Synthesis and Characterization of HN(SPiPr2)(SePPh2) and [Te{N(SPiPr2)(SePPh2)}2]

A square-planar tellurium(II) complex withTe,Te′-chelating ligands

While exploring the chemistry of tellurium-containing dichalcogenidoimidodiphosphinate ligands, the first all-tellurium member of a series of related square-planarEII(E′)4complexes (EandE′ are group 16 elements), namely bis(P,P,P′,P′-tetraphenylditelluridoimidodiphosphinato-κ2Te,Te′)tellurium(II) (systematic name: 2,2,4,4,8,8,10,10-octaphenyl-1λ3,5,6λ4,7λ3,11-pentatellura-3,9-diaza-2λ5,4λ5,8λ5,10λ5-tetraphosphaspiro[5.5]undeca-1,3,7,9-tetraene), C48H40N2P4Te5, was obtained unexpectedly. The formally TeIIcentre is situated on a crystallographic inversion centre and isTe,Te′-chelated to two anionic [(TePPh2)2N]−ligands in ananticonformation. The central TeII(Te)4unit is approximately square planar [Te—Te—Te = 93.51 (3) and 86.49 (3)°], with Te—Te bond lengths of 2.9806 (6) and 2.9978 (9) Å.

Synthesis, NMR characterisation and X-ray structures of mixed chalcogenido PNP ligands containing tellurium: crystal structures of SeiPr2PNP(H)iPr2 and [NaN(EPiPr2)2]infinity (E = Se, Te)

Reaction of HN(PiPr2)2 with one equivalent of selenium in hexane at room temperature yields the monoselenide as the P-H tautomer Se=PiPr2-N=P(H)iPr2 (2b). Deprotonation of 2b with n butyllithium in the presence of TMEDA at -78 degrees C followed by addition of tellurium produces the air-sensitive, mixed chalcogenido complex [(TMEDA)Li(SePiPr2)(TePiPr2)N] (8Li) in >97% purity after recrystallisation. Similarly, deprotonation of Te=PiPr2-N=P(H)iPr2 (2c), followed by addition of sulfur, gives the sulfur analogue [(TMEDA)Li(SPiPr2)(TePiPr2)N] (7Li) in >99% purity. The symmetrical complexes [(TMEDA)Li(SePiPr2)2N] (4Li) and [(TMEDA)Li(TePiPr2)2N] (5Li) are produced by similar methods. Compounds 2b, 4Li, 5Li, 7Li and 8Li were characterised in solution by multinuclear (1H, 31P, 77Se and 125Te) NMR spectroscopy and their solid-state structures were determined by X-ray crystallography. The X-ray crystal structures of the polymeric chains [NaN(EPiPr2)2]infinity (4Na, E = Se and 5Na, E = Te) are also reported.

The nature of the chemical bond in linear three-body systems: from i3- to mixed chalcogen/halogen and trichalcogen moieties

The 3 centre-4 electrons (3c-4e) and the donor/acceptor or charge-transfer models for the description of the chemical bond in linear three-body systems, such as I(3) (-) and related electron-rich (22 shell electrons) systems, are comparatively discussed on the grounds of structural data from a search of the Cambridge Structural Database (CSD). Both models account for a total bond order of 1 in these systems, and while the former fits better symmetric systems, the latter describes better strongly asymmetric situations. The 3c-4e MO scheme shows that any linear system formed by three aligned closed-shell species (24 shell electrons overall) has reason to exist provided that two electrons are removed from it to afford a 22 shell electrons three-body system: all combinations of three closed-shell halides and/or chalcogenides are considered here. A survey of the literature shows that most of these three-body systems exist. With some exceptions, their structural features vary continuously from the symmetric situation showing two equal bonds to very asymmetric situations in which one bond approaches to the value corresponding to a single bond and the second one to the sum of the van der Waals radii of the involved atoms. This indicates that the potential energy surface of these three-body systems is fairly flat, and that the chemical surrounding of the chalcogen/halogen atoms can play an important role in freezing different structural situations; this is well documented for the I(3) (-) anion. The existence of correlations between the two bond distances and more importantly the linearity observed for all these systems, independently on the degree of their asymmetry, support the state of hypervalency of the central atom.