TY - JOUR
T1 - Comparison of the Thermal and Photochemical Reactions of (η1-Cyclopentadienyl)Re(CO)5 and (η1-9-Fluorenyl)Re(CO)5
T2 - Nonthermal Chemical Reactions from the Lowest Excited State
AU - Young, Kent M.
AU - Miller, Timothy M.
AU - Wrighton, Mark S.
PY - 1990/1
Y1 - 1990/1
N2 - Near-UV (366 nm) irradiation of the new complexes (η1-R)Re(CO)5 (R = C5H5, 9-fluorenyl) inalkane solution at 295 K yields predominantly radical products, whereas thermolysis yields only the fully ring-slipped (η5-R)Re(CO)3 species. Irradiation at 366 nm of (η1-C5H5)Re(CO)5 in deoxygenated alkane solutions at 295 K yields some CO loss to give (η5- C5H5)Re(CO)3, Φ = 0.007 ± 0.002, and mainly Re-R bond cleavage giving Re(CO)5 and R radicals with Φ = 0.06 ± 0.02. Theultimate radical products are Re2(CO)10 and C10H10 in the absence of radical traps. Only Re-R cleavage isobserved for (η1-9-fluorenyl)Re(CO)s upon irradiation at 366 nm with Φ = 0.04 ± 0.004 in deoxygenated alkane to give Re2(CO)10 and 9,9'-bifluorene. Thermolysis of (η1-R)Re(CO)5 (R = C5H5,9-fluorenyl) leads to quantitative conversion to the fully ring-slipped products, (η5-C5H5)Re(CO)3 or (η5-fluorenyl)Re(CO)3, respectively. Thermal ring slippage of (η1-9-fluorenyl)Re(CO)5 to (η5-fluorenyl)Re(CO)3 is reversible and occurs with a rate of ~ 1 × 10-3 s-1 at 400 K. The rate of ring slippage is suppressed by a factor of > 100 under 1 atm of CO. In the presence of 0.05 M PPh3, (η1-9-fluorenyl)Re(CO)4PPh3 is the exclusive thermolysis product and forms with ∆H* of 28.3 ± 1 kcal mol-1 and 5* of 7 ± 3 cal mol-1 K-1. (η5-Fluorenyl)Re(CO)3 reacts at 295 K with CO to quantitatively regenerate (η1-9-fiuorenyl)Re(CO)5 with a rate of 9.7 × 10-5 s-1 under 1 atm of CO. The rate of thermal ring slippage of (η1-C5H5)Re(CO)5 to (η5-C5H5)Re(CO)3 is 4.2 × 10-4 s-1 at 325 K (&H* = 25.2 ± 1.6 kcal mol-1 and &S* = 7 ± 3 cal mol-1 K-1) and is not affected by 1 atm of CO. The rate of thermal ring slippage is decreased by ~60% at 295 K by 1200 psig CO. (η5-C5H5)Re(CO)3 does not react with up to 1200 psig of CO at 295 K. Optical and photochemical measurements on CH3Re(CO)5 show lowest excited state behavior consistent with results for the η1-C5H5 and η1-9-fluorenyl species. The thermal behavior of CH3Re(CO)5 (qualitatively slower reactions) is in accord with the conclusion that CO loss from η1-C5H5 and η1-9-fluorenyl species is assisted by the unsaturated hydrocarbon ligand. Irradiation at 254 or 366 nm of (η1-C5H5)Re(CO)5 in alkane glasses at 95 K leads to CO loss as the only detectable photoprocess: the ring-slipped (η3- C5H5)Re(CO)4 and (η5-C5H5)Re(CO)3 are formed. Irradiation at 254 nm of (η1-9-fluorenyl)Re(CO)5 under the same conditions leads to the formation of (η3-fluorenyl)Re(CO)4 and a new, isomeric (fluorenyl)Re(CO)s product, but 366-nm irradiation yields predominantly (>90%) isomerization, not CO loss. The identities of the η3 intermediates from (η1-C5H5)Re(CO)5 and (η1-9-nuorenyl)Re(CO)5 have been established spectroscopically and by chemical trapping experiments.
