Complexation of Bis(trimethylsilyl)acetylene by Decamethylhafnocene To Give the Hafnacyclopropene Cp*2Hf(η2-Me3SiC2SiMe3): An Unusually Strong Metal−Alkyne Interaction

The complexes Cp 2 Hf(PMe 3 )(η 2 -Me 3 SiC 2 SiMe 3 ) ( 3 ) and Cp* 2 Hf(η 2 -Me 3 SiC 2 SiMe 3 ) ( 4 ), as the first examples of well-defined hafnium alkyne complexes with a simple intact alkyne, are described; 4 displays an unusually strong interaction of the alkyne with hafnium, in comparison to analogous compounds of titanium and zirconium.