Competitive Te-Te and C-Te bond cleavage in the oxidative addition of diaryl and dialkyl ditellurides to Pt(0) centers

The oxidative addition reaction of ditellurides R2Te2 [R = Bu-n, Ph, Th (2-thienyl, C4H3S)] to [Pt(eta(2)-nb)( dppn)] (nb = norbornene, dppn = 1,2-bis(diphenylphosphano)naphthalene) was found to afford [Pt(TeR)(2)(dppn)] [R = Bu-n (1), Ph (2), Th (3)] and [Pt(TeR)(R)(dppn)] [R = Ph (4), Th (5)] as a result of the cleavage of the Te-Te or C-Te bond, respectively. The reactions and the product distributions were monitored by P-31{H-1} NMR spectroscopy. The spectral interpretation was assisted by the high-yield preparation of [Pt(TePh)(2)(dppn)] (2) and [Pt(TeTh)(2)(dppn)] (3) by ligand exchange reactions from [PtCl2(dppn)], and by the crystal structure determinations and spectral characterizations of 2 and 3. Two series of reactions were carried out both at room temperature and at -80 degrees C. One involved the addition of the toluene solution of R2Te2 to that of [Pt(eta(2)-nb)(dppn)], and the other the addition of [Pt(eta(2)-nb)( dppn)] solution to the R2Te2 solution. The oxidative addition of (Bu2Te2)-Bu-n to [Pt(eta(2)-nb)(dppn)] yielded solely [Pt((TeBu)-Bu-n)(2)(dppn)]. In case of Ph2Te2 and Th2Te2, the reaction of equimolar amounts of ditelluride and [Pt(eta(2)-nb)(dppn)] afforded only [Pt(TeR)(R)(dppn)] (R = Ph, Th), but when an excess of R2Te2 was used, the addition of [Pt(eta(2)-nb)(dppn)] to the ditelluride resulted in the formation of a mixture of [Pt(TeR)(2)(dppn)] and [Pt(TeR)(R)(dppn)] with the latter the main component. An excess of R2Te2 and the lowering of the temperature favoured the formation of [Pt(TeR) 2(dppn)]. The reaction energetics in toluene was calculated at revPBE/TZVP(f) level of theory. The increase of the electron withdrawing nature of the organic substituent rendered [Pt(TeR)(R)(dppn)] increasingly stable with respect to [Pt(TeR)(2)(dppn)]. The computation of the energy profiles of the likely pathways of the oxidative addition indicated that concurrent formation of [Pt(TeR)(2)(dppn)] and [Pt(TeR)(R)(dppn)] (R = Ph, Th) may be more likely than the formation of the latter due to the decomposition of the former. This was verified experimentally by stirring pure [Pt(TeR)(2)(dppn)] in toluene for a prolonged time at room temperature. No decomposition was observed. (C) 2017 Elsevier B.V. All rights reserved.