Cyclopentadienyls- lanthanides with

A variety of the metal-metal bonded complexes or clusters also provide a foothold for the studies of f-orbital participation. Examples of such organo-lanthanide complexes include cyclopentadienyl lanthanides with lanthanide-to-transition metal bonding L(n -C H ) LnW (n -C H )(CO), (n -C H.) LnMo(n --C H )... 

An approach other than steric hindrance has been used to overcome the previously mentioned instability of the actinide homoalkyls. It was found that the inclusion of jT-bonding ligands in the coordination sphere considerably enhanced the stability of the alkyl complex. Recently, the same line of reasoning has also yielded a new series of 7r-cyclopentadienyl lanthanide alkyls (C5H5)2LnR where Ln =Gd, Er, Yb and R = C=C, and CH3 120,121). The infrared data for these complexes are consistent with u-bonded structures and the room temperature magnetic susceptibilities are very close to the free ion values. The actinide complexes (75,... 

The homoleptic lanthanide(III) benzamidinates 20-23 can be regarded as analogues of the well known tris(cyclopentadienyl)lanthanide complexes (C5H5)3Ln [7, 8]. One of the most characteristic reactions of the homoleptic cyclopentadienyls is the formation of 1 1 adducts with Lewis bases such as ethers, nitriles, esters etc. [7, 8], Recently it was discovered that the homoleptic lanthanide benzamidinates [PhC(NSiMe3)2]3Ln (20) form similar adducts with THF and nitrile ligands such as acetonitrile or benzonitrile [59]. The molecular and crystal structures of two benzonitrile adducts (26g, h) have been determined by X-ray diffraction. Figure 8 depicts the molecular structure of the europium... 

The properties of cyclopentadienyl lanthanide compounds are influenced markedly by the relationship between the size of the lanthanide atoms and the steric demand of the Cp group. The former varies from La to Lu according to lanthanide contraction, while the latter varies from the least bulky Cp to highly substituted Cp, which is appreciably larger. The Sc and Y complexes are very similar to those of lanthanides with proper allowance for the relative atomic sizes. 

Adducts [Ln(CsH5)3(THF)] exist for all lanthanides. They have ten-coordinate lanthanides with three -cyclopentadienyl rings and a monodentate THF, having pseudo-tetrahedral geometry round the lanthanide (Figure 6.7). They are one of those rare cases when the same coordination number is maintained across the lanthanide series. 

Tris(cyclopentadienyl)lanthanide complexes with steri-cally more crowded Cp ligands such as C5Me4R (R = Me, Et, Tr, and SiMe3) are not assessable by simple metathesis between lanthanide trihalides and the respective alkali metal salt of the bulky Cp ligand. For instance, Cp 3Sm, obtainable from Cp 2Sm and cyclooctatetraene, reacts with THF with ring-opening forming Cp 2Sm[0(CH2)4Cp ](THF) (equation 14). 

The organometalhc chemistry of the rare earths deals mainly with bis(cyclopentadienyl) derivatives due to the easy available bis(cyclopentadienyl) rare earth chlorides and other halides via reaction of the rare earth trichlorides with two equivalents of a cyclopentadienyl alkali salt. Bis(cyclopentadienyl)lanthanide chlorides are formed as chloride-bridged dimers (Figure 28a), as monomers stabihzed by a donor molecule like THF (Figure 28b) or as ate complexes with alkali hahdes (Figure 28c). 

Following the synthesis of tris(cyclopentadienyl) lanthanide complexes, the first examples of organolanthanide derivatives, a vast number of organolanthanide it-complexes with cyclopen-tadienyl (Cp), indenyl (Ind), cyclooctatetraenyl (COT), and related substituted derivatives have been prepared and extensively reviewed [3]. Here we will briefly discuss cyclopentadienyl and allyl derivatives as representatives of organolanthanide K-complexes. 

For a bulky substituted cyclopentadienyl group, such as CsMes and CsMeaR (R = Et, Pr, SiMes), tris(cyclopentadienyl) lanthanide complexes cannot be prepared via the above metathesis reaction because of the steric hindrance. The reaction of anhydrous LnCls with three equivalents of alkali metal pentamethylcyclopentadienyl in THF (tetrahydrofuran) led to the THF ring-opened product (Equation 8.4) [8]. 

Lanthanide monohydride complexes, such as bi(cyclopentadienyl) lanthanide hydrides, can be conveniently prepared by the reactions of lanthanide mono-alkyl or -aryl complexes with organosilanes under mild reaction conditions (Figure 8.27) [82]. 

Both bi(cyclopentadienyl) lanthanide hydrides and tetranuclear lanthanide octahydrides can react with nitriles, resulting in the reduction of the C=N triple bonds. However, the reducing... 

We have found that the late metal congeners of this important compound class are easily synthesized and can be derivatized to yield aryl monocyclo-octatetraene lanthanide complexes if the metal is small (Er—Lu) and the ligand bulky and chelating. The synthesis of these compounds clears the way for comparative reactivity studies (with cyclopentadienyl lanthanide complexes) and allows investigations of fundamental chemical reactivity to be conducted for this ligand system. 

Pendant-arm amido-cyclopentadienyl ligands have also been shown to be useful in the stabilization of highly reactive mono(cyclopentadienyl)lanthanide alkyl and hydrido complexes. When the tris(trimethylsilylmethyl) complexes of lutetium and ytterbium, Ln(CFI2SiMe3)3(TFIF)2, were treated in pentane solution with 1 equiv. of (CsMe4H)SiMe2NHCMe2R (R = Me, Et) at 0°C, the new complexes (rfir)1-... 

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