ion upon treatment with B(C6F5)3 in THF to generate the cationic species [(MAC)Y(CH2SiMe3)][B(C6F5)3(CH2SiMe3)]. However, this salt was found to be highly unstable and could not be isolated as a pure material.97 Fryzuk et al. have developed a remarkable organoyttrium chemistry around the phosphorus-containing macrocycle syn-{P2N2} ({P2N2} ) [PhP(CH2SiMe2NSiMe2CH2)2PPh]). The starting material was the chloride-bridged dimer [{P2N2}Y(μ-Cl)]2, which can be prepared in 95% yield by the reaction of synLi2(THF){P2N2} with YCl3(THF)3 in THF solution. Straightforward metathesis using the very bulky alkyllithium reagent LiCH(SiMe3)2 according to eq 29 (methyl groups on Si omitted for clarity) afforded the monomeric yttrium alkyl species {P2N2}YCH(SiMe3)2 in 92% yield. Use of the less sterically hindered alkyl moiety CH2SiMe3 followed by addition of THF resulted in formation of the THF adduct {P2N2}YCH2SiMe3(THF), whereas the THF-free compound could only be isolated as a highly reactive oily material.98 A quite remarkable samarium alkyl complex of complicated molecular structure was reported by Gambarotta et al.99 Samarium diiodide acted as reducing agent in the reaction with (phenylenebis(3,5-tBu4-salicylidene)iminato)sodium, (3,5tBu4salophen)Na2(THF)3, to give dimeric [Sm2(SBSB)(THF)3]‚2toluene (SB-SB ) C-C bonded 3,5tBu4salophen dimer). The new ligand resulted from the reductive coupling of two imino functional groups of two 3,5-tBu4salophenSm units. Subsequent treatment with MeLi resulted in a novel oxo-bridged dimer (24), featuring alkylation of both samarium atoms and arising from cleavage of the C-C bond connecting the two units, as well as complete reduction of the imine groups of the salophen ligands and THF deoxygenation. In the formula drawing depicted here the bridging phenylene rings are omitted for clarity.99 Carbene complexes of the lanthanide elements have first become available through the use of the stable Arduengo-type carbenes.100,101 Organolanthanide derivatives are readily accessible by adding the heterocyclic carbene ligands to various diand trivalent rare earth complexes such as decamethylsamarocene. Cyclopentadienyl-free derivatives have been obtained by reacting 1,3,4,5-tetramethylimidazol-2-ylidene with the tris(2,2,6,6-tetramethylheptane-3,5-dionato) complexes of yttrium and europium, Ln(THD)3 (Ln ) Y, Eu). The two carbene complexes 25 were isolated as white solids in quantitative yield. The europium complex was structurally characterized by X-ray analysis. Despite the differences in the ionic radii of the two metals 7-coordinate monocarbene adducts are formed in both cases. With 266.3(4) pm the Eu-C distance in (1,3,4,5-tetramethylimidazol-2-ylidene)Eu(THD)3 is comparable to Pr(III)-C and Sm(III)-C distances reported for some isonitrile complexes.102,103 In the 13C NMR spectrum of the yttrium complex the resonance for the former carbene carbon is at δ 199.38 (cf. δ 214 for the free carbene ligand) and shows a 13C-89Y coupling of 33 Hz which indicates that the Y-C bond does not dissociate rapidly on the NMR time scale.101 The bulkier 1,3-diisopropyl-4,5dimethylimidazol-2-ylidene (iPr-Carb) has been used to synthesize a mixed carbene-THF alkyl Lu(CH2SiMe3)3(THF)(Pr-Carb) (26).22d Due to its higher steric demand, the carbene ligand occupies an equatorial position (Lu-C(Carb) ) 249 pm). Somewhat related to the carbene complexes is a highly unusual monomeric samarium bis(iminophosphoranyl) chelate complex which has been reported by Cavell et al.104 Addition of H2C(Ph2PdNSiMe3)2 to a toluene solution of samarium tris(dicyclohexylamide) afforded bright yellow [κ-C,N,N′-C(Ph2Pd NSiMe3)2]Sm(NCy2)(THF) (27). The core of the molecule consists of two nearly planar, fused fourmembered rings with a Sm-C shared edge. With 246.7(4) pm the Sm-C bond length is considerably shorter (10%) than the average samarium-carbon distances, indicating that 27 can be formulated as a carbene complex. Non-Cyclopentadienyl Organolanthanide Complexes Chemical Reviews, 2002, Vol. 102, No. 6 1865

Synthesis and structural chemistry of non-cyclopentadienyl organolanthanide complexes.

Chemistry of the Carba-closo-dodecaborate(−) Anion, CB11H12-

Getting down to business: Reduction of the LaIII tricyclopentadienide complex [LaCp′′3] (Cp′′=η5-1,3-(SiMe3)2C5H3) by K and [18]crown-6 or [2,2,2]cryptand produced thermally stable mononuclear crystalline lanthanate(II) salts. The La +2 oxidation state in these complexes was confirmed both in solution (EPR) and the solid state (EPR, SQUID, X-ray diffraction) and was supported by a computational study.

Lanthanum does form stable molecular compounds in the +2 oxidation state.

