Trimethylphosphine halide complexes of titanium, zirconium and hafnium in oxidation states IV, III and II. Crystal structure of MI4(PMe3)n (M=Zr, n=3; M=Hf, n=2.5), M2X6(PMe3)4 (M=Hf, Ti, X=I; M=Zr, X=Br) and (μ-η6,η6-C6H6)Hf2I4(PMe3)4·C6H6

The reaction of MI4 (M=Zr, Hf) with trimethylphosphine in benzene solution leads to different compounds, ZrI4(PMe3)3 (1) and HfI4(PMe3)2.5 (2), According to the single-crystal X-ray diffraction study, Zr in 1 has a capped trigonal antiprismatic coordination by four I and three P atoms. Superposition of two molecules, HfI4(PMe3)3 and HfI4(PMe3)2 in 1:1 ratio has been found in 2. The reduction of MX4 with 1 equiv. of Na/Hg amalgam in the presence of PMe3 afforded bioctahedral M(III) complexes Hf2I6(PMe3)4 (3), Zr2Br6(PMe3)4 (4) and Ti2I6(PMe3)4 (5). The compounds 3 and 4 are characterized by a cis-cis arrangement of phosphine ligands with respect to two M centres with direct M∙∙∙M bonds at distances of 3.33 Å (3) and 3.20 Å (4). There is no Ti-Ti bond in the cis-trans complex 5 with the Ti∙∙∙Ti distance of 4.30 Å. The reduction of HfI4 with 2 equiv. of Na/Hg amalgam in the presence of PMe3 resulted in the isolation of Hf(II) complex, (μ-η6,η6-C6H6)Hf2I4(PMe3)4∙C6H6 (6). The complex 6 contains dinuclear molecules with two-sided coordination of benzene by two Hf atoms. The strong deformation of coordinated benzene in the form of a twisted boat (C-C 1.45-1.46 Å) is explained by steric repulsion from the neighbouring PMe3 ligands