C5B Ring Double-decker Sandwiches

The activity of CMe2-bridged Zr(II) and Hf(II) boratabenzene cationic complexes toward ethylene trimerization has been explored computationally using a gradient-corrected DFT approach the Zr species was calculated to be a highly efficient catalyst, exceeding the efficiency of the corresponding Cp system.108 

Constrained-geometry catalysts for C2H4 polymerization 88 that are counterparts of well-known ansa-metallocene systems have been prepared and shown to be active, in combination with MAO, toward polymerization of ethylene the product is almost entirely polyethylene, with ca. 1% of 1-octene obtained. The titanium complex was found to be four times as active as the zirconium species.1 

Late transition metal boratabenzene complexes can catalyze C-H activation thus, the bis(ethylene)rhodium derivatives (HsCsB-R)Rh(C2H4)2 (R = Ph, NMe2) promote boration of alkanes faster than does the Cp analog Cp Rh(C2H4)2, although the boratabenzene compounds are thermally less stable.110 

The bis(trimethylphosphino)zirconium complex 92 undergoes unusual reactions with alkynes.114 With diynes, metallocyclic products 93 are formed, whereas acetylene affords 94 whose nonplanar boratanaphthalene ligand is 

Metal complexes of pinene-fused boratabenzene ligands, analogous to chiral metallocenes that have found application in catalysis and enantioselective synthesis, have been prepared.122-124 With late transition metals such as Mn and Fe, the complexes are obtained as mixtures of diastereomers (e.g., 97) with the sterically less congested exo form predominating, but the bis(ligand) Zr complex 98 was obtained as the pure exo,exo product.124 A lithium 

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