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Titanocene dichloride is the organotitanium compound with the formula (hapticity-C5H5)2TiCl2, commonly abbreviated as Cp2TiCl2. This metallocene is a common reagent in organometallic and organic synthesis. It exists as a bright red solid that slowly hydrolyzes in air. It shows antitumour activity and was the first non-platinum complex to undergo clinical trials as a chemotherapy drug.
It can also be prepared by using freshly distilled cyclopentadiene rather than its sodium derivative:
Focusing on the geometry of the Ti center, Cp2TiCl2 adopts a distorted tetrahedral geometry (counting Cp as a monodentate ligand). The Ti-Cl distance is 2.37 Å and the Cl-Ti-Cl angle is 95°.
The Petasis reagent, Cp2Ti(CH3)2, is prepared from the action of methylmagnesium chloride or methyllithium on Cp2TiCl2. This reagent is useful for the conversion of esters into vinyl ethers.
The Tebbe reagent Cp2TiCl(CH2)Al(CH3)2, arises by the action of 2 equivalents Al(CH3)3 on Cp2TiCl2. (1982). 9780120311200 ISBN 9780120311200
The sandwich complex (Cycloheptatrienyl)(cyclopentadienyl)titanium is prepared by treatment of titanocene dichloride with lithium cycloheptatrienyl.
Titanocene itself, TiCp2, is so highly reactive that it rearranges into a TiIII hydride dimer and has been the subject of much investigation. (2025). 9788122412581, New Age International Publishers. ISBN 9788122412581 This dimer can be trapped by conducting the reduction of titanocene dichloride in the presence of ligands; in the presence of benzene, a fulvalene complex, can be prepared and the resulting solvate structurally characterised by X-ray crystallography. The same compound had been reported earlier by a lithium aluminium hydride reduction and sodium amalgam reduction of titanocene dichloride, and studied by 1H NMR prior to its definitive characterisation.
Cp2TiCl2 is a precursor to TiII derivatives. Reductions have been investigated using Grignard reagent and alkyl lithium compounds. More conveniently handled reductants include Mg, Al, or Zn. The following syntheses demonstrate some of the compounds that can be generated by reduction of titanocene dichloride in the presence of π acceptor ligands:
Alkyne derivatives of titanocene have the formula (C5H5)2Ti(C2R2) and the corresponding are known. One family of derivatives are the titanocyclopentadienes. Rosenthal's reagent, Cp2Ti(η2-Me3SiC≡CSiMe3), can be prepared by this method. Two structures are shown, A and B, which are both resonance contributors to the actual structure of Rosenthal's reagent.
Titanocene equivalents react with alkenyl alkynes followed by carbonylation and hydrolysis to form bicyclic cyclopentadienones, related to the Pauson–Khand reaction. A similar reaction is the reductive cyclization of enones to form the corresponding alcohol in a stereoselective manner.
Reduction of titanocene dichloride in the presence of conjugated such as 1,3-butadiene gives η3-allyltitanium complexes. Related reactions occur with diynes. Furthermore, titanocene can catalyze C–C bond metathesis to form asymmetric diynes.
Titanocene dichloride as a photoredox catalyst to open epoxides in green light.
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