Reactions of co-ordinated ligands. Part 25. The synthesis of µ-allene-dicarbonylbis(η5-indenyl)dirhodium and protonation to form a bridged cationic vinyl complex; molecular structures of µ-allene-dicarbonylbis(η5-indenyl)dirhodium and dicarbonyl-bis(η5-indenyl)-µ-(1-methylvinyl)-dirhodium(Rh–Rh) tetrafluoroborate

Abstract

Reaction (60 °C) of tri-µ-carbonyl-tris(η⁵-indenyl)-triangulo-trirhodium with allene in toluene as solvent affords µ-allene-(dicarbonyl)bis(η⁵-indenyl)dirhodium. An X-ray crystallographic study was carried out on this complex. Crystals are triclinic, space group P, in a unit cell of dimensions a= 12.148(5), b= 10.682(5), c= 9.620(5)Å, α= 115.84(3), β= 121.09(4), γ= 82.25(4)°, and Z= 2. The structure has been refined to R 0.024 (R′ 0.026) for 5 027 unique reflections to 2θ⩽ 60.0°. The allene group bridges the metal atoms, which are not bonded [Rh(1)⋯ Rh(2) 3.711(1)Å]. Reaction of this complex with HBF₄–Et₂O affords in high yield the cationic species dicarbonylbis(η⁵-indenyl)-µ-(1-methylvinyl)-dirhodium tetrafluoroborate, which was identified by X-ray crystallography. Crystals are monoclinic, space group P2₁/n, in a unit cell of dimensions a= 13.851(5), b= 15.207(6), c= 12.652(3)Å, β= 110.62(2)°, and Z= 4. The structure has been refined to R 0.036 (R′ 0.039) for 4 932 reflections at 240 K to 2θ⩽ 60°. Protonation has occurred at an end carbon atom of the allene to form [Rh₂-(µ-CO)(CO){µ-C(Me)CH₂}(η⁵-C₉H₇)₂][BF₄] with a Rh–Rh bond length of 2.693(1)Å.