Tellurium-centered complexes

With soft Lewis acids, phenotellurazines 43 form molecular complexes in which the tellurium center serves as the ligating atom [82DOK(266)1164 85KGS757]. The 1 1 complexes 49 are formed with salts of Hg(II) and Ag(I). PdCb reacts with 43 to give 1 2 complexes 50. Whereas the Hg(II) and Pd(II) complexes are stable on exposure to air, the Ag(I) complexes rapidly decompose when isolated from their solutions. 

The only structurally characterized derivative of a trisimido organophos-phonate anion is the spirocyclic tellurium(IV) complex (19), which is obtained from the interesting redox reaction between PhPCl2 and [Li2Te(N Bu)3 ] 2 [27]. The phosphorus(V)-centered ligands are generated by imide transfer from tellurium to the phosphorus(III) atoms with concomitant reduction of one-half of the tellurium in the Te(IV) reagent to elemental tellurium [27]. 

A large number of tellurium(II)-complexes exist also with an electron-rich three-center bond 12 7). In most complexes the tellurium(II) shows squeire planar four coordination. 

Inversion at sulfur (also selenium and, occasionally, tellurium) coordinated to Pt(II), and indeed to a number of other transition metal centers, e.g., W(0), Re(I), Rh(III), and especially Pt(IV), has been studied extensively over several decades (246). Observation of the kinetics of such processes is often complicated by concurrent changes elsewhere in the complex, for example by hindered rotation about C-S in the square-planar complexes [(XS)2Pt(p-SX)2Pt(SX)2]2 with X = C6F4H, CgF5, C6F4(4-CF3). Resolution of the observed kinetics here indicated barriers (AG ) of between 54 and 59kJmol-1 for inversion at coordinated sulfur, between 40 and 60 kJ mol-1 for the hindered rotation (247). 

The corresponding selenium(IV) derivatives are less stabilized by the three-center, four-electron bonds in the chalcogen(rV) complex than the tellurium(lV) derivatives. As a consequence, the selenium(lV) derivative is more easily reduced than the tellurium(lV) derivative. Diphenylselenium(lV) dibromide (1) undergoes a two-electron reduction with Ep at - - 0.40 V (vs. SCE) while diphenyltellurium(lV) dibromide (2) undergoes a two-electron reduction with at-1-0.05 V (vs. SCE). ... 

DiaUcyl as well as diaryl tellurides behave as monodentate ligands. Consistent with their soft character, their best explored group of complexes involves Pd(II) and Pt(II) centers. A variety of techniques have been applied to the characterization of their solid state and solution stractures. In such square-planar complexes, [MX2(TeR2)2] (M = Pd, Pt X = Cl, Br, I), cis - trans isomerization, intramolecular ligand exchange and tellurium inversion processes have all been observed by detailed far-infrared and variable-temperature NMR studies (see Refs. 14,15,17,3 5 for a more detailed review of the subject). 

The reaction of bromopentacarbonylmanganese(I) and of pentacarbonylchlororhenium(I) with bis[trimethylstannyl] tellurium produced dimeric carbonyl complexes with two trimethylstannyltelluro groups bridging the metal centers. ... 

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