Synthesis and Structure of the Hafnium Alkylidene Complex [P2Cp]HfCHPh(Cl) ([P2Cp] = (η5-C5H3-1,3-(SiMe2CH2PPri2)2))

The synthesis, structural characterization, and solution behavior of hafnium complexes stabilized by the potentially tridentate ancillary ligand [P 2 Cp] ([P 2 Cp] = (η 5 -C 5 H 3 -1,3-(SiMe 2 CH 2 PPr i 2 ) 2 )) are described. The reaction of [P 2 Cp]Li with HfCl 4 (THT) 2 produces the hafnium trichloride complex [P 2 Cp]HfCl 3 ( 1 ), the structure of which was determined by X-ray crystallography. Trichloride 1 is isostructural with the analogous zirconium complex [P 2 Cp]ZrCl 3 ( 2 ) in the solid state, but in solution 1 exists as an equilibrium mixture of two isomers that interconvert by fluxional phosphine coordination. Treatment of 1 with 2 equiv of KCH 2 Ph, followed by thermolysis, yields the first structurally characterized hafnium alkylidene complex, [P 2 Cp]Hf CHPh(Cl) ( 3 ). A crystal structure determination obtained for 3 shows this complex to be isostructural with the zirconium analogue [P 2 Cp]Zr CHR(Cl) ( 4 ). The primary difference between the Hf systems presented here and the previously studied Zr analogues is that metal−ligand bonding is stronger in the former, which accounts for shorter bond distances, a greater degree of chemically inertness, and the divergent solution behaviors observed for the trichloride derivatives 1 and 2 .