Mechanistic Aspects of the Thermal and Photochemical Interconversion of Permethylscandocene Tellurolates and Tellurides. X-ray Structures of (C5Me5)2ScTeCH2C6H5, [(C5Me5)2Sc]2(.mu.-Te), and [(C5Me5)2Sc]2(.mu.-Se)

Warren E Piers; Daniel J Parks; Leonard R MacGillivray; Michael J Zaworotko

doi:10.1021/om00023a067

Treatment of Cp*2ScR (Cp* = η5-C5Me5; R = CH2SiMe3, CH2C6H5, erythro-CH(D)CH(D)-t-C4H9, CH2CH(D)CH2CH2CH=CMe2, C6H5, CH2(c-C5H9)) with 1 equiv of elemental tellurium or Te=P-n-Bu3 yields the tellurolates Cp*2ScTeR (1a-e,g) in moderate to good yields (31–71%). The tellurolates are monomeric, as inferred from the X-ray structure of 1b (Sc-Te = 2.8337(14) Å; Sc‒Te‒C = 121.61(21)°). Insertion of elemental selenium into the Sc‒C bond of Cp*2ScCH2SiMe3 produces selenolate 3 (55%). Reaction of 0.5 equiv of tellurium or selenium with the deuteride Cp*2ScD results in elimination of D2 and production of chalcogenide dimers [Cp*2Sc]2(μ-E) (E = Te (2), Se (4)). Evidence that the production of 2 proceeds via Cp*2ScTeD is presented. The X-ray structures of 2 (Sc‒Te = 2.7528(12) Å Sc-Te-Sca = 172.07(5)°) and 4 (Se‒Sc = 2.5425(16) Å Sc‒Se‒Sca = 173.74(10)°) were performed and are reported for comparison. Telluride dimer 2 was also produced via the thermal (70–110 °C) or photochemical (λ > 290 nm) extrusion of TeR2 from tellurolates 1a-d. Further thermal reactions between 2 and TeR2 were observed at higher temperatures, leading to a new scandium telluride of empirical formula Cp*ScTe. Experiments utilizing tellurolates 1c,d indicate that both the thermal and photochemical eliminations of TeR2 proceed without involving Te‒C bond cleavage, leading to R• intermediates. Photochemical reactions between 2 and TeR2 substrates showed that the elimination process is photochemically reversible, leading to varying mixtures of compounds 1, 2, and TeR2, depending on the nature of R. Use of Te[(CH2)4CH=CH2]2, which contains an alkyl group sensitive to the presence of R•, shows cyclization in the 5-hexenyl group leading to 1g, indicating the involvement of radicals in the back-photoreaction. The presence of a photostationary equilibrium in these systems is further evidenced in the slow conversion of Cp*2ScTe(CH2)4CH=CH2 (1f) to 1g over prolonged irradiation periods. Comparison of the UV‒visible spectra and the photochemistry associated with these tellurium compounds with their selenium congeners indicates that the primary photoevents in these reactions involve Te → Sc ligand to metal charge-transfer absorptions. Crystallographic data for 1b, 2, and 4 are as follows: 1b, monoclinic, space group P21/c, a = 14.932(5) Å, b = 10.8122(8) Å, c = 17.496(8) Å, β = 113.64°, V = 2587.5(15) Å3, Z = 4, R = 0.041, Rw = 0.038; 2, tetragonal, space group P421c, a = 15.0324(7) Å, c = 18.8884(14) Å, V = 4268.3(4) Å3, Z = 4, R = 0.040, Rw = 0.034; 4, tetragonal, space group P421c, α = 14.7663(12) Å, c = 19.101(4) Å, Z = = 4, V = 4164.9(9) Å3, R = 0.050, Rw = 0.043. © 1994, American Chemical Society. All rights reserved.

Mechanistic Aspects of the Thermal and Photochemical Interconversion of Permethylscandocene Tellurolates and Tellurides. X-ray Structures of (C5Me5)2ScTeCH2C6H5, [(C5Me5)2Sc]2(.mu.-Te), and [(C5Me5)2Sc]2(.mu.-Se)

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