Stereocontrol of Metal-Centred Chirality in Rhodium(III) and Ruthenium(II) Complexes with N 2 N'P Ligand.

Rh(III) and Ru(II) complexes, [RhCl 2 (κ 4 -N 2 N'P-L)][SbF 6 ] (1) and [RuCl 2 (κ 4 -N 2 N'P-L)] (2), were synthesised using the tetradentate ligand L (L=N,N-bis[(pyridin-2-yl)methyl]-[2-(diphenylphosphino)phenyl]methanamine). In each case only one diastereomer is detected, featuring cis-disposed pyridine groups. The chloride ligand trans to pyridine can be selectively abstracted by AgSbF 6 , with the ruthenium complex (2) reacting more readily at room temperature compared to the rhodium complex (1) which requires elevated temperatures. Rhodium complexes avoid the second chloride abstraction, whereas ruthenium complexes can form the chiral bisacetonitrile complex [Ru(κ 4 -N 2 N'P-L)(NCMe) 2 ][SbF 6 ] 2 (5) upon corresponding treatment with AgSbF 6 . The complex [RhCl 2 (κ 4 -N 2 N'P-L)][SbF 6 ] (1) has also been used to synthesise polymetallic species, such as the tetrametallic complex [{RhCl 2 (κ 4 -N 2 N'P-L)} 2 (μ-Ag) 2 ][SbF 6 ] 4 (6) which was formed with complete diastereoselectivity and chiral molecular self-recognition. In addition, a stable bimetallic mixed-valence complex [{Rh(κ 4 -N 2 N'P-L)}{Rh(COD)}(μ-Cl) 2 ][SbF 6 ] 2 (7) (COD=cyclooctadiene) was synthesised. These results highlight the significant differences in chloride lability between Rh 3+ and Ru 2+ complexes and demonstrate the potential for complexes to act as catalyst precursors and ligands in further chemistry applications.