The net reaction of monomeric Cp‘2CeH [Cp‘ = 1,3,4-(Me3C)3(C5H2)] in C6D6 with C6F6 is Cp‘2CeF, H2, and tetrafluorobenzyne. The pentafluorophenylmetallocene, Cp‘2Ce(C6F5), is formed as an intermediate that decomposes slowly to Cp‘2CeF and C6F4 (tetrafluorobenzyne), and the latter is trapped by the solvent C6D6 as a [2+4] cycloadduct. In C6F5H, the final products are also Cp‘2CeF and H2, which are formed from the intermediates Cp‘2Ce(C6F5) and Cp‘2Ce(2,3,5,6-C6F4H) and from an unidentified metallocene of cerium and the [2+4] cycloadducts of tetra- and trifluorobenzyne with C6D6. The hydride, fluoride, and pentafluorophenylmetallocenes are isolated and characterized by X-ray crystallography. DFT(B3PW91) calculations have been used to explore the pathways leading to the observed products of the exergonic reactions. A key step is a H/F exchange reaction which transforms C6F6 and the cerium hydride into C6F5H and Cp‘2CeF. This reaction starts by an η1-F−C6F5 interaction, which serves as a hook. The reaction pr...

Hydrogen for fluorine exchange in C6F6 and C6F5H by monomeric [1,3,4-(Me3C)3C5H2]2CeH: experimental and computational studies.

Cationic alkyl complexes of the rare-earth metals [LnRm(L)n](3–m)+ (R=alkyl; m=1, 2; L=Lewis base) were virtually unknown species until recently. Because of their increased Lewis acidity/electrophilicity they should have considerable potential as homogeneous catalysts in olefin polymerization and in organic transformations. They can be generated by treating the neutral rare-earth metal precursors containing at least two alkyl groups R with suitable Lewis or Bronsted acids in the presence of weakly coordinating anions. Not only monocationic but also dicationic alkyl derivatives have been shown to be accessible. In the context of modeling homogeneous ethylene polymerization using a mixture consisting of LnR3/AlR3/[NMe2HPh][B(C6F5)4], such dications were discovered. Some thermally robust examples of mono- and dicationic alkyl complexes have been structurally characterized as solvent-separated ion pairs. Neutral and monoanionic macrocycles such as crown ethers or aza-crown ethers as well as amidinato, β-diketiminato, and substituted cyclopentadienyl ligands are suitable ancillary ligands to stabilize the cationic alkyl fragments.

Cationic alkyl complexes of the rare-earth metals: Synthesis, structure, and reactivity

Synthesis and Structural Characterization of closo- and exo-nido-Lanthanacarboranes

exo-nido- versus closo-Lanthanacarboranes. Synthesis and Structure of exo-nido-[(C6H5CH2)2C2B10H10]Ln(DME)3, [exo-nido-{(C6H5CH2)2C2B9H9}Ln(THF)3]2 (Ln = Sm, Yb), and closo-exo-[(C6H5CH2)2C2B10H10]4Sm2Na3

Systematic studies on the reactions of lanthanide trichlorides with Na[1,3-bis(trimethylsilyl) cyclopentadienyl]. Crystal structures of [1,3-(Me3Si)2C5H3]3Ln (LnLa, Nd, Gd, Dy)

Treatment of unsolvated Cp″2Ln(II) [Cp″ = 1,3-(Me3Si)2C5H3] with 1 equivalent of Ag(I)Y, or reaction of [Cp″2LnI]2 with 2 molar equivalents of Ag(CB11Br6H6) in pure toluene at room temperature gave “Lewis base-free” cationic lanthanide metallocene complexes [Cp″2Ln]Y (Y = BPh4–, Ln = Sm 1, Yb 2; Y = CB11Br6H6–, Ln = Sm 3, Er 4) in good yield. They slowly undergo decomposition reaction at room temperature. The reactivity of these “Lewis base-free” cationic complexes is highly dependent upon the coordinating nature of the counter ions. Complexes 3 and 4 are much more reactive than 1 and 2. Recrystallization of 1 and 2 from 1,2-dimethoxyethane (DME) and THF yielded [Cp″2Sm(DME)][BPh4] 5 and [Cp″2Yb(THF)2][BPh4] 6, respectively. However, recrystallization of 3 and 4 from THF resulted in the ring-opening polymerization of THF. The THF coordinated complexes [Cp″2Ln(THF)2][CB11Br6H6] (Ln = Sm 7, Er 8) were isolated via recrystallization of 3 and 4 from toluene containing a small amount of THF. The “Lewis base-free” cation “Cp″2Er+” can abstract one bromine atom from the counter ion CB11Br6H6– or one chlorine atom from CH2Cl2 to form [Cp″2ErBr]2 or [Cp″2ErCl]2, respectively. Unfortunately, these cations do not exhibit reactivity towards 1-hexene at room temperature. Molecular structures of 5, 7, 8 and [Cp″2ErBr]2 have been confirmed by single-crystal X-ray analyses.

Zhixian Liu

Papers

Synthesis and Structural Characterization of closo- and exo-nido-Lanthanacarboranes

exo-nido- versus closo-Lanthanacarboranes. Synthesis and Structure of exo-nido-[(C6H5CH2)2C2B10H10]Ln(DME)3, [exo-nido-{(C6H5CH2)2C2B9H9}Ln(THF)3]2 (Ln = Sm, Yb), and closo-exo-[(C6H5CH2)2C2B10H10]4Sm2Na3

Systematic studies on the reactions of lanthanide trichlorides with Na[1,3-bis(trimethylsilyl) cyclopentadienyl]. Crystal structures of [1,3-(Me3Si)2C5H3]3Ln (LnLa, Nd, Gd, Dy)

Synthesis and reactivity of cationic lanthanide metallocene complexes. Hexabromocarborane and tetraphenylborate as counter ions

Synthesis and X-ray crystal structure of bis[η5-1,3-bis(trimethylsilyl)cyclopentadienyl] lanthanide and yttrium iodide complexes