Fluorenyl derivatives of early transition elements: a synthetic and structural study

The tetracarbonyls of niobium(I) and tantalum(I), M(eta (5)-9-phenylfluoren yl)(CO)(4), have been prepared from the dinuclear tetracarbonyl anions [M-2 (mu -Cl)(3)(CO)(8)](-) and Li(9-phenylfluorenyl). A slightly distorted four -legged piano stool geometry, due to the presence of the sterically demandi ng phenyl substituent, has been found in the case of the niobium derivative . The crystal and molecular structures of Zr(fluorenyl)(2)Me-2 and of the 9 -phenyl-substituted derivative have been solved. The structure of Zr(fluore nyl)(2)Me-2 is similar to that of the known dichloride, Zr(fluorenyl)(2)Cl- 2 where fluorenyl ligands of different hapticity are present. On the other hand, the use of the more sterically demanding phenyl-substituted fluorenyl ligand in Zr(eta (5)-9-phenylfluorenyl)(2)Me-2, induces the fluorenyl liga nds to be symmetrically and pentahapto-coordinated to zirconium. (C) 2001 E lsevier Science B.V. All rights reserved.