Datensatz

Zusammenfassung

Continued irradiation of W(CO)₆ in the presence of excess bis(trimethylsilyl)ethyne (btmse) in n-hexane solution yields W(CO)₅(η²-btmse) as the sole product, with quantum yields of 0.66 and 0.69 at λ_exc = 365 and 313 nm, respectively. Cr(CO)₆ behaves analogously, while with Mo(CO)₆ the initially generated Mo(CO)₅(η²-btmse) undergoes further CO substitution to form trans-Mo(CO)₄(η²-btmse)₂ as the second product. All four compounds were isolated in crystalline form and fully characterized by elemental analysis, MS, IR, and NMR spectroscopies as well as by single-crystal X-ray crystallography. They assume a quasi-octahedral coordination geometry with the alkyne triple bond being eclipsed to one OC−M−CO axis and, in the case of trans-Mo(CO)₄(η²-btmse)₂, in trans-orthogonal orientation to the second alkyne. Both Mo(CO)₅(η²-btmse) and Cr(CO)₅(η²-btmse) are labile toward alkyne displacement by CO, whereas W(CO)₅(η²-btmse) and trans-Mo(CO)₄(η²-btmse)₂ undergo spontaneous ¹²CO/¹³CO exchange in the dark under mild conditions. Partially ¹³CO labeled samples generated in this way provide complementary CO stretching vibrational data needed for thorough analyses at the level of the energy-factored CO force field approximation. From all the structural features and spectroscopic data it is evident that bis(trimethylsilyl)ethyne acts as a two-electron donor ligand in this series of d⁶ carbonylmetal(0) complexes.