Lanthanoids organometallic compounds

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. 

Organometallic compounds of the early transition elements, especially of the lanthanoides and actinoides, are among the very newest organometallic compounds. The electronically unsaturated character of these elements originally made it very difficult to synthesize satisfactorily stable compounds with metal-to carbon bonds. 

The first indications of the existence of organometallic compounds of the lanthanoides was furnished in the observation that methyl radicals do react with lanthanum metal (l). The publication of the successful syntheses of Sc(C2Hs)3 and Y(C2H5)3 (2), the first supposed alkyl derivatives of the rare earth metals, however, proved to be wrong (3). Also, all attempts to prepare the first phenyl derivatives of lanthanum, carried out by Gilman and coworkers in connection with the separation of... 

With respect to the synthesis of organometallic compounds of the lanthanoides with n -bonded organyls, the cyclopentadienyllanthanoide halides take a key position. The first dicyclopentadienyllanthanoide chlorides were obtained by the reaction of LnCl3 with only two equivalents of NaC5H5, or by redistribution of LnCl3 and Ln(C5H5)3 (42) ... 

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. 

Later Schumann and coworkers using the method, which they have offered previously, have obtained the organometallic compounds of lanthanoids with a Lu-Si bond [5, 6, 7] ... 

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). 

The simplest homoleptic organometallic derivatives of the lanthanoides in the oxidation state Ln " " are the compounds Ln(CH3)3. The driving force for the inner transition elements to achieve high coordination numbers forcasts a high reactivity for these compounds. Thus, for a long time, only indirect evidence could be found for the existence of such derivatives, and the isolation and characterization of compounds belonging to this class was not possible before the last decade. 

With the successful synthesis of quite a respectable number of organo-metallic compounds of the lanthanoides in the last 15 years, one of the last gaps in the organometallic chemistry is filled, although timidly. 

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... 

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