Organolanthanides

The growth of organoactinide chemistry, like that of organolanthanide chemistry, is comparatively... 

A review article entitled "Bulky amido ligands in rare-earth chemistry Syntheses, structures, and catalysis" has been published by Roesky. Benzamidinate ligands are briefly mentioned in this contexD The use of bulky benzamidinate ligands in organolanthanide chemistry was also briefly mentioned in a review article by Okuda et al. devoted to "Cationic alkyl complexes of the rare-earth metals S mthesis, structure, and reactivity." Particularly mentioned in this article are reactions of neutral bis(alkyl) lanthanide benzamidinates with [NMe2HPh][BPh4] which result in the formation of thermally robust ion pairs (Scheme 55). ... 

A new class of organolanthanide complex has been reported from the metal-atom reaction of lanthanide atoms and butadiene (BD) or 2,-... 

Anwander R (1999) Principles in Organolanthanide Chemistry. 2 1-62 Arends IWCE, Kodama T, Sheldon RA (2004) Oxidations Using Ruthenium Catalysts. 11 277-320... 

Although efficient for the intramolecular hydroamination/cyclization (abbreviated IH below) of aminoalkenes (see below), organolanthanides exhibit a much lower catalytic activity for the intermolecular hydroamination of aUcenes, as exemplified by the reaction of n-PrNH2 with 1-pentene catalyzed by a neodymium complex (Eq. 4.17) [127]. 

The efficiency of the more readily accessible Cp 2Sm and Cp 2Sm(thf)2 complexes was also recognized [128, 129[. Further studies indicate that active catalyst precursors include organolanthanide complexes of the general formula Cp 2Ln-R (Ln = La, Nd, Sm, Yh, Lu) with R = H, T),- C5H5, CH(TMS)2, N(TMS)2 [131[. Generation of the catalytically active species is believed to occur via protonolysis of the Ln-R bond by the amine (Eq. 4.19). 

Organolanthanides are catalyst precursors for the formation of five-, six-, and even seven-membered heterocycles. These IHs are also effective with secondary and aromatic amines (e.g. Eq. 4.20). 

Scheme 4-3 Catalytic cycle for the organolanthanide-catalyzed IH of aminoalkenes...

Organolanthanides are effective catalyst precursors for the regioselective hydroami-nation of internal alkynes with primary amines (Eq. 4.80) [127]. 

Organolanthanides are efficient catalyst precursors for the regioselective (>95%) IH of primary aminoalkynes, forming five-, six-, and seven-membered cyclic imines via Exo-Dig processes (Eq. 4.86) [303, 304]. 

Marks and Douglass recently reported organolanthanide-catalyzed hydrophosphina-tion/cyclization of phosphino-alkenes and -alkynes (Scheme 5-15). 

Scheme 5-15 Examples of organolanthanide-cat-alyzed hydrophosphina-tion/q clization. Eq. (6) Phosphinoalkenes can undergo organolanthanide-catalyzed hydrophosphi-nation/cyclization to give phospholanes or an uncatalyzed reaction to give phosphorinanes...

Scheme 5-16 Proposed mechanism of organolanthanide-cat-alyzed hydrophosphination/cyclization...

Metal vapor chemistry showed that the lanthanides had quite an extensive chemistry with unsaturated hydrocarbons. Some of the early surveys of metal vapor reactions with unsaturated hydrocarbons included some lanthanide metals and showed that reactivity was present for these metals (14-18). Subsequent synthetic studies in which the products were isolated and characterized led to some of the most unusual organolanthanide complexes currently known (19-28). 

The metal vapor reaction products differed from traditional organolanthanide complexes in many ways. First, the observed stoichiometries had low ligand to metal ratios. For example, the ytterbium and samarium 3-hexyne products (Reaction 4) had formal ligand to metal ratios of one, whereas most organolanthanides are commonly nine or ten coordinate (6-10). Second, the stoichiometries varied in an... 

Although the structures of these species were not determined, this metal vapor chemistry clearly showed that unsaturated hydrocarbons were viable reagents for lanthanides. Furthermore, this high energy technique showed that new regimes of organolanthanide complexes were accessible under the appropriate conditions. In addition, attempts to understand the synthesis of the products in reac-... 

Analysis of possible structures and reaction pathways in reactions 1-4 led to various model structures for these complexes (9t25). Some of these involved C-H activation of the substituents attached to the unsaturated carbon atoms. To test the validity of these models, two additional types of metal vapor reactions were examined. In one case, reactions with simpler unsubstituted hydrocarbons were examined. In another case, substrates ideally set up for oxidative addition of C-H to the metal center were examined. As described in the following paragraphs, both of these approaches expanded the horizons of organolanthanide chemistry. 

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