Reactivity to Lewis acids of half-sandwich pentamethylcyclopentadienyl complexes of ruthenium(II) containing chiral diphosphines

Compounds (η5-C5Me5)Ru(L∧L)Cl (where L∧L is 1,2-bis(diphenylphosphino)ethane or chiral homologs thereof) form adducts with BCl3 and BBr3 with 1:2 stoichiometry, whereas no stable compounds are obtained with AlX3 (X = Cl, Br).When the metal is a center of chirality, i.e., for complexes containing diphosphines with C1 symmetry such as (R)-prophos, the reaction takes place with a high grade of diastereoselectivity (diastereomeric ratio 92/8). Starting with either a 50:50 or a 95/5 initial mixture, the predominant diastereomer formed has a larger difference in the 31P{1H} NMR chemical shift.

Complexes of the type (η5-C5Me5)Ru(L∧L)Cl (L∧L is 2PPh3, 1,2-bis(diphenylphosphino)ethane, or chiral homologs thereof) react instantly with an excess of BCl3 or BBr3 in dichloromethane solution forming adducts that have a 1:2 stoichiometry. No stable compounds are obtained with AlX3 (X = Cl, Br). For compounds containing a diphosphine having a C1 symmetry, in which the metal is a stereogenic center, the reaction takes place stereoselectively.Figure optionsDownload as PowerPoint slide