Chiral cyclopentadienyl catalysts. Part 3. Synthesis and reactions of (S)-1-(1-dimethylaminoethyl)-2-(2,3,4,5-tetramethylcyclopenta-1,3-dienyl)benzene; crystal structure of [Rh{η5-C5Me4C6H4CH(Me)NMe2}Cl2]

Abstract

The synthesis of (S)-1-(1-dimethylaminoethyl)-2-(2,3,4,5-tetramethylcyclopenta-1,3-dienyl)benzene (HL) and its reactions with [Ru₃(CO)₁₂] and IrCl₃·3H₂O have been performed. Compound HL also reacts with RhCl₃·3H₂O to give a mixture of [Rh{η⁵-C₅Me₄C₆H₄CH(Me)NMe₂}Cl₂]1 and [{Rh[η⁵-C₅Me₄C₆H₄CH(Me)NMe₂·HCl]Cl₂}₂]2. A single-crystal X-ray diffraction study of 1 was carried out: the compound crystallises in the orthorhombic, space group P2₁2₁2₁(D₂⁴, no. 19) with a= 8.691 (6), b= 15.803(15), c= 13.840(10)Å and Z= 4; R= 0.0657. Interconversion between 1 and 2 can be effected readily using HCl or base respectively. Other aspects of the chemistry of 1 have been investigated including its conversion into [Rh{η⁵-C₅Me₄C₆H₄CH(Me)NMe₂}(C₂H₄)₂] in which rotation of the co-ordinated ethene molecules has been estimated by ¹H NMR spectroscopy to have a free energy of activation (ΔG^‡)= 67.2 kJ mol^–1. In contrast to 1, the methylated derivative [Rh{η⁵-C₅Me₄C₆H₄CH(Me)NMe₃⁺ BF₄^–}Cl₂] functions as a hydrogenation catalyst but with prochiral alkenes the optical yields were low (⩽8% enantiomeric excess).