Diastereoselective Synthesis of Arene Ruthenium(II) Complexes Containing Chiral Phosphetane-Based Tethers † ,1

• Published in: Organometallics 2006-05, Vol.25 (10), p.2607-2616
• Main Authors: Pinto, Patrícia, Götz, Andreas W, Marconi, Guido, Hess, Bernd A, Marinetti, Angela, Heinemann, Frank W, Zenneck, Ulrich
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om050461z

Enantiomerically pure cyclic (R,R)-sulfates have been transformed into novel enantiopure ligands of the general type (S,S)-2,4-R2-1-(3-phenylpropyl)phosphetane (7a−c; R = Cy, i-Pr, t-Bu). 7a−c split the arene ruthenium complex dimer [{RuCl2(η6-C6H5COOMe)}2] (8) by forming the mononuclear σ complexes (S C,S C)-[RuCl2(η6-C6H5COOMe){2,4-R2-1-(3-phenylpropyl)-η1-phosphetane}] (9a−c). An intramolecular arene ligand displacement reaction leads to (S C,S C)-[RuCl2{2,4-R2-1-(η6-3-phenylpropyl)-η1-phosphetane}] (10a−c) with tethered side chains of the arene ligand. Nucleophilic substitution of a chloride ligand by aniline with the assistance of NaPF6 gives access to the diastereomeric complex salts (S C,S C)-[RuCl(aniline){2,4-R2-1-(η6-3-phenylpropyl)-η1-phosphetane}] (11a−c). Good diastereoselectivities were obtained with de values between 84 and 88%. The absolute structures of the major diastereomers of 11a−c have been determined by X-ray structure analysis. R Ru,S C,S C configurations were found in all cases. DFT calculations performed on the dechlorinated 16-valence-electron intermediate cation (S C,S C)-[RuCl{2,4-di-tert-butyl-1-(η6-3-phenylpropyl)-η1-phosphetane}]+ ([12]+) are in favor of an attack of aniline from the pro-R Ru side of the complex. Investigation of the relative stabilities of the R Ru and S Ru diastereomers of the complex cation [11c]+ revealed an almost isoenergetic situation. The diastereoselectivity of the ligand exchange reaction is therefore believed to be kinetically controlled.