Md. Fryzuk et al., Synthesis and structure of the hafnium alkylidene complex [P2Cp]Hf=CHPh(Cl) ([P2Cp] = (eta(5)-C5H3-1,3-(SiMe2CH2PPr2i)(2))), ORGANOMETAL, 20(8), 2001, pp. 1608-1613
The synthesis, structural characterization, and solution behavior of hafniu
m complexes stabilized by the potentially tridentate ancillary ligand [P2Cp
] ([P2Cp] = (eta (5)-C5H3-1,3-(SiMe2CH2PPr2i)(2))) are described. The react
ion of [P2Cp]Li with HfCl4(THT)(2) produces the hafnium trichloride complex
[P2Cp]HfCl3 (1), the structure of which was determined by X-ray crystallog
raphy. Trichloride 1 is isostructural with the analogous zirconium complex
[P2Cp]ZrCl3 (2) in the solid state, but in solution 1 exists as an equilibr
ium mixture of two isomers that interconvert by fluxional phosphine coordin
ation. Treatment of 1 with 2 equiv of KCH2Ph, followed by thermolysis, yiel
ds the first structurally characterized hafnium alkylidene complex, [P2Cp]H
f=CHPh(Cl) (3). A crystal structure determination obtained for 3 shows this
complex to be isostructural with the zirconium analogue [P2Cp]Zr=CHR(Cl) (
4). The primary difference between the Hf systems presented here and the pr
eviously studied Zr analogues is that metal-ligand bonding is stronger in t
he former, which accounts for shorter bond distances, a greater degree of c
hemically inertness, and the divergent solution behaviors observed for the
trichloride derivatives 1 and 2.