Further studies on metal-promoted vinylcyclopropane to cyclopentene rearrangements. Structure and thermolysis of rhodium complexes of exo-6-vinylbicyclo[3.1.0]hex-2-ene and the crystal structure of the 1,6–8-η4-5-allylcyclopent-2-enyl(hexafluoroacetylacetonato)rhodium(III) tetramer

Abstract

The reactions of exo-6-vinylbicyclo[3.1.0]hex-2-ene with bis(ethylene)rhodium(I) complexes lead to displacement of ethylene and formation of ring-opened σπ-bis-allylrhodium derivatives. The hexafluoroacetylacetonate (11) is tetrameric in the solid state and its structure has been determined by X-ray methods. Crystals of [C₁₃H₁₁F₆RhO₂]₄ are monoclinic, space group P2₁/c, a= 19.641(7), b= 14.353(7), c= 44.87(1)Å, β= 98.03(3), Z= 8; 3 266 observed reflections [I/σ(I) > 3.0] were collected by diffractometer and refined to R 0.077.

The four rhodium atoms form the corners of a puckered square and are each π-bonded to one hydrocarbon at C(2),C(3) and to another σ at C(1) and π at C(6)–(8). This complex rearranges in acetone solution at 338 K, mainly to the corresponding derivative of bicyclo[3.3.0]octa-2,6-diene; thermolysis of the corresponding dimeric acetylacetonate (12) has been studied in detail by ¹H n.m.r. The reaction exhibits half-order kinetics over the conentration range 0.02–0.2M in deuteriobenzene, rearranging rapidly (t_1/2[0.205M] 30.30 min) to a mixture of acetylacetonato(bicyclo[3.3.0]octa-2,6-diene)rhodium(I)(2) and acetylacetonato-(endo-6-vinylbicyclo[3.1.0]hex-2-ene)rhodium(I)(1) in 88 : 12 ratio. In deuteriodichloromethane, the ratio is 33 : 67. The cyclopentadienyl complex (14) is monomeric, and thermally stable below 373 K. Reaction of the rhodium chloride complex (13) with bicyclo[2.2.1]hepta-2,5-dienesilver hexafluorophosphate leads directly to a rearranged cation (17) at 273 K.

The mechanisms of these transformations are discussed.