Iron, Rhodium and Iridium catalysts with N,N- and P,N-donor ligands for amine and alcohol synthesis

Abstract

This thesis describes investigations into the metal complex catalysed synthesis of amines and alcohols. Chiral rhodium and iridium complexes were synthesised and used as catalysts for the asymmetric hydrogenation of imines and hydroamination of alkenes. Iron species were employed as catalysts for the hydrosilation of imines and ketones. A series of chiral rhodium(I) and iridium(I) metal complexes containing N,N- and P,N-donor ligands were synthesised (2.1-2.5, 2.11-2.14, 2.17-2.28, 2.31-2.42). The core structures of these ligands were based upon bis(pyrazol-1-yl)methane (Bpm) and 1-(2-{diphenylphosphino}ethyl)pyrazole (PyP), with chiral modifications using camphor (CamBpm and CamPyP) and menthone (MenthBpm and MenthPyP) motifs. The synthesised complexes were used as catalysts for the asymmetric hydrogenation of imines and the asymmetric hydroamination of aminoalkenes. Conversions of up to 98 and 96 % were achieved respectively. Asymmetric induction was observed in the hydrogenation of N-(1-phenylethylidene)aniline (2.50) with up to 32% ee detected using chiral capillary electrophoresis. A series of iron(II) complexes of the general formulae [Fe(DmBpm)(X)2] (where DmBpm = bis(3,5-dimethylpyrazol-1-yl)methane, X = Cl (3.12), Br (3.15) and SCN (3.17)), [Fe(PyP)(X)2] (where X = Cl (3.13) and Br (3.16)) and [Fe(PyP)X(SCN)2] (where x = 1 (3.18), 2 (3.19)), and the metal complex [Fe(Bpm)2Br2] (3.14) were synthesised. The solid state structures of these compounds as well as the dimer [Fe(μ-Cl)(Bpm)2]22[BPh4] (3.20) were obtained using X-ray diffraction. The diamagnetic complex (3.19) and paramagnetic complex (3.18) were found to interconvert in dichloromethane. The hydrosilation of acetophenone was catalysed by both preformed iron complexes and those formed in situ from the combination of iron metal precursors (FeCl2, FeBr2, Fe(OAc)2, [Fe(CH3CN)6]2[AlCl4] and Fe3(CO)12) and ligands (Bpm, DmBpm, PyP and DmPyP (1-(2-{diphenylphosphino}ethyl)3,5-dimethylpyrazole)). The combination of Fe(OAc)2 and DmBpm was the most efficient catalyst system, which depended upon the silane used and the ratio of metal to ligand. A Hammet plot was constructed furthering our understanding of the role of the acetophenone species in the catalytic cycle. The hydrosilation of the imine N-benzylidene-aniline (2.53) was catalysed by iron complexes formed in situ from iron precursors (Fe(OAc)2 and Fe3(CO)12) and ligand (Bpm, DmBpm, PyP and DmPyP) combinations.