Synthesis and chemistry of 1-acetyl, 2-methylsubstituted cyclopentadienyl thallium and its chiral manganese and rhodium carbonyl derivatives. The molecular structure of [1-CH 3CO, 2-CH 3C 5H 3]Rh(CO)[P(C 6H 5) 3

Abstract

Reaction of sodium methylcyclopentadienide and ethyl acetate yields a 1:1 mixture of the sodium salts of 1-acetyl, 2-methylcyclopentadienide, 1, and its 1-acetyl, 3-methyl isomer, 2. Reaction of this mixture with thallium ethoxide yields the corresponding thallium salts from which pure 1-acetyl, 2-methylcyclopentadienyl thallium, 3, can be obtained by fractional crystallization from ethanol. Isomerically enriched samples of 1-acetyl, 3-methyl thallium compound, 4, can be obtained from the recrystallization filtrates. Reaction of 3 with BrMn(CO) 5 yields the planar chiral complex 1-acetyl, 2-methylcymantrene, 5, as a racemic mixture. Reaction of 3 with [ClRh(CO) 2] 2 gave 1-acetyl, 2-methylcyclopentadienyl rhodium dicarbonyl, 6. Reaction of thallium mixtures enriched in 4 with [ClRh(CO) 2] 2 yields, after chromatography, small samples of 1-acetyl, 3-methylcyclopentadienyl rhodium dicarbonyl, 10. A small quantity of a dinuclear complex, 7, was obtained from 6 and shown to consist of both the meso and racemic forms of 7. Reaction of 6 with trimethylamine oxide yielded a trinuclear complex, 8, whose spectra and chiral HPLC are fully consistent with the expected distribution of isomers for a triangulo complex with three chiral centers. 6 reacts with triphenylphosphine to give the expected carbonyl, triphenylphosphine derivative, 11, which was crystallographically characterized: C 27H 24O 2PRh, monoclinic, P2 1/ c, a = 9.029(1), b = 11.196(2), c = 23.298(4) Å, β = 91.34, V = 2354.7 Å 3, Z = 4, R( F) = 3.65%. Oxidative addition of iodomethane with 11 gives a diastereomeric mixture of cyclopentadienylrhodium(acetyl)iodo(triphenylphosphine) isomers, 12, in an approximately 1:2 ratio indicating modest chiral induction by the ring substituents of addition at the metal. Chiral HPLC using columns of CHIRALCEL OD are described for several of the racemic mixtures.