Synthesis And Properties Of The Carbon-bridged Bis(cyclopentadienyl) Lanthanide Complexes

A spiro carbon-bridged bis?cyclopentadiene?compound was synthesized from cyclohexanone and cyclopentadiene.Using this compound as the supporting ligand,carbon-bridged bis?cyclopentadienyl?lanthanide cyclopentadienyl complex,carbon-bridged bis?cyclopentadienyl?lanthanide amide and carbon-bridged bis?cyclopentadienyl?cerium?IV?complex were synthesized.They were characterized by IR,elemental analyses and NMR spectroscopy.Moreover,their catalytic behaviors were investigated.?1?Reaction of the cyclohexanone with two equivalents of cyclopentadiene in THF with NaOH powder as the catalyst,afforded a spiro carbon-bridged bis?cyclopentadiene?ligand of?CH₂?₅C?C₅H₅?₂.Reaction of this spiro carbon-bridged bis?cyclopentadiene?containing small amount of pentamethylenefulvene?C₅H₄?C?CH₂?₅ with metallic sodium led to linked bis?cyclopentadienyl?sodium and a few linked tri?cyclopentadienyl?sodium.The molar ratio of linked bis?cyclopentadienyl?sodium and linked tri?cyclopentadienyl?sodium was about 4:1.?2?Reaction of the mixture of linked bis?cyclopentadienyl?sodium and linked tri?cyclopentadienyl?sodium with YbCl₃ in THF according to Na:Yb=3:1 afforded a binuclear lanthanide complex of{?CH₂?₅C??⁵-C₅H₄?₂Yb}₂??⁵-C₅H₄?C?CH₂?₅??-?¹:?¹-C₅H₄?C?CH₂?₅??⁵-C₅H₄?.The complex was characterized by IR,elemental analyses and X-ray crystallography.?3?Reaction of LnCl₃?Ln= Nd,Sm,Er?firstly with a equivalent of?CH₂?₅C?C₅H₄Na?₂ in THF,then with one equivalent of NaN?TMS?₂ led to the solution of?CH₂?₅C?C₅H₄?₂LnN?TMS?₂?Ln= Nd,Sm,Er?.Polymerization of MMA catalyzed by?CH₂?₅C?C₅H₄?₂LnN?TMS?₂?Ln= Nd,Sm,Er?was studied.The activity of Er complex is much higher than that of Nd and Sm complex.The reactions can be carried out over a quite broad temperature range.The highest polymerization temperature is 75 ?.The polymerization process is not living,and the tacticity of PMMA is mainly syndiotactic when the polymerization reaction is rather low.?4?Linked bis?cyclopentadienyl?cerium?IV?complex [?CH₂?₅C?C₅H₄?₂]₂Ce was prepared from Ce?OCMe₃?₄ and two equivalents of the neutral ligand?CH₂?₅C?C₅H₅?₂ in THF,and Ce?OCMe₃?₄ was synthesized from?NH₄?₂Ce?NO₃?₆ and six equivalents of NaOCMe₃.The complex was characterized by IR,elemental analyses and X-raycrystallography.It is not sensitive toward air and/or moisture,which is totally different from the departed cyclopentadienyl-lanthanide complexes.It is well soluble in most of organic solvents.The complex is thermally stable.When heated in the nitrogen atmosphere,it does not decompose until 290 ?.In air,it starts to decompose at 230 ?.The complex is also electrochemical stable.When DMF and CH₃CN were usded as the solvents,there were not any characteristic redox peaks found.?5?Oxidation of benzoin catalyzed by the complex [?CH₂?₅C?C₅H₄?₂]₂Ce was investigated with the ceric ammonium nitrate?CAN?as a contrast.When the reaction temperature is below 80 ?,the catalytic activity of [?CH₂?₅C?C₅H₄?₂]₂Ce is better than CAN.The best reaction temperature is 80 ?,and the best reaction time is 3 h.