Hafnium tetrahalides compounds

Compounds of zirconium and hafnium metal tetrahalides with the bidentate ligands ( )4As2C2H4 and ( )4P2C2H4 were prepared 447) by the reaction of the tetrahalide and the ligand in a suspension in benzene. These are presumably species with a coordination number of eight. The infrared absorption frequencies in the 460-250 cm region are tabulated in Table VII. 

In a recent attempt we have reacted a TMEDA-adduct of tris(trimethylsilyl)silyl potassium with hafnium tetrachloride [8]. This represents the first example of a reaction of a silyl anion with a group 4 tetrahalide. The product obtained is tris(trimethylsilyl)silylhaMum trichloride, with one TMEDA molecule coordinated. With three potential leaving groups still present in the molecule, we hope that it might serve as a useful precursor for a number of differently substituted silyl hafnium compounds. 

The free energies of formation of corresponding hafnium and zirconium compounds are also nearly equal, so that separation by preferential reaction of one species is difficult, too. Table 7.9 compares the free energies of formation of hafnium and zirconium tetrahalides at 1000 K. 

Direct reaction of zirconium and hafnium tetrahalides and bromides with excess DMSO under strictly anhydrous conditions yielded products of composition Zr(Hf)Cl4 9DMSO and Zr(Hf)Br4 lODMSO (482). Attempts to recover the tetrahalides by heating only resulted in the production of tarry residues. The S-O-stretching frequency in these compounds was found to be 960 cm" for the nine-solvate and 920 cm for the 10-solvate, which indicates that the DMSO molecules are oxygen bound. 

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