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

Abstract

Treatment of [RuCp(CH3CN)3]+ with the chiral ligands PN* = (Rc,Spl)-2-(1-N,N-dimethylaminoethyl)-1-diphenylphosphinoferrocene, (Spl)-2-(N,N-dimethylaminomethyl)-1-diphenylphosphinoferrocene, and (Rc,Spl)-2-(1-N,N-diethylaminoethyl)-1-diphenylphosphinoferrocene affords diastereoselectively the labile cationic complexes [(SRu)-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 [(SRu)-RuCp(PN*)(CH3CN)]+. These react with HC⋮CPh to give the chiral vinylidene complexes [(RRu)-RuCp(PN*)(CCHPh)]+ 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 [(RRu)-RuCp(PN*)(CO)]+ with a de of >98%. In the case of [RuCp((Rc,Spl)-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.