Cyclopentadienide complexes

Tricyclopentadienide complexes of many of the actinides are known (Ac = Th, U, Pu, Am, Cm, Bk, Cf). Indeed, these are the only cyclopentadienide complexes known for the transplutonium elements, where -(-3 is the most stable oxidation state. The transplutonium elements were all prepared by a microchemical procedure which utilized a melt of biscyclopentadienyl beryllium (6) according to ... 

The tris cyclopentadienide complex of uranium was first prepared by the direct reaction of uranium trichloride with a benzene suspension of potassium cyclopentadienide. More recently it has been prepared by the reduction of tetra-... 

Although no single crystal X-ray work has been done on the cyclopentadienide complexes of the trivalent actinides, it is clear that they have structures similar to those of the known homologous lanthanides. Both the trivalent lanthanides and actinides behave as Lewis acids and form adducts to complete their coordination spheres. An optimum formal coordination number of ten is indicated and their structures seem to be dictated by a maximization of electrostatic interactions within the steric constraints of the ligands. 

Table 3. Summary of crystal and molecular parameters for actinide(IV) ji-cyclopentadienide complexes...

Scheme 10.6 Formation of a cyclopentadienide complex of a Qo derivative with Tl.

Evans, W.J., Deming, T.J., and Ziller, J.W. (1989) The utility of ceric ammonium nitrate-derived alkoxide complexes in the synthesis of organometallic cerium(lV) complexes. Synthesis and first X-ray crystallographic determination of a tetravalent cerium cyclopentadienide complex, (C5H5)3Ce(OCMe3). Organometallics, 8, 1581. 

A useful alternative to phosphorus ylids are the titanium reagents, such as, 71, prepared from dicyclopentadienyltitanium dichloride and trimethylaluminum. Treatment of a carbonyl compound with the titanium cyclopentadienide complex 71 Tebbe s reagent) in toluene-THF containing a small amount of pyridine " leads to the alkene. Dimethyltitanocene (Me2TiCp2), called the Petasis reagent, is a convenient and highly useful alternative to The mechanism of Petasis... 

Jacquot de RouviUe H-P, ViUenave D, Rapenne G. Synthesis of a photoswitchable azobenzene-fiinctionalized tris(indazol-l-yl)borate ligand and its ruthenium(II) cyclopentadienide complex. Tetrahedron. 2010 66 1885-1891. 

There are no reports of the use of iridium cyclopentadienide complexes with tritiated water. Such applications would be expected to have disadvantages similar to RhCl3-3H20 and related systems (Section 3.4.1) in terms of specific activity limits and the possibility of thermal decomposition of substrates, but with the additional uncertainty of its applicability to a range of substrate structures and functions. 

Figure 3.58 Structure of active iridium cyclopentadienide complex regioselectivity of deuterium labeling in model substrates...

Figure 3.59 Application of iridium cyclopentadienide complex-mediated deuterium labeling of more complex substrates...

The latter procedure (involving isolation of the organoiridium-substrate complex) is not practical for use in the tritiation of most substrates, but the former may be if deactivation of the complex by polar functional groups is avoided. The regioselectivity that these iridium cyclopentadienide complexes display is largely complementary to those of iridium phosphines and iridium dionates therefore cyclopentadienide complexes could be valuable additions to the repertory. Unfortunately the air-sensitivity of these complexes and their immediate precursors is a hindrance to their use. Further development of this class would be highly desirable. 

Meanwhile, iridium cyclopentadienide complexes have been found to be catalytic in their mediation of exchange of deuterium from H20 (see Section 3.4). 

Hydrocarbon ligands which formally contribute five electrons when bonding to a metal are called Dienyl ligands. Five-electron systems are found for cyclic 5-, 6- and 7-membered hydrocarbon ligands and non-cyclic ligands. The 7r-cyclopentadienyl group is the commonest ligand in this class and the chemistry of cyclopentadenyl metal complexes is discussed first. For convenience, the transition metal cyclopentadienide complexes are also discussed in this section. 

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