A new organometallic photoreaction: interconversion of metal-alkylidene geometric isomers
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Benzylidene complex [(η-C5H5)Re(NO)-(PPh3)(=CHC6H5)]+PF6−(1), which exists as a >99:1 mixture of anticlinal (1t, “thermodynamic”) and synclinal (1k, “kinetic”) Re=C bond geometric isomers at room temperature, is isomerized when irradiated between −20 and −78 °C in CD2Cl2, CD3CN, or (CD3)2CO to a (55 ± 3):(45 ± 3) 1t/1k photostationary state. Propylidene[(η-C5H5)Re(NO)(PPh3)(=CHCH2CH3)]+PF6− (2), which exists as a (95±1):(5±1) mixture of anticlinal (2t) and synclinal (2k) isomers at room temperature, is similarly isomerized to a (59 ± 2):(41 ± 2) photostationary state. Absorption spectra of 1t and 2t and unsuccessful attempts to photosensitize 1t → 1k (azulene, rose bengal, eosin Y) are reported. Thermal isomerization rates for 1k → 1t, measured between 4 °C (t1/2 = 443 min) and 29.5 °C (t1/2 = 17 min), yield ΔH⧧ = 20.9 ± 0.4 kcal/mol and ΔS⧧ = −3.8 ± 0.2 eu. The benzylidene complex [(η-C5H5)Fe(CO)(PPh3)(=CHC6H5)]+CF3CO2− (3) decomposes upon low-temperature irradiation. © 1982, American Chemical Society. All rights reserved.
author list (cited authors)
McCormick, F. B., Kiel, W. A., & Gladysz, J. A.