Cyclopentadienyl complexes with group 15 elements

O-functionalized cyclopentadienyl ligands with these elements in the -LIII oxidation state are abundant. In fact, such complexes form the largest group of compounds in this review. 

P. Jutzi - Cyclopentadienyl Complexes with Main-Group Elements as Central Atoms, /. Organomet. Chem. 400,1, 1990 The Versatility of the Pentamethylcyclopentadienyl Ligand in Main-Group Chemistry,... 

Jutzi P (1990) Cyclopentadienyl complexes with main group elements as central atoms—a decade of research. J Organomet Chem 400 1-17... 

Beryllium forms a series of cyclopentadienyl complexes [Beftj -CsHiY] with Y = H, Cl, Br, Me, —C=CH and BH4, all of which show the expected C5, symmetry (Fig. 5.10a). If the pe/ifo/topfo-cyclopentadienyl group (p. 937) contributes 5 electrons to the bonding, then these are all 8-electron Be complexes consistent with the octet rule for elements of the first short... 

Group 6 alkylidyne poly(pyrazolyl)borate and cyclopentadienyl complexes L M = CR generate dichalcocarboxylates L M(k -A2CR) with elemental chalcogens. The complexes TpMo( = CR)(CO)2, however, fail to react with tellurium and this is attributed to a kinetic phenomenon." The sequential treatment of W( = CR)Br(CO)4 (R = C6H4Me-4) with sulfur and K[Tp] provides TpW... 

Powder as well as MAS studies are available for several r/ -bonded olefins. The spans of the chemical-shift tensors are reduced with respect to the free olefins, which is discussed in terms of the Dewar-Chatt-Duncanson model of fx-donation and tt- back-bonding." " " The bond lengths and the orientations of the shielding tensor elements are available from dipolar-chemical shift methods and 2-D spin-echo experiments on the doubly labelled oleflns." " 77 -cyclopentadienyl and 77 -benzene ligands of transition-metal complexes, but also some derivatives of alkali or main-group elements," exhibit single resonances and shielding tensors of axial symmetry at room temperature. Both observations point to relatively fast rotations around the respective 5- and 6-fold local rotor axis. ... 

The vanadium group element homoleptic compounds with uM —C bonds are relatively thermally unstable and very sensitive to oxidizing agents and water. They also have the tendency to expand the coordination number as a result of R" or Lewis base (amine, phosphine, etc.) addition. Heteroleptic complexes possessing cyclopentadienyl, halogen, 0x0, acetylacetonate, etc., ligands are usually more thermally stable than homoleptic complexes such as MR4. 

The bonding in cyclopentadienylsodium, CjHjNa, is generally regarded as ionic in character. The CgH ion has six 7r-electrons and according to Hiickers 4rH- 2 rule is aromatic. Considerable covalent character, however, probably exists in cyclopentadienyl derivatives of the elements of Groups II, III and IV. The cyclopentadienyl group exhibits a variety of bonding modes which may be compared with those found in transition metal complexes (p. 278). 

The cyclopentadienyl group, C5H5, forms complexes with all the d-block transition elements. Its usual mode of bonding is fy , although there are examples of and f] attachment. In the following series of compounds the 18-electron configuration of the metal is maintained by variation of the number of electrons provided by one of the cyclopentadienyls (Fig. 9.1). 

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