] (4c) has been prepared in the same manner for comparison. Density functional theory calculations reveal that the preferential interaction of the iodide anion with tellurium is determined by the polarization of the lowest unoccupied molecular orbital [σ*(E-Te)] of the cations in 2a and 2b toward tellurium and that the formation of the dimers 3a and 3b with a central Te-Te linkage is energetically more favorable than the structural isomers with either E-Te or E-E bonds. Compounds 2a, 2b, 3a, 3b, 4a, 4b, and 4c have been characterized in solution by multinuclear NMR spectroscopy and in the solid state by X-ray crystallography.

Experimental and Theoretical Investigations of the Contact Ion Pairs Formed by Reactions of the Anions [(EPR2)2N]− (R = iPr, tBu; E = S, Se) with the Cations [(TePR2)2N]+ (R = iPr, tBu)

“…As noted earlier, the known heterodichalcogenide dimers are exclusively obtained as ditellurides. 38 However, it is not as straightforward to rationalize why 7b and 7c adopt a monodentate coordination mode.…”

“…36,37 For the heterodichalcogenidoimidodiphosphinate (2, E ≠ E′), the resulting dimer is exclusively obtained as a ditelluride with a Te-Te interaction rather than an E-E or E-Te interaction. 38 The second bonding mode is best described as a spirocyclic contact ion pair (5) in which a dichalcogenido anion is chelated to one of the chalcogen atoms of the corresponding cation. 37 To date this structural type has been limited to the all-tellurium system with R = t Bu.…”

Organophosphorus–Tellurium Chemistry: From Fundamentals to Applications

“…158 This protocol is also the preferred procedure for the preparation of lithium derivatives of the mixed-chalcogen anions [N(P i Pr 2 E)(P i Pr 2 + with cobaltocene. 160 The related mixedchalcogen systems Cp 2 Co[N(P i Pr 2 E)(P i Pr 2 Te)] are prepared by using a similar synthetic protocol. …”

New Insights into the Chemistry of Imidodiphosphinates from Investigations of Tellurium-Centered Systems

“…DFT towards the more electropositive tellurium atom when E = S, Se resulting in stronger TeTe overlap. 11 The elongation of the central chalcogen-chalcogen bond in the diselenides 4b and 4b ′ is ca. 6 % and that in the disulfide 4c′ is only 2 %, suggesting better overlap of the two radical SOMOs for the lighter chalcogens We note, however, that the markedly different conformations of acyclic DCs is likely to be a contributing factor.…”

“…13 The mixed chalcogen systems 6c and 6d are prepared in a similar manner. 11 The hexafluoroantimonate salts 7a,b are produced by metathesis of the corresponding iodide salts with Ag[SbF6] (Scheme 2). 14 The salts 6a and 6b are comprised of a five-membered cyclic cation [N(P i Pr2E)2] + and an iodide counterion that interacts with one of the chalcogens to form an infinite chain structure (Figure 2).…”