Synthesis and Structural Characterization of Novel Re(I) Tricarbonyl Complexes Anchored on a Phosphinoarylbenzylamine and a Phosphinoaryloxazoline Generated in Situ

Reduction of the amide or replacement of the hydroxyl by a bromide in 2-(diphenylphosphanyl)-N-(2-hydroxyethyl)benzamide (H2PNO) yielded the compounds 2-(diphenylphosphanyl)-N-(2-hydroxyethyl)benzylamine (H2CH2PNO,
1) and N-(2-bromoethyl)-2-(diphenylphosphanyl)benzamide (HPNBr, 2), respectively. Compound 2 is obtained in
low yield and, depending on the reaction conditions, is mixed with starting material or with a product which has
been identified as 2-(2-diphenylphosphinophenyl)oxazoline (PPh3oxaz, 3). Compounds 1 and 2 react with
(NEt4)2[ReBr3(CO)3], leading to the complexes [Re(CO)3(κ2-H2CH2PNO)Br] (4) and [Re(CO)3(κ2-PPh3oxazBr)] (5),
fully characterized by 1H and 31P NMR spectroscopy and X-ray crystallographic analysis. Complex 5 is the first
example of a Re(I) tricarbonyl anchored on a phosphorus−oxazoline ligand, which has been generated during the
course of complex formation. In the unexpected and unusual complex 5, the Re atom is stabilized by a bidentate
2-(2-diphenylphosphinophenyl)oxazoline, by a bromide, and by three facially arranged carbonyl groups. In complex
4, the carbonyl groups are also facially coordinated to the metal center and the other three remaining coordination
positions are occupied by a bromide and by the bidentate (P, N) ligand 2-(diphenylphosphanyl)-N-(2-hydroxyethyl)benzylamine.