Organometallic complexes of the lanthanoids

Despite the extreme air and moisture sensitivity of organo-lanthanoid compounds, this is a rapidly expanding research area. An exciting aspect of organolanthanoid chemistry is the number of efficient catalysts for organic transformations that have been discovered (see Box 25.5). In contrast to the extensive carbonyl chemistry of the J-block metals (see Sections 24.4 and 24.9), lanthanoid metals do not form complexes with CO under normal conditions. Unstable carbonyls such as Nd(CO)g have been prepared by matrix isolation. Since organolanthanoids are usually air- and moisture-sensitive and may be pyrophoric, handling the compounds under inert atmospheres is essential.  

Lower coordination numbers can be stabilized by using aryloxy or amido ligands, for example  

In the solid state, [Nd N(SiMe3)2 3] is trigonal pyramidal but this may be a consequence of crystal packing forces (see Section 19.7). 

Organolanthanoid chemistry is a rapidly expanding research area, and an exciting aspect of this area is the number of efficient catalysts for organic transformations that have been discovered (see Box 24.5). In contrast to the extensive carbonyl chemistry of the d -block metals (see Sections 

4 and 23.9), lanthanoid metals do not form complexes with CO under normal conditions. Unstable carbonyls such as Nd(CO)5 have been prepared by matrix isolation. Organolanthanoids are usually air- and moisture-sensitive and some are pyrophoric handling the compounds under inert atmospheres is essential.  

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Give a short account of aspects of the organometallic compounds formed by the lanthanoids and actinoids and highlight major differences between families of organometallic complexes of the d- and /-block metals. 

The coordination and organometallic chemistries of the lanthanoid metals are rapidly growing areas of research. Since most complexes are paramagnetic, routine characterization by NMR spectroscopic methods is not usually possible. Thus, compound characterization tends to rely on X-ray diffraction studies. The paramagnetic nature of lanthanoid complexes has, however, been turned to advantage in their application as NMR shift reagents (Box 25.4) and MRI contrast agents (Box 3.6). 

Zeimentz, P.M., Arndt, S., Elvidge, B.R. etal. (2006) Cationic organometallic complexes of scandium, yttrium, and the lanthanoids. Chemical Reviews, 106, 2404. 

In I96U, the blue solution of metallic europium in liquid ammonia was found to react with cyclopentadiene. The sublimation of the crude product at U00 C in vacuo yields an ammonia-free syndwich complex, as the first organometallic compound of a lanthanoide in the oxidation state Ln (183). The ytterbiinn complex has been prepared in a similar manner (15) ... 

Typical ligands for the organometallic compounds of the transition metals in low oxidation states are CO and the olefins. Therefore, no experiment has been left undone to synthesize such carbonyl or olefin complexes of the elements of the third subgroup and of the lanthanoides. Whereas lanthanoide carbonyls could be detected only in a matrix until now (213), the first indications have been obtained for the existence of olefin complexes. 

Other relevant material is contained in reviews on homogeneous catalysis of organic reactions by transition metal complexes, highly reduced metal carbonyl complexes, phosphine complexes of the early transition metal complexes and the lanthanoids, metal NMR spectra of transition metal organometallic systems, the coordination chemistry of C-Nitroso-compounds, mono-Cp halide complexes of the d- and/-block, and organometallic chemistry in the gas phase. o... 

In the first of these techniques the lanthanoid complex (33) (5-8 mol%) is used as the organometallic activator in cumene hydroperoxide or tert-butyl hydrogen peroxide-mediated oxidation of chalcone (epoxide yield 99 % 99 % ee) or the ketone (34) (Scheme 20)[1001. 

The benzoyl peroxide, as a rule, easily splits off all metal-metal bonds in polynuclear organometallics [32]. In contrast, the tin-praseodymium complex in the reaction with (PhCOO)2 retains one Sn-Pr group. The formed heteroleptic product (Me3SiCH2)3SnPr-(OCOPh)2 belongs to the group of rare air-stable organoelement derivatives of lanthanoids. 

The organometallic chemistry of lanthanoids is dominated by cyclopentadie-nyl-derivatives as ligands. Indenyl and fluorenyl-substituted NHCs, however, were only recently introduced to this chemistry. The group of Cui published a series of indenyl (40) and fluorenyl (41) NHC complexes (Figure 6.6) by deprotonating the imidazolium bromide precursor with [Li(CH2SiMc3)] and... 

Shibasaki, M. and Groger, H. (1999) Chiral heterobimetallic lanthanoid complexes highly efficient multifunctional catalysts for the asymmetric formation of CC CO and CP bonds. Topics in Organometallic Chemistry, 2 (Lanthanides) 199-232. 

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