A Stable Schrock-Type Hafnium−Silylene Complex

The first stable hafnium−silylene complex, (η-C5H4Et)2(PMe3)HfSi(SiMetBu2)2 (6) was obtained in the form of the phosphine adduct as red crystals by the coupling reaction of 1,1-dilithiosilane (1) with 0.9 equiv of (η-C5H4Et)2HfCl2 in dry toluene at −50 °C, followed by treatment with an excess of PMe3 at −50 °C. In the 29Si NMR spectrum of 6, the signal from the silylene ligand is shifted greatly downfield at 295.4 ppm, with a JSiP coupling constant of 15.0 Hz. X-ray crystallographic analysis of 6 revealed that the Si−Hf bond length (2.6515(9) Å) is about 5% shorter than typical Si−Hf single bonds, obviously indicating the double-bond character between the silicon and hafnium atoms. The compound 6 was found to be a Schrock-type silylene complex, a conclusion that was supported by the natural population analysis (NPA) charge distribution for the model complex, (η-C5H4Et)2(PMe3)HfSi(SiMe3)2 (8), showing a negative charge on the silicon atom (−0.34).