[CpRu(η ⁶-naphthalene)]PF ₆ as precursor in complex synthesis and catalysis with the cyclopentadienyl-ruthenium(II) cation

The complex [CpRu(η ⁶-naphthalene)]PF6 (2) is a readily accessible and air-stable source of the CpRu ⁺ fragment (Cp = η ⁵C ₅H ₅) 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 A-TRISPHAT to give [CpRu(η ⁶-naphthalene)]A- TRISPHAT (4; with X-ray crystal structure). Ligand exchange of 2 in acetonitrile with (Z,Z)- 1,5-cyclooctadiene (COD) produces [CpRu(η ²: η ²-COD)(MeCN)]PF ₆ (5; with X-ray crystal structure); with chelating phosphanes (P-P), complexes [CpRu(P-P)(MeCN)]PF ₆ are selectively generated, and starting with a 1,4-diazadiene, a solvento complex [CpRu(diazadiene-N,N ^′)(MeCN)]PF ₆ is obtained. Stepwise reaction of 2 (or 4) in acetonitrile with different monodentate phosphanes PR ₃ and PR' ₃ first gives [CpRu(PR ₃)(MeCN) ₂] ⁺ (I), then the chiral-at-metal cation [CpRu(PR ₃)(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 η ¹-p or the chelating η ²-P,N coordination mode, depending on the size of the ligand and, in solution, the solvent. Reaction of 2 with 3 equiv of triarylphosphanes (PR ₃) in hot acetone gives rise to [CpRu(PR ₃) ₃] ⁺, including the previously unknown cation [CpRu(PPh ₃) 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.