SYNTHESES AND STRUCTURES OF COMPLEXES OF ALPHA,BETA-UNSATURATED CARBONYL-COMPOUNDS AND THE CHIRAL RHENIUM FRAGMENT [(ETA(5)-C5H5)RE(NO)(PPH3)]+ - DIVERGENT KINETIC AND THERMODYNAMIC O=C/C=C BINDING SELECTIVITIES
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Reactions of the substitution-labile dichloromethane complex [(5-C5H5)Re(NO)(PPh3)-(ClCH2C1)]+BF4- with , -unsaturated aldehydes and ketones are described. Acrolein gives a OC complex, which cleanly isomerizes in the solid state (100 C) to a CC complex. Crotonaldehyde gives both and OC complexes (52:48, CH2Cl2, room temperature), which convert at 80 C to a CC complex. Methyl vinyl ketone gives a OC complex, which is characterized by NMR at 25 C. At room temperature, a CC complex forms. Other acyclic vinyl ketones behave similarly. Cyclopentenone and cyclohexenone give OC complexes that only partially isomerize to CC complexes at 6090 C. The acetylenic ketone 4-phenyl-3-butyn-2-one gives a OC complex at 25 C. At room temperature, a CC complex forms. The crystal structure of a CC complex of trans-4-hexen-3-one is determined. The NMR, configurational, and conformational properties of the preceding complexes, all of which can exist in several isomeric forms, are analyzed in detail. These data show that, with respect to the rhenium fragment [(5-C5H5)Re(NO)(PPh3)]+, the OC groups of , -unsaturated aldehydes and ketones are the kinetically preferred binding sites, but the CC or CC groups are generally the thermodynamically preferred binding sites. 1993, American Chemical Society. All rights reserved.
