Titanocene dichloride

Titanocene dichloride is the organotitanium compound with the formula (η5-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. Titanocene dichloride is the organotitanium compound with the formula (η5-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. 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 standard preparations of Cp2TiCl2 start with titanium tetrachloride. The original synthesis by Wilkinson and Birmingham uses sodium cyclopentadienide is still commonly used: It can also be prepared by using freshly distilled cyclopentadiene rather than its sodium derivative: Cp2TiCl2 is a generally useful reagent that effectively behaves as a source of Cp2Ti2+. A large range of nucleophiles will displace chloride. With NaSH and with polysulfide salts, one obtains the sulfido derivatives Cp2Ti(SH)2 and Cp2TiS5. 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. One Cp ligand can be removed from Cp2TiCl2 to give tetrahedral CpTiCl3. This conversion can be effected with TiCl4 or by reaction with SOCl2. Titanocene itself, TiCp2, is so highly reactive that it rearranges into a TiIII hydride dimer and has been the subject of much investigation. 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, μ(η5:η5-fulvalene)-di-(μ-hydrido)-bis(η5-cyclopentadienyltitanium), 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.