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-(1-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.