Lithium pentamethylcyclopentadienyl

Pentamethylcyclopentadienyl) ( j5-cyclopentadienyl) iron has been prepared by the alkylation of ferrocene under Friedel-Crafts conditions with methylchloride,1 and also by reaction of ferrous chloride or FeBr2 DME (DME = 1,2-dimethoxyethane) with equimolar quantities of pentamethyl-cyclopentadienyl sodium and cyclopentadienyl lithium.2,3... 

A 100-mL, two-necked, round-bottomed flask with a stirring bar, a nitrogen inlet, and a rubber septum is evacuated and filled with nitrogen three times. Iron(II) bis(acetylacetonate) (2.01 g, 7.9 mmol) is added to the flask in a nitrogen bag. Then 20 mL of anhydrous THF, freshly distilled from Na/benzo-phenone under nitrogen, is added to the flask, the stirring is started, and the dark yellowish-brown solution is cooled to — 78°C with a dry ice/ acetone bath. A suspension of pentamethylcyclopentadienyl lithium (1.125 g, 7.9 mmol) in 20 mL of anhydrous THF is added to the reaction flask via syringe. The purity and the stoichiometric amount of pentamethylcyclopentadienyl lithium are crucial to avoid side reactions. 

Caution. Pentamethylcyclopentadienyl lithium is pyrophoric and must be handled with care under an inert atmosphere. 

Reaction of dichloro(pentamethylcyclopentadienyl)silane with lithium, sodium or potassium naphthalenide gives a mixture of elemental silicon, the corresponding alkali metal pentamethylcyclopentadienide and decamethylsilicocene (82) (equation 64)181. Compound 82 is formed as the only product in the reduction of dibromo-bis(pentamethylcyclopentadienyl)silane with potassium anthracenide (equation 65)182. 

Pentamethylcyclopentadiene is a useful aromatic building block for the preparation of other compounds. It can be converted to many salts of its conjugate base with alkali metals or strong bases such as butyl lithium.4 These pentamethylcyclopentadienyl anion salts as well as the diene itself can be transformed into n -pentamethylcyclopentadienyl ligands of organotransition metal complexes by many known methods.4... 

Pentamethylcyclopentadienyllanthanide dichlorides Cp -LnCE (Ln = Sm, Lu) react with diarylbutadienes and lithium under elimination of the pentamethylcyclopentadienyl... 

The methyl(pentamethylcyclopentadienyl)aluminum chloride dimer, [(C5Me5)MeAlCl]2, is prepared from reaction of dimethylaluminum chloride with (pentamethylcyclopentadienyl)lithium in toluene. The solid-state structure of this compound reveals that the CyMey ligand interacts with the aluminum centers in an rf fashion across /i-chloro bridges. 

Di(pentamethylcyclopentadienyl)tin(II) (decamethylstannocene, Cp 2Sn ) can be obtained from Cp Br and Sn, or Cp M and SnCl2, or by reducing Cp 2SnCl2 with lithium naphthalenide or dilithium cyclooctatetraendiide.100... 

A C-enriched cyclopropane containing a C-Rh bond was prepared by treating [l- C]bro-mocyclopropane successively with lithium and diiodo( y -pentamethylcyclopentadi-enyl)(trimethylphosphane)rhodium in tetrahydrofuran (t/ -pentamethylcyclopentadienyl)(tri-methylphosphane)([l- C]cyclopropyl)rhodium was isolated in 91% yield. 

Preparation.—From Halogenophosphines and Organometallic Reagents. A series of trimethylsilylcyclopentadienylphosphines, e.g. (1), has been prepared from the appropriate trimethylsilylcyclopentadienyl-lithium and halogenophosphine. Similarly, the reaction of pentamethylcyclopentadienyl-lithium with chlorodimethyl-phosphine gives the phosphine (2), which is reported to be thermally stable. ... 

In preparation of di-g-methylenebis(methyl-pentamethylcyclopentadienyl)dirhod-ium complexes by aerobic oxidation of a solution of the halocomplex and methyl-lithium or trimethylaluminium in ether-benzene, the reaction mixture occasionally ignited and burned violently. Full precautions and a working scale below 1 mmol are recommended. 

The foregoing hypothesis requires that ligand exchange on the lithium cation be slow under the conditions of the experiments described. In fact, there is little information available in the literature on this point. Just recently, however, there has been a convincing demonstration that lithium exchange on a lithium cation can be very slow. Dr. Patricia Watson, of the Central Research Department at the Dupont company, prepared an organometallic complex by addition of bis(pentamethylcyclopentadienyl)methylytterbium to a THF solution of methyllithium. (1 ) The product is a crystalline 1 1 adduct, which was recrystallized from diethyl ether and subjected to single crystal x-ray analysis. The structure of the recrystallized material is as follows ... 

---