Lanthanides, organometallic compounds

Compounds of these metals involving either a- or tt-bonds to carbon are generally much more reactive to both air and water than those of the d-block metals. Thus there is no lanthanide equivalent of ferrocene, an unreactive air- and heat-stable compound. They are often thermally stable to 100 °C or more, but are usually decomposed immediately by air (and are not infrequently pyrophoric). Within these limitations, lanthanide organometallic compounds have their own special features, often linked with the large size of these metals. 

Although the first lanthanide organometallic compounds were reported only three years after the discovery of ferrocene (Birmingham and Wilkinson, 1956), the years until 1968 saw only limited interest in this area. However, after the suggestion in that year that there is f orbital involvement in uranocene (Streit-wieser, Jr. and Mtiller-Westerhoff, 1968), there has been a notable resurgence of interest in these complexes. The field has been surveyed in two comprehensive reviews (Hayes and Thomas, 1971 Kanellakopulos and Bagnall, 1972) and each year there is a summary of the reported research in the Journal of Organometallic Chemistry. 

The organic hgands of the actinide and lanthanide organometallics will be used here as an arbitrary basis of classification. The emphasis will be on the structure and bonding of these compounds rather than their S5uithetic chemistry. Several earher reviews exist which cover the chemical aspects of the organoactinides and -lanthanides [1—7). 

The first weU-characterized organometallic compounds of the lanthanides or actinides were the tricyclopentadienides of various lanthanide ions S3mthesized by Birmingham and Wilkinson in 1954 (97—98). Anhydrous metal chlorides were reacted with sodium cyclopentadienide in tetrahydrofuran as follows ... 

Organometallic Compounds of the Lanthanides, Actinides, and Early Transition Metals. (Edit. Cardin, D.J.). Chapman Hall London, 1985. 

Synthetic routes include anionic, cationic, zwitterionic, and coordination polymerization. A wide range of organometallic compounds has been proven as effective initiators/catalysts for ROP of lactones Lewis acids (e.g., A1C13, BF3, and ZnCl2) [150], alkali metal compounds [160], organozinc compounds [161], tin compounds of which stannous octoate [also referred to as stannous-2-ethylhexanoate or tin(II) octoate] is the most well known [162-164], organo-acid rare earth compounds such as lanthanide complexes [165-168], and aluminum alkoxides [169]. Stannous-2-ethylhexanoate is one of the most extensively used initiators for the coordination polymerization of biomaterials, thanks to the ease of polymerization and because it has been approved by the FDA [170]. 

Some of the applications of the organometallic compounds of lanthanides are as catalysts for (i) stereo specific polymerization of diolefins and in particular to obtain high yields of 1,4-ci.v-polybutadiene and 1,4-cw-polyisoprene and copolymer of the two monomers. The order of effectiveness of the rare earths as catalysts is Nd > Ce, Pr < Sm, Eu. The nature of halogen of the Lewis acid affecting the catalytic activity is in the order Br > Cl > I > F. Detailed work on the activity of cerium octanoate-AlR3-halide showed stereo specificity with cerium as the primary regulator. Cerium is thought to form jr-allyl or 7r-crotyl complexes with butadiene. 

Organometallic compounds of the lanthanides in the oxidation state Ln(II) were first reported in the early 1980s... 

Organometallic compounds of lanthanide metals other than Sm, Eu, and Yb are very rare until now. But the development of this chemistry became possible after the synthesis of divalent precursors of Tm, Dy, and Nd in the late 1990s, namely of their diiodides (see Scandium, Yttrium the Lanthanides Inorganic Coordination Chemistry) and by using hgands such as phospholyl or arsolyl, which stabilize divalent lanthanide ions. 

It should be noted that there are organometallic compounds involving polyhapto ligands that contain linkages such as Sc— Te that are not found in coordination compounds. In addition, a number of recent reviews on the organometallic chemistry of the lanthanides include reference to scandium compounds. ... 

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