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 derivatives

The diphenylallenylidene complex [Ru(=C=C=CPh2)(eta(5)-C9H7)(PPh3)(2)][PF6] (1) regioselectively reacts at the C-gamma atom with the lithium enolate derived from (1R)-(+)-camphor to yield sigma-alkynyl derivative [Ru{CdropCCPh(2)(C10H15O)}(n(5)-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 (HBF4Et2O)-Et-. affords the vinylidene derivative [Ru{=C=C(H)CPh2(C10H15O)}(eta(5)-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 eta(5)-bonded indenyl ligand, and to an almost linear vinylidene chain (Ru-C(1)-C(2) = 165.6 (18)degrees) with a Ru-C(1) bond length of 1.88 (2) A. Demetalation of (1R,3S,4R)-3, by treatment with acetonitrile at reflux, yields the terminal alkyne HCdropCCPh(2)(C10H15O) (4) and the nitrile complex [Ru(NdropCMe)(eta(5)-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. (C) 2002 Elsevier Science B.V. All rights reserved.