Synthesis of indenyl-ruthenium(II) σ-alkynyl complexes via nucleophilic addition of (1R)-(+)- and (1S)-(−)-camphor enolates on the allenylidene group of [Ru(CCCPh2)(η5-C9H7)(PPh3)2][PF6]: Efficient synthesis of novel optically pure vinylidene derivativ

The diphenylallenylidene complex [Ru(CCCPh2)(η5-C9H7)(PPh3)2][PF6] (1) regioselectively reacts at the Cγ atom with the lithium enolate derived from (1R)-(+)-camphor to yield σ-alkynyl derivative [Ru{CCCPh2(C10H15O)}(η5-C9H7)(PPh3)2] (2). Complex 2 was obtained as a non-separable mixture of two diastereoisomers, i.e. (1R,3S,4R)-2 and (1R,3R,4R)-2 (ca. 3:2 ratio), in which the alkynyl fragment is located in exo or endo disposition on the camphor skeleton, respectively. Protonation of this mixture with HBF4·Et2O affords the vinylidene derivative [Ru{CC(H)CPh2(C10H15O)}(η5-C9H7)(PPh3)2][BF4] (3) as a single diastereoisomer, i.e. (1R,3S,4R)-3, showing an exo disposition of the vinylidene group. The structure of complex (1R,3S,4R)-3 has been confirmed by X-ray diffraction. The molecular structure shows the typical pseudo-octahedral three-legged piano-stool geometry around the ruthenium atom, which is linked to the phosphorus atoms of the PPh3 ligands, to the η5-bonded indenyl ligand, and to an almost linear vinylidene chain (RuC(1)C(2)=165.6 (18)°) with a RuC(1) bond length of 1.88 (2) Å. Demetalation of (1R,3S,4R)-3, by treatment with acetonitrile at reflux, yields the terminal alkyne HCCCPh2(C10H15O) (4) and the nitrile complex [Ru(NCMe)(η5-C9H7)(PPh3)2][BF4] (5). Compound 4 was obtained as a non-separable mixture of two diastereoisomers, i.e. (1R,3S,4R)-4 and (1R,3R,4R)-4 (ca. 3:1 ratio). Related reactions starting from diphenylallenylidene 1 and the (1S)-(−)-camphor enolate are also reported.