14841-07-7Relevant articles and documents
Synthesis, substitution, and isomerization reactions of trans-Re(CO)4LX (L = group 15 donor ligands; X = Br, I)
Ingham, Wayne L.,Coville, Nell J.
, p. 2551 - 2558 (2008/10/08)
The cleavage of Re2(CO)8L2 with X2 (X = I, L = PPh3, P(OMe)Ph2, P(OMe)3, P(OMe)2Ph, PMePh2, PMe2Ph, P(OPh)3, P(O-o-tol)3, P(OiPr)3, P(CH2C6H5)3; X = Br, L = PPh3, P(OMe)3, P(OMe)2Ph, PMe2Ph, P(OPh)3, P(CH2C6H5)3) in CH2Cl2 gives trans-Re(CO)4LX in yields between 20% and 50% as well as cis-Re(CO)4LX (>50%). Reactions of Re2(CO)9L with Br2, by contrast, gave only cis-Re(CO)4LBr and Re(CO)5Br, while reactions of Re2(CO)9PBz3 (Bz = CH2C6H5) with I2 gave Re(CO)5I as well as a mixture of cis- and trans-Re(CO)4PBz3I (ratio 72:28). The PBz3-containing product ratio could be modified by addition of I-(35:65 isomer ratio) and Br- (15:85, cis-trans ratio; product contained mixture of Re(CO)4PBz3I and Re(CO)4PBz3Br). The data for the cleavage reactions of Re2(CO)10-nLn (n = 1, 2) can be explained by an electrophilic attack of halogen, followed by two competing pathways (concerted, associative) involving attack of the nucleophile. It is predicted that in the total product spectrum (Re(CO)5X, Re(CO)4LX) that a maximum of 50% trans-Re(CO)4LX can be obtained by the halogen cleavage route. An IR kinetic investigation of the trans- to cis-Re(CO)4LX isomerization reaction is consistent with an intramolecular rearrangement process that is influenced by the halide (I 3 3 ～ P(OPh)3 ～ PMe2Ph 2 ～ PPh3 iPr)3 3). Reaction of trans-Re(CO)4PBz3I with L (L = P(OPh)3, t-BuNC) at 100°C in C6D6 revealed that isomerization (60%) was more rapid than substitution (3NO/CH3CN or PdO/t-BuNC gave product ratios of cis-and trans-Re(CO)3(PBz3)LI (L = CH3CN, t-BuNC) that were consistent with substitution preceding isomerization. The Re-CO bonds in trans-Re(CO)4PBz3I are less prone to cleavage than equivalent cis Re-CO bonds in cis-Re(CO)4PBz3I.
Comparison of the thermal and photochemical reactions of (η1-cyclopentadienyl)Re(CO)5 and (η1-9-fluorenyl)Re(CO)5: Nonthermal chemical reactions from the lowest excited state
Young, Kent M.,Miller, Timothy M.,Wrighton, Mark S.
, p. 1529 - 1537 (2007/10/02)
Near-UV (366 nm) irradiation of the new complexes (η1-R)Re(CO)5 (R = C5H5, 9-fluorenyl) in alkane 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 (η-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. The ultimate radical products are Re2(CO)10 and C10H10 in the absence of radical traps. Only Re-R cleavage is observed for (η1-9-fluorenyl)Re(CO)5 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 ΔH ? of 28.3 ± 1 kcal mol-1 and ΔS? of 7 ± 3 cal mol-1 K-1. (η5-Fluorenyl)Re(CO)3 reacts at 295 K with CO to quantitatively regenerate (η1-9-fluorenyl)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 (ΔH? = 25.2 ± 1.6 kcal mol-1 and ΔS? = 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)5 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-fluorenyl)Re(CO)5 have been established spectroscopically and by chemical trapping experiments.
