Synthesis and structural characterization of new phosphinooxazoline complexes of iron

The first phosphinooxazoline chelate complexes of iron were synthesized, and their structural and electronic properties were studied. The known phosphinooxazolines 2-(2-(diphenylphosphino)phenyl)-4,5-dihydrooxazole (7a), 2-(2-(diphenylphosphino)phenyl)-4,4-dimethyl-4,5-dihydrooxazole ( 7b), ( S)-4-benzyl-2-(2-(diphenylphosphino) phenyl)-4,5-dihydrooxazole ( 7e) and ( R)-2-(2-(diphenylphosphino)phenyl)-4-phenyl-4,5-dihydrooxazole ( 7f) were synthesized by a modified three step literature procedure with improved 67-60% overall yields. The new electronically tuned phosphinooxazolines 2-(5-bromo-2-(diphenylphosphino) phenyl)-4,4-dimethyl-4,5-dihydrooxazole ( 7c), 3-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-4( diphenylphosphino)-N,N-dimethylaniline (7d) and 2-(2-(diphenylphosphino)-3-(trifluoromethyl)phenyl)-4,4-dimethyl-4,5-dihydrooxazole ( 7g) were synthesized in three to six steps with 59-29% overall yields. Reaction of 7a-f with CpFe(CO)(2)I (110 degrees C, 2 h, toluene) gave the iodide salts of the new iron phosphinooxazoline complexes [ CpFe( CO)(7a-f)](+) in 87-21% yield. The new complexes were characterized by X-ray and the molecular structures confirm the octahedral coordination geometry and the half-sandwich structure about the iron center. The impact of different oxazoline ligands on the steric and electronic properties of their iron complexes was determined by analysis of selected bond lengths, nu(C=O) stretching frequency and the oxidation potentials of the ligands and the iron complexes. (C) 2008 Elsevier B. V. All rights reserved.