The ligand chemistry of tellurium

Experimental and computational investigation on the formation pathway of [RuCl2(CO)2(ERR')2] (E = S, Se, Te; R, R' = Me, Ph) from [RuCl2(CO)3]2 and ERR'

The pathways to the formation of the series of [RuCl₂(CO)₂(ERR')₂] (E = S, Se, Te; R, R' = Me, Ph) complexes from [RuCl₂(CO)₃]₂ and ERR' have been explored experimentally in THF and CH₂Cl₂, and computationally by PBE0-D3/def2-TZVP calculations. The end-products and some reaction intermediates have been isolated and identified by NMR spectroscopy, and their crystal structures have been determined by X-ray diffraction. The relative stabilities of the [RuCl₂(CO)₂(ERR')₂] isomers follow the order cct > ccc > tcc > ttt ≈ ctc (the terms c/t refer to cis/trans arrangement of the ligands in the order of Cl, CO, and ERR'). The yields were rather similar in both solvents, but the reactions were significantly faster in THF than in CH₂Cl₂. The highest yields were observed for the telluroether complexes, and the yields decreased with lighter chalcogenoethers. PBE0-D3/def2-TZVP calculations indicated that the reaction path is independent of the nature of the solvent. The substitution of one CO ligand of the intermediate [RuCl₂(CO)₃(ERR')] by the second ERR' shows the highest activation barrier and is the rate-determining step in all reactions. The observed faster reaction rate in THF than in CH₂Cl₂ upon reflux can therefore be explained by the higher boiling point of THF. At room temperature the reactions in both solvents proceed equally slowly. When the reaction is carried out in THF, the formation of [RuCl₂(CO)₃(THF)] is also observed, and the reaction may proceed with the substitution of THF by ERR'. The formation of the THF complex, however, is not necessary for the dissociation of the [RuCl₂(CO)₃]₂. Thermal energy at room temperature is sufficient to cleave one of the bridging Ru-Cl bonds. The intermediate thus formed undergoes a facile reaction with ERR'. This mechanism is viable also in non-coordinating CH₂Cl₂.

The First Metal Complexes of 1,4-Oxatellurane: Synthesis and Crystal Structure of its Platinum(II) complex

The palladium(II) and platinum(II) complexes of 1,4-oxatellurane (L), having the composition [MCl2L2], are synthesized and characterized spectroscopically and structurally (Pt complex only; Pt–Cl 2.3169(9) Å; Pt–Te 2.5945(3) Å) for the first time.

Recent advances in the self-assembly of polynuclear metal–selenium and –tellurium compounds from 14–16 reagents

The use of reagents containing bonds between group 14 elements and Se or Te for the self-assembly of polynuclear metal–chalcogen compounds is covered. Background material is briefly reviewed and examples from the literature are highlighted from the period 2007–2017. Emphasis is placed on the different classes of 14–16 precursors and their application in the targeted synthesis of metal–chalcogen compounds. The unique properties arising from the combination of specific 14–16 precursors, metal atoms, and ancillary ligands are also described. Selected examples are chosen to underline the progress in (i) controlled synthesis of heterometallic (ternary) chalcogen clusters, (ii) chalcogen clusters with organic functionalized surfaces, and (iii) crystalline open-framework metal chalcogenides.

Bis(6-Diphenylphosphinoacenaphth-5-yl)Telluride as a Ligand toward Manganese and Rhenium Carbonyls

The reaction of the previously known bis(6-diphenylphosphinoacenaphthyl-5-)telluride (6-Ph₂P-Ace-5-)₂Te (IV) with (CO)₅ReCl and (CO)₅MnBr proceeded with the liberation of CO and provided fac-(6-Ph₂P-Ace-5-)₂TeM(X)(CO)₃ (fac-1: M = Re, X = Cl; fac-2: M = Mn, X = Br), in which IV acts as bidentate ligand. In solution, fac-1 and fac-2 are engaged in a reversible equilibrium with mer-(6-Ph₂P-Ace-5-)₂TeM(X)(CO)₃ (mer-1: M = Re, X = Cl; mer-2: M = Mn, X = Br). Unlike fac-1, fac-2 is prone to release another equivalent of CO to give (6-Ph₂P-Ace-5-)₂TeMn(Br)(CO)₂ (3), in which IV serves as tridentate ligand.

Chromium-manganese selenide carbonyl complexes: paramagnetic clusters and relevance to C=O activation of acetone

The paramagnetic even-electron cluster, [Et(4)N](2)[Se(2)Cr(3)(CO)(10)], was found to react readily with Mn(CO)(5)Br in acetone to produce two unprecedented mixed chromium-manganese selenide carbonyl complexes, [Et(4)N][Me(2)CSe(2){Mn(CO)(4)}{Cr(CO)(5)}(2)] ([Et(4)N][1]) and [Et(4)N](2)[Se(2)Mn(3)(CO)(10){Cr(CO)(5)}(2)] ([Et(4)N](2)[2]). X-ray crystallographic analysis showed that anion 1 consisted of two Se-Cr(CO)(5) moieties, which were further bridged by one isopropylene group and one Mn(CO)(4) moiety. The dianionic cluster 2 was shown to display a Se(2)Mn(3) square-pyramidal core with each Se atom externally coordinated by one Cr(CO)(5) group. The formation of complex 1, presumably via C=O activation of acetone, was further facilitated by acidification of the reaction of [Et(4)N](2)[Se(2)Cr(3)(CO)(10)] with Mn(CO)(5)Br in acetone. Complex 1 readily transformed into 2 upon treatment with Mn(2)(CO)(10) in a KOH/MeOH/MeCN solution. Cluster 2 was a 51-electron species, which readily converted to the known 49-electron cluster [Se(2)Mn(3)(CO)(9)](2-) upon heating and bubbling with CO. Magnetic studies of the even-electron cluster, [Et(4)N](2)[Se(2)Cr(3)(CO)(10)], and the odd-electron species, [Et(4)N](2)[2] and [PPN](2)[Se(2)Mn(3)(CO)(9)], were determined by the SQUID measurement to have 2, 3, and 1 unpaired electrons, respectively. In addition, the nature and formation of complexes 1 and 2 are discussed, and the magnetic properties and electrochemistry of [Se(2)Cr(3)(CO)(10)](2-), 2, and [Se(2)Mn(3)(CO)(9)](2-) were further studied and elucidated by molecular orbital calculations at the PW91 level of density functional theory.

Tellurium: an element with great biological potency and potential

Tellurium has long appeared as a nearly 'forgotten' element in Biology, with most studies focusing on tellurite, tellurate and a handful of organic tellurides. During the last decade, several discoveries have fuelled a renewed interest in this element. Bioincorporation of telluromethionine provides a new approach to add heavy atoms to selected sites in proteins. Cadmium telluride (CdTe) nanoparticles are fluorescent and may be used as quantum dots in imaging and diagnosis. The antibiotic properties of tellurite, long known yet almost forgotten, have attracted renewed interest, especially since the biochemical mechanisms of tellurium cytotoxicity are beginning to emerge. The close chemical relationship between tellurium and sulfur also transcends into in vitro and in vivo situations and provides new impetus for the development of enzyme inhibitors and redox modulators, some of which may be of interest in the field of antibiotics and anticancer drug design.