Metal tetrachlorides, reactions

Titanium tetrachloride is a very effective catalyst for the addition of LiAlH4 or alane to the olefinic double bond. The mechanism of this reaction involves intermediate transition metal hydrides, as in the case of reaction of NaBPU and Co11-salts. The hydrotitanation of the double bonds is probably followed by a rapid metal exchange reaction (Scheme 3)94. 

The preparation of Th, U and Np tetracyclopentadienides were accomplished by the straightforward reaction of the anhydrous metal tetrachloride with potassium cyclopentadienide in benzene (6). Tetrakis(cyclopentadienyl) pro-tactinium(IV) was prepared using Be(CsH5)2 and Pads prepared in situ (6). Infrared data suggest that aU of the tetracyclopentadienides possess similar molecular structures the Th, U and Np complexes were found to be isostmctural by powder techniques (79, 80). 

Compounds of composition [CsH5NH]2[MCl4(OMe)2] (M = Zr or Hf), [C5H5NH]2-[ZrCl5(OEt)] and [CsHsNH]2[ZrCl2(OEt)4] have been prepared by reaction of the metal tetrachlorides with methanol or ethanol in the presence of pyridine.214... 

Zirconium(IV) and hafnium(IV) tetrakis(tetrahydroborates) M(BH4)4 are of interest as extremely volatile, covalent complexes that contain tridentate BH ligands and exhibit rapid intramolecular exchange of bridging and terminal hydrogen atoms. 4,615 These compounds were prepared initially from NaMF5 (M = Zr or Hf) and excess A1(BH4)3 (equation 53),616 but they are obtained more conveniently from the reaction of the anhydrous metal tetrachloride with excess lithium tetrahydroborate (equation 54), either in the solid state617,618 or in the presence of a small amount of diethyl ether.619... 

Compounds of the type M(NR2)4 (M = Th or U) are obtained by reaction of the metal tetrachloride with LiNR2 in non-aqueous solvents. They are all highly reactive towards protonated species and they readily undergo C02, COS, CS2 or CSe2 insertion into the M—N bond to form carbamates. 

The proposed hydride formation is conlirmed by the results of interaction with carbon tetrachloride. Reaction with CCI4 (equation 12.8) is a generally accepted test for metal-hydrogen (M-H) bonds (25). 

Depending on the nature of the metal (M), the initial metal chloride (MC1 ) or a product MClj j,(OR)j, forms an addition complex with alcohol molecules (ROH) without enough perturbation of electronic charges for the reaction to proceed further. The reactions of metal tetrachlorides MCU (M = Ti, Zr, Th) towards ethyl alcohol show a gradation TiCU > Z1CI4 > ThCLj. ... 

Siddiqi et al. (109) prepared a number of tetrakis(dithiocarbamate) complexes, [M(S2CNHR)4] (M = Ti, Zr), derived from primary amines. These can be accessed from the reaction of the pre-formed dithiocarbamate salt, as is the case for propanediamine dithiocarbamate complexes (R = CH2CH2CH2NH2), or from their in situ generation in the presence of the metal tetrachloride (R = A -phenyl-a-naphthylamines, 2-amino-benzothiazole, benzidine, 2,4-tolylene-diamine) (616). 

Chloroform and carbon tetrachloride must not be heated with metallic sodium as an explosive reaction is likely to take place (see footnote, p. 321). 

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