タイトルまたは説明

Titanocene dichloride is the organotitanium compound with the formula (η*-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.[1] Cp2TiCl2 does not adopt the typical "sandwich" structure like ferrocene due to the 4 ligands around the metal centre, but rather takes on a distorted tetrahedral shape
Preparation
cp2TiCl2 is a generally useful reagent that effectively behaves as a source of Cp2Ti2+. A large range of nucleophiles will displace chloride. Examples:

Cp2TiCl2 continues to be prepared from titanium tetrachloride, in the same way as its original synthesis by Wilkinson and Birmingham:[3]

The reaction is conducted in THF. Work-up sometimes washing with hydrochloric acid to convert hydrolysis derivatives to the dichloride. Recrystallization from toluene forms acicular crystals.

Cp2TiCl2 can also be prepared by using freshly distilled cyclopentadiene:

This reaction is conducted under a nitrogen atmosphere and by using THF as solvent. The product is purified by soxhlet extraction using toluene as solvent.[4]

The complex is pseudotetrahedral. Each of the two Cp rings are attached as η5 ligands. Viewing the Cp ligands as tridentate, the complex has a coordination number of 8.
Applications in organic synthesis

 

• The Petasis reagent, Cp2Ti(CH3)2, is prepared from the action of CH3MgCl or MeLi on Cp2TiCl2. This reagent is useful for the conversion of esters into vinyl ethers.
• The Tebbe's reagent Cp2TiCl(CH2)Al(CH3)2, arises by the action of 2 equivalents Al(CH3)3 on Cp2TiCl2.Reactions

  Reactions
  
  Cp2TiCl2 undergoes anion exchange reactions, e.g. to give the pseudohalides. With NaSH and with polysulfide salts, one obtains the sulfido derivatives Cp2Ti(SH)2 and Cp2TiS5.

  One Cp ligand can be removed from Cp2TiCl2 to give tetrahedral CpTiCl3. This conversion can be effected by with TiCl4 or by reaction with SOCl2.[5]
  Ti(II) derivatives
  cp2TiCl2 is a precursor to many Ti(II) derivatives. Titanocene, TiCp2, is itself so highly reactive that it is not known but it can be trapped by conducting the reduction in the presence of ligands. Reduction of titanocene dichloride results in the fulvalene complex shown in the figure.[citation needed]

   

  "Titanocene" is not Ti(C5H5)2, but this fulvalene dihydride complex.

  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.[6]

  Cp2TiCl2 + 2 CO + Mg → Cp2Ti(CO)2
  + MgCl2 Cp2TiCl2 + 2 PR3 + Mg → Cp2Ti(PR3)2 + MgCl2 Cp2TiCl2 + 2 Me3SiCCSiMe3 + Mg → Cp2TiMe3SiCCSiMe3 + MgCl2

  With only one equivalent of reducing agent, Ti(III) species result, i.e. Cp2TiCl.

  Alkyne and benzyne derivatives of titanocene are well known.[7] One family of derivatives are the titanocyclopentadienes.[8]

  Titanocene equivalents react with alkenyl alkynes followed by carbonylation and hydrolysis to form bicyclic cyclopentadienones, related to the Pauson-Khand reaction).[9] A similar reaction is the reductive cyclization of enones to form the corresponding alcohol in a stereoselective manner.[*0]

  Reduction of titanocene dichloride in the presence of conjugated dienes such as 1,*-butadiene gives η*-allyltitanium complexes.[*1] Related reactions occur with diynes. Furthermore, titanocene can catalyze C-C bond metathesis to form asymmetric diynes.[8]
  Derivatives of (C5Me5)2TiCl2

  The closest relative to titanocene-ethylene complex is that derived by Na reduction of (C5Me5)2TiCl2 in the presence of ethylene. The Cp compound cannot be made. This pentamethylcyclopentadienyl (Cp*) species undergoes many reactions such as cycloadditions of alkynes.[7]
  Medicinal uses
  Titanocene dichloride was investigated as a anticancer drug.[*2] The mechanism by which it acts is not understood, but some conjecture that it might be due to its interactions with the protein Titanocene dichloride transferrin.[*3] IUPAC name[hide] dichloridobis (η*- cyclopentadienyl) titanium Other names[hide] titanocene dichloride, dichlorobis(cyclopentadienyl)titanium(IV) Identifiers CAS number ********8 Y RTECS number XR******0 Properties Molecular formula C*0H*0Cl2Ti Molar mass **8.*6 g/mol Appearance bright red solid Density 1.*0 g/cm3, solid Melting point **9 °C