A NEW ORGANO-METALLIC PHOTOREACTION - INTERCONVERSION OF METAL-ALKYLIDENE GEOMETRIC ISOMERS
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abstract
Benzylidene complex [(-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[(-C5H5)Re(NO)(PPh3)(=CHCH2CH3)]+PF6 (2), which exists as a (951):(51) 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 H = 20.9 0.4 kcal/mol and S = 3.8 0.2 eu. The benzylidene complex [(-C5H5)Fe(CO)(PPh3)(=CHC6H5)]+CF3CO2 (3) decomposes upon low-temperature irradiation. 1982, American Chemical Society. All rights reserved.