Though simple half-sandwiched complexes of Zr(III) and
Hf(III) are known [34], such metal centres are better kinetically stabilised
by bulky ligands as seen from the examples of zirconium(II)
[35] and hafnium(III) [36] below (Fig. 4), synthesised by reducing
the parent chloride with Mg (former) and KC8 (latter).