Reactions of co-ordinated ligands. Part 23. Metalla-ring-forming reactions between hexafluoroacetone and η4-1,3-diene(η5-indenyl)rhodium complexes; the crystal and molecular structures of [Rh{OC(CF3)2CH2C(Me)CHCH2}(η5-C9H7)] and [Rh{OC(CF3)2C3H3C6H4}(η4-trans-C4H4Me2-1,4)]

Abstract

Reaction (room temperature) of hexafluoroacetone with isoprene- or 2,3-dimethylbuta-1,3-diene-(η⁵-indenyl)-rhodium affords respectively the η³-allylic rhodium(III) complexes [[graphic omitted](R²)CH₂}(η⁵-C₉H₇)](1a; R¹= Me, R²= H), (1b; R¹= H, R²= Me)(ratio 5 : 1), and (2; R¹= R²= Me). A single-crystal X-ray diffraction study of (1a) showed that the crystals are monoclinic, space group P2₁/a, with Z= 4 in a unit cell of dimensions a= 14.020(7), b= 8.690(4), c= 14.669(5)Å, and β= 101.61(3)°. The structure has been solved by heavy-atom methods from automated diffractometer data, and refined to R 0.045 (R′ 0.056) for 2 704 reflections. The rhodium adopts an essentially octahedral geometry arising from η⁵ bonding of an indenyl ligand, a η³-allylic group formed from linking of the isoprene to the hexafluoroacetone, and a rhodium–oxygen σ bond. trans,trans-Hexa-2,4-diene(η⁵-indenyl)rhodium reacts with hexafluoroacetone via a different reaction path to form the rhodium(I) complex (3). A single-crystal X-ray diffraction study of (3), a tris olefin complex, showed that the crystals are monoclinic, space group P2₁/c with Z= 4 in a unit cell of dimensions a= 8.094(2), b= 16.962(8), c= 12.782(4)Å, and β= 99.81 (2)°. The structure has been refined to R 0.021 (R′ 0.025) for 2 878 reflections. The rhodium adopts an essentially square-planar configuration the co-ordination sites being occupied by a η⁴-bonded trans,trans-hexa-2,4-diene, a η²-bonded indenyl ligand, and an oxygen atom of the hexafluoroacetone molecule σ bonded to rhodium. The hexafluoroacetone is bonded to the C₅ ring of the indenyl ligand. The mechanism of formation of these complexes is discussed. In contrast, hexafluoroacetone reacts with bis(ethylene)(η⁵-indenyl)rhodium to form ethyl(hexafluoroacetylacetonato)(η⁵-indenyl)rhodium.