[CpRu(η⁶-naphthalene)]PF₆ as Precursor in Complex Synthesis and Catalysis with the Cyclopentadienyl-Ruthenium(II) Cation

The complex [CpRu(η6-naphthalene)]PF6 (2) is a readily accessible and air-stable source of the CpRu+ fragment (Cp = η5-C5H5) for applications in complex synthesis and catalysis. The utility of this precursor complex is demonstrated in a number of experiments: The counterion of 2 is exchanged by reaction with cinchonidinium Δ-TRISPHAT to give [CpRu(η6-naphthalene)]Δ-TRISPHAT (4; with X-ray crystal structure). Ligand exchange of 2 in acetonitrile with (Z,Z)-1,5-cyclooctadiene (COD) produces [CpRu(η2:η2-COD)(MeCN)]PF6 (5; with X-ray crystal structure); with chelating phosphanes (P−P), complexes [CpRu(P−P)(MeCN)]PF6 are selectively generated, and starting with a 1,4-diazadiene, a solvento complex [CpRu(diazadiene-N,N′)(MeCN)]PF6 is obtained. Stepwise reaction of 2 (or 4) in acetonitrile with different monodentate phosphanes PR3 and PR′3 first gives [CpRu(PR3)(MeCN)2]+ (I), then the chiral-at-metal cation [CpRu(PR3)(PR′3)(MeCN)]+ (II), which was resolved spectroscopically (31P NMR) when combined with the enantiopure Δ-TRISPHAT counterion. Complex cations of type I or II incorporating 2-diphenylphosphinopyridines as ligands display either the η1-P or the chelating η2-P,N coordination mode, depending on the size of the ligand and, in solution, the solvent. Reaction of 2 with 3 equiv of triarylphosphanes (PR3) in hot acetone gives rise to [CpRu(PR3)3]+, including the previously unknown cation [CpRu(PPh3)3]+. The in situ combination of 2 and 2 equiv of bulky 6-substituted 2-pyridylphosphanes catalyzes the anti-Markovnikov hydration of terminal alkynes to aldehydes. Either complex 2 or 5 catalyzes the [2+2+2]-cycloaddition of COD with alkynes. Complex 5 is a catalyst for the coupling of allyl alcohols with terminal alkynes to give 4-alkenones.