Synthesis of η 5-1,2,3,4,5-pentamethylcyclopentadienyl-platinum complexes

Abstract

Reaction of K 2PtCl 4 with pentamethylcyclopentadiene gave the exo-H isomer ( 1b, 25%) as well as the endo-H isomer ( 1a, 75%) of [Pt(η 4-C 5Me 5H)Cl 2]. The mixture reacted with AgBF 4 in acetone at −78°C to give the mixed endo-H, exo-H isomeric dication solvate complexes [Pt(η 4-C 5Me 5H)(acetone) x] 2+(BF 4 −) 2 ( 2a, b), which decompose at room temperature to give [Pt(η 4-C 5Me 5H)(η 5-C 5Me 5)] +BF 4 − ( 3). The same reaction of 1a, b in the presence of dienes (pentamethylcyclopentadiene, cyclopentadiene, 1,3-cyclohexadiene, and 1,5-cyclooctadiene) occurs with spontaneous deprotonation to give the monocationic complexes, 3, [Pt(η 4-C 5Me 5H)(η 5-C 5Me 5)] +BF 4 − ( 4a, b), [Pt(η 4-C 6H 8)(η 5-C 5Me 5)] +BF 4 − ( 5), and [Pt(η 4-C 8H 12)(η 5-C 5Me 5)] +BF 4 − ( 6 ), respectively, in high yield. The products from the reaction depend on the ability of the coordinated diene to undergo deprotonation in an intermediate, in the order, η 4-1,3-cyclohexadiene ∼η 4-1,5-cyclooctadiene < η 4- endo-pentamethylcyclopentadiene < η 4- exo-pentamethylcy- clopentadiene < η 4-cyclopentadiene. The solvent complexes [M(η 5-C 5Me 5)(acetone) 3] 2+(BF 4 −) 2 (M  Rh, Ir) react with C 5Me 5H to give decamethyl-rhodocenium and -iridocenium salts.