Synthesis, structures and rac/meso isomerization behaviour of bisplanar chiral bis(phosphino-η 5-indenyl)iron(II) complexes

Abstract

Syntheses of the phosphinoindenes 1-(diphenylphosphino)-3-methylindene ( 1b), 3-(diphenylphosphino)-2-methylindene ( 1c), 1-(diphenylphosphino)-2,3-dimethylindene ( 1d), 4,7-dimethyl-3-(diphenylphosphino)indene ( 1e), 1-(diphenylphosphino)-3,4,7-trimethylindene ( 1f) and 3-(diisopropylphosphino)indene ( 1i) were carried out by treatment of the appropriate indenide with the appropriate chlorophosphine. The silylphosphinoindene 3-(diphenylphosphino)-1-(trimethylsilyl)indene ( 1h) was prepared by treatment of the indenide of 3-(diphenylphosphino)indene ( 1a) with trimethylsilylchloride. These indenes, in addition to 1a, were then used, after deprotonation with BuLi, to prepare the corresponding indenyl ferrocenes, 2a– 2e, 2h and 2i, by treatment with ferrous chloride in a 2:1 ratio. These compounds were characterized by 1H, 13C, and 31P NMR spectroscopy, as well as by mass spectrometry, except for the highly-sensitive diisopropylphosphine 2i that could only be characterized by 31P NMR spectroscopy. All of these ferrocene complexes are bisplanar chiral systems that can potentially form rac and meso isomers. In all cases both isomers were observed but for 2b and 2h only one could be isolated. The rac isomers of complexes 2a, 2b, 2d, and 2e, as well as the meso isomer of 2e, were studied by X-ray crystallography. Only complexes 2a and 2i were observed to undergo rac/meso isomerization processes at ambient temperature in THF solvent. We were unable to prepare the sterically congested hexamethylferrocene 2f. Generally, it was found that increasing substitution on the indenyl ring increases the reactivity and sensitivity of the ferrocene.