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((kappa)^2-H2CH2PNO)Br] (4) and [Re(CO)3((kappa)^2-PPh3oxazBr)] (5), fully characterized by 1H and 31P NMR spectroscopy and Xray 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-(2diphenylphosphinophenyl)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.