eta-6-Arene-stabilized Ruthenacyclopentanes: Syntesis, X-Ray Structures, and Reaction with the Trityl Cation

The ruthenacyclopentane complexes [Ru(CH2CH2CH2CH2)(η 6-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)]