The Reactions of Tellurium Tetrahalides with Triphenylphosphine under Ambient Conditions

The reactions of tellurium tetrahalides and triphenylphosphine in tetrahydrofuran have been carried out under ambient
conditions and afford {(Ph3PO)2H}2[Te2X10] [X = Cl (1), Br (2)] and {(Ph3PO)3(OH3})2[TeI6] (4). The X-ray structures
of 1 and 2 show that they are isostructural and contain discrete [Te2X10]2- anions exhibiting octahedral coordination
around both tellurium atoms with one shared edge and {Ph3POH···OPPh3}+ cations that show strong hydrogen
bonds (the O···O distances are 2.399 and 2.404 Å for 1 and 2, respectively). The compound 4 is built up with
discrete octahedral hexaiodotellurate anions and {(Ph3PO)3(OH3)}+ cations. The reaction of TeBr4 and PPh3 also
results in the formation of formally zwitterionic Ph3PO(CH2)4TeBr4 (3). This reaction involves an unprecedented
THF ring opening in which the oxygen atom becomes bonded to the phosphorus atom of triphenylphosphine and
the carbon atom at the other end of the five-atomic chain becomes bonded to the tellurium atom of TeBr4. The ring
opening of the solvent THF is also taking place in the reaction involving tellurium tetraiodide, as indicated by the
formation of C4H8TeI2 (5). The reaction may initially lead to Ph3PI2 that reacts with THF yielding Ph3PO and ICH2(CH2)2CH2I. The latter species reacts with elemental tellurium producing 5. Depending on the conditions upon crystallization,
two polymorphs of C4H8TeI2 (5a and 5b) are observed. While the molecular structures of the two forms are virtually
identical, their packing and intermolecular contacts are different. Two further minor products (6a and 6b) were
isolated in the reaction of TeI4 and PPh3:  Both are formally 1:1 adducts of 5 and TeI4, but they differ considerably
in their structures. 6a can be formulated as {C4H8TeI+}2[Te2I102-] and 6b as {C4H8TeI+}2(TeI3+)2(I-)4. The latter
compound exhibits framework similar to that of the tetramers in γ- and δ-TeI4.