SYNTHESIS AND CHARACTERIZATION OF CHIRAL RHENIUM SIGMA-KETONE COMPLEXES - BINDING-PROPERTIES OF SYMMETRICAL KETONES AND ALKYLCYCLOHEXANONES

Reactions of the dichloromethane complex [Re(eta-5-C5H5)(NO)(PPh3)(ClCH2Cl)]BF4 1 with cyclohexanone (a), cyclobutanone (b), diphenylcyclopropenone (c), and tropone (d) give the symmetrical sigma-ketone complexes [Re(eta-5-C5H5)(NO)(PPh3)(sigma-O = CR2)]BF4 7a-7d in 50-85% yields after work-up. Similar reactions of 1 with pentan-3-one (e) and 2,4-dimethylpentan-3-one (f) give the analogous ketone complexes 7e and 7f in good spectroscopic yields, but low isolated yields. However, 7e can be isolated in 66% yield from the reaction of the chlorobenzene complex [Re(eta-5-C5H5)(NO)(PPh3)(ClC6H5)]BF4 and pentan-3-one. Reactions of 1 with 3-methylcyclohexanone (h) and trans-1-decalone (j) give complexes 7h and 7j as mixtures of Re/C configurational diastereomers (40-71%). Under most conditions, the symmetrical ketone complexes 7a-7e exhibit a single set of H-1 and C-13 NMR resonances for the C = O substituents that are Z and E to the rhenium. Low-temperature H-1 NMR experiments show that the Z/E ethyl groups in 7e exchange with DELTA-G151-double-ended dagger K = 7.0 kcal mol-1.