Synthesis of chiral-at-metal half-sandwich ruthenium(II) complexes with the CpH(PNMent) tripod ligand

Treatment of the chiral tripod ligand (LMent,SC)-CpH(PNMent) with (Ph3P)3RuCl2 in ethanol afforded the two chiral-at-metal diastereomers (LMent,SC,RRu)- and (LMent,SC,SRu)-[Cp(PNMent)Ru(PPh3)Cl] (70% de) in which the cyclopentadienyl group and the P atom of the ligand coordinated at the metal center. The (LMent,SC,RRu)-diastereomer was isolated by crystallization from ethanol–pentane and its structure was established by X-ray crystallography. The (LMent,SC,RRu)-diastereomer epimerized in CDCl3 solution at 60 °C in a first-order reaction with a half-life of 5.66 h. In alcoholic solution epimerization occurred at room temperature. Substitution of the chloride ligand in (LMent,SC,RRu)- and (LMent,SC,SRu)-[Cp(PNMent)Ru(PPh3)Cl] by nitriles NCR (R = Me, Ph, CH2Ph) in the presence of NH4PF6 gave mixtures of the diastereomers (LMent,SC,RRu)- and (LMent,SC,SRu)-[Cp(PNMent)Ru(PPh3)NCR]PF6. Treatment of (LMent,SC,RRu)- and (LMent,SC,SRu)-[Cp(PNMent)Ru(PPh3)Cl] with piperidine or morpholine in the presence of NH4PF6 led to the chiral-at-metal diastereomers (LMent,SC,RRu)- and (LMent,SC,SRu)-[Cp(PNMent)Ru(PPh3)NH3]PF6 (6% de).