Platinum and iron complexes of pentamethylcyclopentadiene and related ligands

Abstract

Hexamethylbicyclo[2,2,0]hexa-2,5-diene reacts with [Pt(C₂H₄)Cl₂]₂ to give dichloro(hexamethylbicyclo[2,2,0]hexa-2,5-diene)platinum and with K₂PtCl₄, under acidic conditions, to give dichloro(pentamethylcyclopentadiene)platinum, (III). The latter complex is also obtained from reaction of K₂PtCl₄ with C₅Me₅CHXMe (X = H, Cl, OMe, or OEt) in acidic methanol. A mechanism is suggested for these reactions. A mixture of (III) and dichloro(pentamethyl-5-vinylcyclopentadiene)platinum, (VI), is obtained on reaction of C₅Me₅CHXMe with [Pt(C₂H₄)Cl₂]₂ in aprotic solvents. Complex (VI) is the sole product from a similar reaction with pentamethyl-5-vinylcyclopentadiene, and an analogous complex is obtained from 5-ethylpentamethylcyclopentadiene. The stereochemistries of these complexes have been determined. The pentamethylvinylcyclopentadiene complex (vinyl endo-) undergoes an unusual hydrogen-catalysed reaction to give the isomeric complex with vinyl exo- to the metal. Reaction of (III) with Fe₃(CO)₁₂ gave [Fe(C₅Me₅)(CO)₂]₂ and endo-H Fe(C₅Me₅H)(CO)₃.