Diphenylditellurium Binuclear Complexes with Chromium and Tungsten Pentacarbonyls: Synthesis, Molecular Structure, and Thermal Decomposition

Photochemical reactions of M(CO)₆ (where M is W or Cr) and Ph₂Te₂ taken in a 2 : 1 molar ratio in tetrahydrofuran at room temperature, or reactions of (CO)₅M(thf) with Ph₂Te₂ yield dark lilac binuclear complexes [(CO)₅M]₂(μ-Te₂Ph₂), where M=Cr (3) or M=W (4). The reaction of (CO)₅Cr(Te₂Ph₂) with (CO)₅W(thf) yields the heterometal complex (CO)₅Cr(μ-Te₂Ph₂)W(CO)₅ (5). The structure of 3-5 is determined by X-ray crystallography. The Te-Te bond (up to 2.812(2), 2.808(2), and 2.828(2) Å, respectively) becomes significantly longer upon formation of shortened M-Te bonds in 3 and 4 (2.656(3) and 2.779(2) Å, respectively). A study of thermal decomposition of 3-5 in comparison with mononuclear complexes (CO)₅M(Te₂Ph₂), where M is Cr or W (1 or 2, respectively), proved the exothermicity of consecutive elimination of carbonyl and phenyl groups (at 145-170 and 177-234°C, respectively), to give tellurides MTe as the final products (intermediate ditellurides MTe₂ formed from mononuclear complexes 1 and 2 eliminate one tellurium atom at 268 and 242°C, respectively).