Thermodynamically Controlled Formation of Diastereopure Three-Legged Piano-Stool Complexes. The Substitution Chemistry of [RuCp(aminophosphinoferrocene)(CH₃CN)]PF₆

Treatment of [RuCp(CH₃CN)₃]⁺ with the chiral ligands PN* = (R_c,S_pl)-2-(1-N,N-dimethylaminoethyl)-1-diphenylphosphinoferrocene, (S_pl)-2-(N,N-dimethylaminomethyl)-1-diphenylphosphinoferrocene, and (R_c,S_pl)-2-(1-N,N-diethylaminoethyl)-1-diphenylphosphinoferrocene affords diastereoselectively the labile cationic complexes [(S_Ru)-RuCp(PN*)(CH₃CN)]⁺. The exchange kinetics of CH₃CN has been studied as a function of temperature, revealing a dissociative mechanism, and therefore thermodynamic control is responsible for the diastereoselective formation of [(S_Ru)-RuCp(PN*)(CH₃CN)]⁺. These react with HC⋮CPh to give the chiral vinylidene complexes [(R_Ru)-RuCp(PN*)(CCHPh)]⁺ in highly diastereoselective fashion. With CO complexes [RuCp(PN*)(CO)]⁺ are obtained in high yields but with significantly decreased stereoselectivity due to kinetic control of the substitution reaction. Under photochemical conditions epimerization occurs to give [(R_Ru)-RuCp(PN*)(CO)]⁺ with a de of >98%. In the case of [RuCp((R_c,S_pl)-2-(1-N,N-diethylaminoethyl)-1-diphenylphosphinoferrocene)(CO)]⁺, the diastereomeric excess increases from 87 to >98% upon heating due to an intramolecular epimerization. The absolute configuration of representative complexes has been determined by X-ray crystallography.