A STRUCTURALLY DISTORTED LIGAND IN AN ELECTRON-DEFICIENT DIZIRCONOCENE CATION - UNUSUAL 1,2-DIMETALLIOALKENES AND 1,1-DIMETALLIOALKENES

The selective formation of the catalytically inert complexes 1 and 2 from the potential catalyst system "[Cp2ZrMe]+"/[Cp2ZrMe2] and RC = CH shows how sensitive the catalytic oligomerization of alkynes is to changes in the steric bulk of the substituents at the alkyne and at the Cp ligand of the catalyst (the sterically more crowded [(C5Me5)2ZrMe]+ does catalyze this oligomerization). On account of the electron deficiency at the Zr centers, the MeCCtBu ligand in 1 is strongly distorted, and the alkynyl ligand is more strongly bound to the Zr atom that shows an agostic interaction with the methyl group; in the contrast the alkenylidene ligand in 2 bridges symmetrically.