Cyclopentadienyl chemistry

Reaction of the same neutral borabenzene-ligand adduct, C5H5B-PMe3, with a transition, rather than an alkali, metal alkyl or amide can furnish r 6-boratabenzene complexes in a single step (Scheme 8).17 This efficient transformation presumably proceeds through initial ir-coordination of CsHsB-PMes to the transition metal, followedby an intramolecular substitution reaction. In contrast to other approaches to the synthesis of T 6-boratabenzene complexes, this synthetic route does not have a parallel in if-cyclopentadienyl chemistry. 

The discovery and structural elucidation of ferrocene in 1951 and the subsequent development of metal-cyclopentadienyl chemistry started a new era in organometallic chemistry . 

Monomeric Ce(tritox)3 was claimed in 1989 [29]. However, the structure determination was hampered by disordering problems both in solvent-free Ce(tritox)3 and Nd(tritox)3(THF) [36]. Appropriate crystallization conditions were borrowed from cyclopentadienyl chemistry. The corresponding LnCp3 systems show remarkable crystallization behavior in the presence of neutral bases like acetonitrile and DMSO which impose polarities into the molecule [37], Indeed, this phenomenon could be transferred to Nd(tritox)3 in a 2-phase system n-pentane/acetonitrile at — 35°C [38], X-ray analysis revealed a monomeric alkoxide of formula Nd(tritox)3(NCCH3)2 with a trigonal bipyramidal geometry at the neodymium center (Fig. 2, Table 1). The alkoxide O-atoms and... 

The situation in the cyclopentadienyl chemistry of tin is similar to that described for germanium several classes of cyclopentadienyl compounds are now known. The first compound in this series was reported by Fischer and... 

One of the most fascinating areas of metal-cyclopentadienyl chemistry in recent years concerns the formation and relative stabilities of metal-locenyl-carbonium ions. The ability of iron to stabilize cationic centers in certain ferrocene compounds was noted by Weliky and Gould 243) in 1957. In 1959 Richards and Hill 218y 214, ) reported the results of some kinetic studies relating to the relative rates of solvolysis of metal-locenylmethylcarbinyl acetates. They determined that these solvolyses proceeded via a carbonium ion mechanism and found that the ferrocenyl acetate, for example, solvolyzed nearly seven times faster than did tri-phenylmethyl acetate under the same conditions. 

Cyclopentadienyl chemistry has clearly attained a state of maturity now. This success is in no small part due to the fact that the steric and electronic properties of cyclopentadienyl ligands can be fine-tuned by the judicious choice of substitutents. However, the basic features of these ligands cannot be extended much further this way. 

Thiele, J. Ber. Dtsch. Chem. Ges. 1900, 33, 666. In a recent review on alkali-metal cyclopentadienyl chemistry this paper is erroneously interpreted as reporting the preparation of sodium cyclopentadienide see Harder, S. Coord. Chem. Rev. 1998, 176,... 

From a practical point of view the cyclopentadienyl ligand may be important for several reasons. Clusters can be stabilized with relatively few ligands and these ligands may be capable of changing their mode of coordination. The change in coordination is accompanied by change in the electron donation made to the metal center. In mononuclear-cyclopentadienyl chemistry the conversion of (/j -CsHs) (/j -CsHs) is important in catalytic reactions perhaps conversions of this sort will prove to be important in cluster-cyclopentadienyl chemistry as well. From an aesthetic point of view the symmetry inherent to the (jj -CsHs) ligand in consort with the symmetry of a cluster core makes these compounds particularly attractive. 

Hanusa TP (2002) New developments in the cyclopentadienyl chemistry of the alkaline- earth metals. Organometallics 21 2559-2571... 

The rapid development of cyclopentadienyl chemistry of the early transition metals, lanthanides and actinides is a noteable feature of the 1986 literature. In arene chemistry, further reports of uranium arene complexes and the report of the first lanthanide arene complex confirm that these complexes are isolated examples of an emerging class. 

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