Lanthanides organolanthanide complexes

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

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). 

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-... 

The first report on organolanthanide-promoted Tishchenko reactions, that is, the transformation of aldehydes or mixed aldehydes into the corresponding esters, including a mechanistic proposal appeared in 1996 [catalyst Cp2 LnCH(SiMe3)2 with Ln = La and Nd] [233]. Two years later, lanthanide silylamide complexes Ln[N(SiMe3)2]3 were found as easily accessible and even more active catalysts (Scheme 12.24) [234, 235]. 

Anwander R (1996) Routes to Monomeric Lanthanide Alkoxides. 179 149-246 Anwander R, Herrmann WA (1996) Features of Organolanthanide Complexes. 179 1-32 Artymiuk PJ, Poirette AR, Rice DW, Willett P (1995) The Use of Graph Theoretical Methods for the Comparison of the Structures of Biological Macromolecules. 174 73-104 Astruc D (1991) The Use of p-Organoiron Sandwiches in Aromatic Chemistry. 160 47-96 Baerends EJ, see van Leeuwen R (1996) 180 107-168 Balbds LC, see Alonso JA (1996) 182 119-171... 

Organolanthanide complexes are coordinately unsaturated and as a result take part in forming mixed complexes with transition metal complexes containing nitrosyl or carbonyl groups. As a result, mixed complexes containing metal-metal bonds or lanthanide-isocarbonyl or isonitrosyl interactions have been characterized. Some typical complexes are given below. 

A number of organolanthanide complexes with carbo-ranes either bonded to the lanthanide metals via one carbon atom or with an open side as Cp analogs have been... 

Since the chemistry of organolanthanide complexes is rather invariant to the number of 4/ electrons, a metal of similar size and charge but with no/ electrons could have similar chemical properties. Such is the case for yttrium and it will be included in this article. Although yttrium is not formally a lanthanide element, it is congeneric with lanthanum. More importantly, the radial size of the trivalent yttrium ion is nearly identical with that of Er. As such, its chemistry, at least so far, has proven to be very similar to that of the late lanthanides. Since is diamagnetic (cf. Er, - 9.4-9.7 B.M.) with I = j, it provides NMR-accessible... 

The properties of the lanthanide elements and their organometallic complexes described in the previous section explain in part why organo-met lic chemists in the past found lanthanide chemistry much less interesting than transition metal chemistry. The highly ionic, trivalent organolanthanide complexes appeared to have little potential to interact with the small-molecule substrates that provide such a rich chemistry for the transition metals neutral unsaturated hydrocarbons, H2, CO, phosphines, etc. The two-electron oxidation reduction cycles so important in catalytic transition metal chemistry in 18 16 electron complexes seemed... 

The classical divalent organolanthanide complexes, mainly for Sm + and Yb +, have strong reducing potentials. They can reduce a series of transition metal carbonyls and AgBPh4 to give the cationic lanthanide complexes. 

A metathesis reaction is a convenient route to lanthanide tetrahydroaluminate and lanthanide tetrahydroborate complexes. Using tetrahydroaluminate complexes as the hydride source, a number of structurally characterized lanthanide tetrahydroaluminate complexes are prepared via metathesis reactions in the presence of an excess of a Lewis base (Equation 8.24) [79]. Metathesis reaction of organolanthanide chlorides with alkali metal tetrahydroborate generates the corresponding lanthanide tetrahydroborate. The same reaction with sodium hydride in THE is reported to afford a lanthanide hydride however, no molecular structure for the hydride has been presented up till now. 

Divalent lanthanide chemistry has been dominated by the most readily accessible divalent lanthanide metals samarium(II), europium(II), and ytterbium(II) (classical ) for decades, and a large number of divalent lanthanide compounds have been prepared [92], There are three routes to generate divalent organolanthanide complexes oxidative reaction of lanthanide metal, metathesis reaction of a divalent lanthanide halide, and reductive reaction of a trivalent lanthanide complex. 

Transmetallation is a more convenient method to obtaining divalent organolanthanide complexes from lanthanide metals. Reaction of lanthanide metal powder with a mercury alkyl or aryl complex affords the corresponding divalent lanthanide complex (Equation 8.28) [94]. The preparation of divalent perfluorophenyl lanthanide complexes Ln(C6F5)2(THF) (Ln = Eu, n = 5 Ln = Yb, n=4) is a typical example. In most cases, the addition of a small amount of Lnl3 leads to acceleration of the reaction [95]. 

An alternative route to divalent lanthanide complexes is a metallation reaction the acid-base reaction between a divalent organolanthanide complex with an acidic substrate... 

The non-classical divalent lanthanide complexes have stronger reducing power than divalent samarium complexes because of their higher reduction potentials. Dinitrogen is not an inert atmosphere for these non-classical divalent lanthanide complexes. Therefore, attempts to prepare non-classical divalent organolanthanide complexes by metathesis reactions in dinitrogen atmosphere have been unsuccessful, and the dinitrogen-activated products were isolated. A typical example is shown in Equation 8.36 [112]. 

Because the 5d orbitals of lanthanide metals are shielded by 4f orbitals, the lanthanide metals cannot effectively back-bond like the transition metals, and the alkynes and the CO are expected to have no significant chemistry with organolanthanide complexes. However, the divalent samarium complex (C5Me5)2Sm(THF)2 can reduce diphenyl ethyne, and subsequently activate CO to generate a tetracyclic compound, as shown in Figure 8.33 [113]. 

Divalent organolanthanide complexes can also initiate MMA polymerization. A divalent lanthanide complex, as a single-electron transfer reagent, can readily react with the monomer to generate a radical anion species, which subsequently couples into a bimetallic trivalent lanthanide enolate intermediate, which is the active center. Therefore, divalent organolanthanide complexes serve as bisinitiators for MMA polymerization [160]. 

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