η6-Arene-stabilized ruthenacyclopentanes: synthesis, X-ray structures, and reaction with the trityl cation

Abstract

The ruthenacyclopentane complexes [[graphic omitted](η⁶-C₆Me₆)L][L = PPh₃(2a), PMePh₂(2b), or PMe₂Ph(2c)] have been prepared by reacting the corresponding dichlororuthenium derivatives with an excess of 1,4-dilithiobutane. Their crystal structures have been determined: (2a) and (2b) have space group P2₁/n crystals, while (2c) crystallizes in space group P2₁/c. Cell constants: (2a), a= 9.249(3), b= 16.160(7), c= 19.094(21)Å, β= 90.70(1)°, Z= 4, and R(3 203 reflections, 453 parameters)= 0.0425; (2b), a= 17.463(13), b= 8.708(6), c = 17.749(13)Å, β= 109.15(4)°, Z= 4, and R(3 412, 436)= 0.0395; (2c), a= 9.575(6), b= 11.899(8), c= 19.494(12)Å, β= 97.96(2)°, Z= 4, and R(3 080, 383)= 0.0330. All compounds possess structures of the ‘three-legged piano stool’ type, and the metallacyclopentane ring is puckered having a twisted conformation which is intermediate between the envelope and half-chair forms. The orientations of the hexamethylbenzene and phosphine ligands are considered with respect to the minima of the van der Waals conformation energies of the free molecules. The ruthenacyclopentanes-(2a)–(2c) react at room temperature with [CPh₃][BF₄] to give the η³-allylic complexes [Ru(η³-CH₂CHCHMe)(η⁶-C₆Me₆)L][BF₄][L = PPh₃(3a), PMePh₂(3b), or PMe₂Ph (3c)].