97074-01-6Relevant articles and documents
Photochemistry of (alkene)pentacarbonyltungsten(0) complexes in rigid alkane at low temperature: Relative importance of dissociative loss of alkene and carbon monoxide
Pope, Keith R.,Wrighton, Mark S.
, p. 2792 - 2796 (2008/10/08)
UV irradiation (254 or 313 nm) of W(CO)5(alkene) (alkene = C2H4, C3H6, 1-C5H10) in methylcyclohexane at 77 K yields two primary photoprocesses, CO and alkene loss. The relative loss of alkene is approximately 2 times more important upon 313-nm irradiation than when irradiation is at 254 nm. Further, the relative importance of alkene loss increases approximately threefold: C2H4 3H6 5H10. The loss of alkene is accompanied by the formation of W(CO)5, while loss of CO gives the 16e W(CO)4(alkene) species. Since the spectrum of the CO-loss product from W(CO)5(C2H4) is nearly the same as that from W(CO)5(C3H6) or W(CO)5(1-C5H10), no evidence for W(CO)4(H)(π-allyl) complexes is found. Even W(CO)5(η2-1,4-pentadiene) and W(CO)5(η2-cyclopentadiene), having doubly allylic C-H bonds, do not yield a hydride upon light-induced loss of CO. The measurement of the quantitative ratio of alkene:CO loss has been made possible by a quantitative determination of the extinction coefficient, ε, for free CO at 2132 cm-1 in methylcyclohexane at 77 K. The values of εco were determined by measuring the absorptivity at 2132 cm-1 for known fractional light-induced conversion of Cr(CO)6, W(CO)6, and (η5-C5H5)W(CO)3CH3 to CO and the appropriate 16e metal carbonyl; the values of εco from these precursors are 420 ± 40, 390 ± 20, and 420 ± 20 M-1 cm-1, respectively. In a 2-methyltetrahydrofuran glass the value of εco is lower, 350 ± 20 M-1 cm-1.
