Synthesis, structures and studies of organoiron compounds

Abstract

An A value of 3.7 kcal/mole was determined for the (η⁵-cyclopentadienyl) iron (II) dicarbonyl group by variable temperature ¹H NMR spectroscopic studies on cis-4-phenyl-1-(η⁵-cyclopentadienyl) iron (II) dicarbonyl cyclohexane. This is the first determination of the A value of a group with a transition metal directly attached to a cyclohexane ring. The energy of activation (-ΔG‡) for ring inversion of cis-4-phenyl-1-(η⁵-cyclopentadienyl) iron (II) dicarbonyl cyclohexane was calculated to be 9.4 kcal/mol. The stereospecific synthesis of cis- and trans-4-phenyl-1-(η⁵-cyclopentadienyl) iron (II) dicarbonyl cyclohexane, cis- and trans-4-tert-butyl-1-(η⁵-cyclopentadienyl) iron (II) dicarbonyl cyclohexane and the X-ray crystal structure of cis-4-tert-butyl-1-(η⁵-cyclopentadienyl) iron (II) dicarbonyl cyclohexane are reported. The multistep stereospecific synthesis of the redox active adenine analog (S)-ferrocenyl-4-aminopyrimidine is reported. This redox active system will be incorporated into oligonucleotides to study the electron transfer through the molecular π-stack system of DNA in future studies. This synthesis used a chiral metalation to synthesize α-aminoferrocenenitrile. t-Butylcarbamate as the metalation-directing group gave a low yield of the 1,2-disubstituted ferrocene. N,N-diisopropylcarboxamide as the metalation-directing group using a chiral base gave moderate yields of 1,2-disubstituted ferrocene derivatives. However, standard hydrolytic methods failed to hydrolyze the diisopropylamide grouping in these 1,2-disubstituted ferrocene derivatives. A new method was developed to convert the amide functionality of N,N-diisopropylferrocenecarboxamide to ester functionality using Me₃O⁺BF₄⁻, NaOMe and an acidic workup. Unfortunately, when this condition was applied to iodo-N,N-diisopropylferrocenecarboxamide and amino-N,N-diisopropylferrocenecarboxamide, only starting materials and N',N'-dimethylamino-N,N-diisopropylferrocenecarboxamide were obtained, respectively. A chiral acetal as the metalation-directing group was used to give stereoselectively (S)-α-carbomethoxyferrocenecarboxaldehyde after the hydrolysis of the acetal group. The aldehyde was then converted to the nitrile, and the ester group was converted to an amino group to give (S)-α-aminoferrocenenitrile. In a two step sequence, (S)-α-aminoferrocenenitrile was reacted with HC(OMe)₃ and gaseous ammonia to give (S)-α-ferrocenyl-4-aminopyrimidine.