Bis(trimethylsilyl)ethyne as a two-electron alkyne ligand in group 6 carbonylmetal(0) complexes: Photochemical syntheses and comprehensive 2 characterization of M(CO)(5)(eta(Me3SiC)-Me-2=CSiMe3) (M = W, Mo, Cr) and trans-Mo(CO)(4)(eta(2)-Me3SiC=CSiMe3)(2)

Continued irradiation of W(CO)(6) in the presence of excess bis(trimethylsilyl)ethyne (btmse) in n-hexane solution yields W(CO)(5)(eta(2)-btmse) as the sole product, with quantum yields of 0.66 and 0.69 at lambda(exc) = 365 and 313 nm, respectively. Cr(CO)(6) behaves analogously, while with MO(CO)(6) the initially generated Mo(CO)(5)(eta(2)-btmse) undergoes further CO substitution to form trans-Mo(CO)(4)(eta(2)-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)(eta(2)-btmse)(2), in trans-orthogonal orientation to the second alkyne. Both Mo(CO)(5)(eta(2)-btmse) and Cr(CO)(5)(eta(2)-btmse) are labile toward alkyne displacement by CO, whereas W(CO)(5)(eta(2)-btmse) and trans-MO(CO)(4)(eta(2)-btmse)(2) undergo spontaneous (CO)-C-12/(CO)-C-13 exchange in the dark under mild conditions. Partially (CO)-C-13 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 d(6) carbonylmetal(0) complexes

PHOTOINDUCED REACTIONS OF CR(CO)3-COORDINATED 1,3,5-CYCLOHEPTATRIENE - (6+2) CYCLOADDITION WITH AN ALKYNE AND CATALYTIC 1,6-HYDROGENATION

Irradiation of Cr(CO)3(eta(6)-1,3,5-cycloheptatriene) (1) in the presence of bis(trimethylsilyl)ethyne results in [6 + 2] cycloaddition of the alkyne to the cycloheptatriene ligand, yielding Cr(CO)3{eta(4:2)-7,8-bis(trimethylsilyl)bicyclo[4.2.1]nona-2,4,7-triene} (2, 60% yield, PHI = 0.08), which upon oxidative decomposition with Ce(IV) releases the organic cycloadduct, 7,8-bis-(trimethylsilyl)bicyclo[4.2.1]-nona-2,4,7-triene (3). Photocatalytic hydrogenation of 1,3,5-cycloheptatriene in the presence of complex 1 affords 1,3-cycloheptadiene. This process involves 1,6-addition of hydrogen, as demonstrated by using D2

Efficient electron transfer across hydrogen bond interfaces by proton-coupled and -uncoupled pathways

Thermal electron transfer across hydrogen bond remains largely unexplored. Here the authors demonstrate that electron self-exchange through hydrogen bonds is highly efficient and can proceed either via the known proton-coupled pathway or an overlooked proton-uncoupled pathwa