AB - Near-UV (366 nm) irradiation of the new complexes (η1-R)Re(CO)5 (R = C5H5, 9-fluorenyl) inalkane solution at 295 K yields predominantly radical products, whereas thermolysis yields only the fully ring-slipped (η5-R)Re(CO)3 species. Irradiation at 366 nm of (η1-C5H5)Re(CO)5 in deoxygenated alkane solutions at 295 K yields some CO loss to give (η5- C5H5)Re(CO)3, Φ = 0.007 ± 0.002, and mainly Re-R bond cleavage giving Re(CO)5 and R radicals with Φ = 0.06 ± 0.02. Theultimate radical products are Re2(CO)10 and C10H10 in the absence of radical traps. Only Re-R cleavage isobserved for (η1-9-fluorenyl)Re(CO)s upon irradiation at 366 nm with Φ = 0.04 ± 0.004 in deoxygenated alkane to give Re2(CO)10 and 9,9'-bifluorene. Thermolysis of (η1-R)Re(CO)5 (R = C5H5,9-fluorenyl) leads to quantitative conversion to the fully ring-slipped products, (η5-C5H5)Re(CO)3 or (η5-fluorenyl)Re(CO)3, respectively. Thermal ring slippage of (η1-9-fluorenyl)Re(CO)5 to (η5-fluorenyl)Re(CO)3 is reversible and occurs with a rate of ~ 1 × 10-3 s-1 at 400 K. The rate of ring slippage is suppressed by a factor of > 100 under 1 atm of CO. In the presence of 0.05 M PPh3, (η1-9-fluorenyl)Re(CO)4PPh3 is the exclusive thermolysis product and forms with ∆H* of 28.3 ± 1 kcal mol-1 and 5* of 7 ± 3 cal mol-1 K-1. (η5-Fluorenyl)Re(CO)3 reacts at 295 K with CO to quantitatively regenerate (η1-9-fiuorenyl)Re(CO)5 with a rate of 9.7 × 10-5 s-1 under 1 atm of CO. The rate of thermal ring slippage of (η1-C5H5)Re(CO)5 to (η5-C5H5)Re(CO)3 is 4.2 × 10-4 s-1 at 325 K (&H* = 25.2 ± 1.6 kcal mol-1 and &S* = 7 ± 3 cal mol-1 K-1) and is not affected by 1 atm of CO. The rate of thermal ring slippage is decreased by ~60% at 295 K by 1200 psig CO. (η5-C5H5)Re(CO)3 does not react with up to 1200 psig of CO at 295 K. Optical and photochemical measurements on CH3Re(CO)5 show lowest excited state behavior consistent with results for the η1-C5H5 and η1-9-fluorenyl species. The thermal behavior of CH3Re(CO)5 (qualitatively slower reactions) is in accord with the conclusion that CO loss from η1-C5H5 and η1-9-fluorenyl species is assisted by the unsaturated hydrocarbon ligand. Irradiation at 254 or 366 nm of (η1-C5H5)Re(CO)5 in alkane glasses at 95 K leads to CO loss as the only detectable photoprocess: the ring-slipped (η3- C5H5)Re(CO)4 and (η5-C5H5)Re(CO)3 are formed. Irradiation at 254 nm of (η1-9-fluorenyl)Re(CO)5 under the same conditions leads to the formation of (η3-fluorenyl)Re(CO)4 and a new, isomeric (fluorenyl)Re(CO)s product, but 366-nm irradiation yields predominantly (>90%) isomerization, not CO loss. The identities of the η3 intermediates from (η1-C5H5)Re(CO)5 and (η1-9-nuorenyl)Re(CO)5 have been established spectroscopically and by chemical trapping experiments.
UR - https://www.scopus.com/pages/publications/0011636581
U2 - 10.1021/ja00160a036
DO - 10.1021/ja00160a036
M3 - Article
AN - SCOPUS:0011636581
SN - 0002-7863
VL - 112
SP - 1529
EP - 1537
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 4
ER -