The chemistry of enantiopure pyridine bis(oxazoline) iron compounds has been explored. The electronic properties of this ligand class have been evaluated relative to aryl- and alkyl-substituted bis (imino)pyridines using cyclic voltammetry and CO stretching frequencies of iron dicarbonyl compounds. Attempts to prepare a pyridine bis(oxazoline) iron dinitrogen complex by sodium amalgam reduction of the corresponding dichloride precursor yielded a catalytically inactive S = 1 bis (chelate) iron complex. Dialkyl derivatives of the general formula ( RPybox)Fe(CH 2SiMe 3) 2 were prepared either by pyridine displacement from (py) 2Fe(CH 2SiMe 3) 2 or by direct dialkylation of the appropriate iron dichloride. Two examples of the S = 2 complexes were characterized by singlecrystal X-ray diffraction. Each enantiopure Pybox iron dialkyl was evaluated in the catalytic hydrosilylation of various ketones. Efficient turnover was observed at 23 0C with 0.3% of the iron precatalyst using PhSiH 3 as the stoichiometric reductant. For comparison, related bis(oxazoline) iron dialkyl compounds were also evaluated and found to be equally effective at 1.0 mol % iron loadings. While low to modest enantioselectivities were observed with both classes of neutral iron dialkyl compounds, high levels of asymmetric induction were obtained for a hindered acetophenone and a-tetralone upon activation of the iron derivative with B(C 6F 5) 3.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry