CHIRAL CYCLOPENTADIENYL CATALYSTS .3. SYNTHESIS AND REACTIONS OF -(2,3,4,5-TETRAMETHYLCYCLOPENTA-1,3-DIENYL)BENZENE - CRYSTAL-STRUCTURE OF [RH(ETA-5-C5ME4C6H4CH(ME)NME2)CL2]

The synthesis of -(2,3,4,5-tetramethylcyclopenta-1,3-dienyl)benzene (H L) and its reactions with [Ru3(CO)12] and IrCl3.3H2O have been perform ed. Compound HL also reacts with RhCl3.3H2O to give a mixture of [Rh{e ta5-C5Me4C6H4CH(Me)NMe2}Cl2] 1 and [{Rh[eta5-C5Me4C6H4CH(Me)NMe2.HCl]C l2}2] 2. A single-crystal X-ray diffraction study of 1 was carried out : the compound crystallises in the orthorhombic, space group P2(1)2(1) 2(1) (D(2)4, no. 19) with a = 8.691 (6), b = 15.803(15), c = 13.840(10 ) angstrom and Z = 4; R = 0.0657. Interconversion between 1 and 2 can be effected readily using HCl or base respectively. Other aspects of t he chemistry of 1 have been investigated including its conversion into [Rh{eta5-C5Me4C6H4CH(Me)NMe2}(C2H4)2] in which rotation of the co-ord inated ethene molecules has been estimated by H-1 NMR spectroscopy to have a free energy of activation (DELTAG(double dagger)) = 67.2 kJ mol -1. In contrast to 1, the methylated derivative [Rh{eta5-C5Me4C6H4CH(M e)NMe3+BF4-}Cl2] functions as a hydrogenation catalyst but with prochi ral alkenes the optical yields were low (less-than-or-equal-to 8% enan tiomeric excess).