Nonrigid diastereomers: epimerization at chiral metal centers or chiral ligand conformations?

Induced-fit recognition of DNA by organometallic complexes with dynamic stereogenic centers

“…Here, we elaborate a multifunctional mode of DNA binding for organometallic complexes based on the linking of two {( 6 -arene)RuCl(diamine)} units, with a flexible chain. This introduces stereogenic centers at Ru and N, giving potential for dynamic chiral DNA recognition since epimerization at these centers is expected to be facile (15)(16)(17)(18)(19). Such a recognition mechanism contrasts with ''static'' concepts, such as ''shapematch'' for selective DNA recognition by octahedral metallointercalators (20).…”

Epimerization, diastereoselectivity and hemilability in dicationic chiral ruthenium complexes with bidentate (P∧S) bisphosphine monosulfide ligands

“…We recently reported work with heterobidentate P Ù N [1], P Ù O [2][3][4][5][6], and P Ù S [7][8][9][10] ligands, including successful applications in asymmetric catalysis [1,2,[8][9][10]. The resulting metal complexes containing heterobidentate ligands can exhibit unique reactivity, and improved selectivity with respect to their C 2 -symmetric counterparts, as a result of this asymmetry.…”

“…Our previous work has shown that the epimerization of metal chirality in mono-and dicationic ruthenium halfsandwich complexes is generally a relatively facile process, occurring with a half-life of minutes or hours [3][4][5]16]. However, one study has indicated that the situation with some dicationic variants may be quite different, as no metal epimerization was noted for complexes of the type [Ru(g 6 -cymene)(g 2 -P Ù O)(amine)](SbF 6 ) 2 [6].…”

“…L1 (26 mg, 0.060 mmol) was then added, and the solution was stirred for 1 h, and then passed through a plug of silica gel. The product 2 22H, m), (CH arom ); 6.27 (1H, m, CH g6-arene ),5.63 (1H, d, J = 6.9 Hz, CH g6-arene ), 5.53 (1H, dt, J = 5.5, 1.4 Hz, CH g6-arene ), 4.56 (td, J = 5.5, 2.6 Hz, CH g6-arene ), 4.01 (1H, m, CH 2ethylene ), 3.64 (1H, m, CH 2ethylene ), 3.21 (1H, m, CH cyclohexyl ), 3.19 (1H, m, CH 2ethylene ), 2.95 (2H, m, CH 2ethylene and CH cyclohexyl ), 2.734 (3H, s, N(CH 3 ) 2 ), 2.730 (3H, s, N(CH 3 ) 2 ), 2.20-0.60 (20H, m, CH 2cyclohexyl ). 31 P{ 1 H} NMR (161.9 MHz, (CD 3 ) 2 CO): 56.6 (dd, J P-P = 35.7, 19.7 Hz), 40.8 (dd, J P-P = 19.7, 19.3 Hz), 18.3 (dd, J P-P = 35.7, 19.3 Hz).4.3.2.…”

Stereochemical Nonrigidity of Organometallic Complexes

“…Upon lowering the temperature, isomers can be observed, but it is difficult to tell whether these are the isomers or conformations that are frozen out owing to relatively high barriers to rotation about single bonds. 150 This is a particularly important distinction to be made when diastereomers are being used for asymmetric catalysis.…”