Carboxamide substituted tetramethylcyclopentadiene - synthesis, characterisation and its iridium(III) complex catalysed reduction of imines.

The novel dimeric iodo-iridium(III) complex, [Ir(Cp*CONMe ₂ )I ₂ ] ₂ , (Cp*CONMe ₂ = η ⁵ - N,N -2,3,4,5-hexamethylcyclopenta-2,4-diene carboxamide) bearing an amide moiety within the tetramethylcyclopentadiene ring, has been synthesised and characterised. The ligand Cp*CONMe ₂ is synthesised as two regioisomers, however the 2-substituted isomer exists as two distinguishable conformers due to restricted rotation about the amide carbonyl carbon and the ring carbon. The relative acidities of Cp*CONMe ₂ and Cp* are compared by their relative rates of H/D exchange. The iridium complex of N,N -2,3,4,5-hexamethylcyclopenta-2-4-diene carboxamide [IrCp*CONMe ₂ ] and ( R,R )-1,2-diphenyl- N '-tosylethane-1,2-diamine (( R , R )-TsDPEN) has been evaluated in the transfer hydrogenation of imines under acidic conditions - a 5 : 2 molar ratio of formic acid : triethylamine as the hydride source for the transfer hydrogenation of 1-methyl-3,4-dihydroisoquinoline (DHIQ) and its 6,7-dimethoxy derivative in acetonitrile. A decreasing enantiomeric excess with reaction progress is attributed to different kinetic orders for formation of the two product amine enantiomers. The pseudo zero-order formation of the R -amine may be due to a pre-steady-state formation of the less stable form of the diastereomeric catalyst. By contrast, both enantiomeric amines from 1-fluorinated methyl DHIQs as substrates for reduction are formed by pseudo first-order processes.