Organometallic compounds of the lanthanides

Ga+-catalyzed hydrosilylation? About the surprising system Ga+/HSiR3/olefin, proof of oxidation with subvalent Ga+ and silylium catalysis with perfluoroalkoxyaluminate anions

Already 1 mol% of subvalent [Ga(PhF)2]+[pf]- ([pf]- = [Al(ORF)4]-, RF = C(CF3)3) initiates the hydrosilylation of olefinic double bonds under mild conditions. Reactions with HSiMe3 and HSiEt3 as substrates efficiently yield anti-Markovnikov and anti-addition products, while bulkier substrates such as HSiiPr3 are less reactive. Investigating the underlying mechanism by gas chromatography and STEM analysis, we unexpectedly found that H2 and metallic Ga0 formed. Without the addition of olefins, the formation of R3Si-F-Al(ORF)3 (R = alkyl), a typical degradation product of the [pf]- anion in the presence of a small silylium ion, was observed. Electrochemical analysis revealed a surprisingly high oxidation potential of univalent [Ga(PhF)2]+[pf]- in weakly coordinating, but polar ortho-difluorobenzene of E 1/2(Ga+/Ga0; oDFB) = +0.26-0.37 V vs. Fc+/Fc (depending on the scan rate). Apparently, subvalent Ga+, mainly known as a reductant, initially oxidizes the silane and generates a highly electrophilic, silane-supported, silylium ion representing the actual catalyst. Consequently, the [Ga(PhF)2]+[pf]-/HSiEt3 system also hydrodefluorinates C(sp3)-F bonds in 1-fluoroadamantane, 1-fluorobutane and PhCF3 at room temperature. In addition, both catalytic reactions may be initiated using only 0.2 mol% of [Ph3C]+[pf]- as a silylium ion-generating initiator. These results indicate that silylium ion catalysis is possible with the straightforward accessible weakly coordinating [pf]- anion. Apparently, the kinetics of hydrosilylation and hydrodefluorination are faster than that of anion degradation under ambient conditions. These findings open up new windows for main group catalysis.

Reactivity of Mixed Methyl-Aminobenzyl Guanidinate Lutetium Complex towards iPrN=C=NiPr, CS2 and Ph2PH

A heteroleptic terminal alkyl lutetium complex stabilized by a bulky guanidinato ligand, LLu(CH2C6H4NMe2-o)(Me)(THF) (1) (L = (PhCH2)2NC(NC6H3iPr2-2,6)2) has been synthesized by treatment of LLu(CH2C6H4NMe2-o)2 with AlMe3 (1 equiv) via an...

Synthesis and Reduction of Bimetallic Methyl-Bridged Rare-Earth Metal Complexes, [(C5H4SiMe3)2Ln(μ-CH3)]2 (Ln = Y, Tb, Dy)

The complexes [Cp'₂Ln(μ-CH₃)]₂, (Cp' = C₅H₄SiMe₃; Ln = Y, Tb, Dy) were reduced to determine if these methyl-bridged complexes would form mixed valent 4f ⁿ 5d¹ Ln(II)/4f ⁿ Ln(III) compounds or bimetallic 4f ⁿ 5d¹ Ln(II) compounds containing 5d¹-5d¹ metal-metal bonds upon reduction. Reaction of the known bridged-chloride complexes, [Cp'₂Ln(μ-Cl)]₂, 1-Ln (Ln = Y, Tb, Dy), with MeLi forms the bridged-methyl complexes [Cp'₂Ln(μ-CH₃)]₂, 2-Ln, which were crystallographically characterized for Tb and Dy. KC₈ reduction of 2-Ln in the presence of 2.2.2-cryptand produced 3-Y, 3-Tb, and 3-Dy, which exhibited intense dark colors and broad absorbance peaks around 400 nm with molar extinction coefficients of 1700, 2300, and 1800 M^-1 cm^-1, respectively, which are characteristics of Ln(II) ions. The dark maroon 3-Y product had an axial electron paramagnetic resonance spectrum at 77 K (g ₁ = 1.99, A ₁ = 17.9 G; g ₂ = 2.00, A ₂ = 17.7 G) and a two-line isotropic spectrum at 273 K (g = 1.99, A = 18.4 G), which indicates that an Y(II) ion is present. Although these results are indicative of Ln(II) ions present in the solution, crystallographic evidence was not obtained to establish the structure of these complexes.

Hydrosilylation reaction of olefins: recent advances and perspectives

This review focuses on the recent development of efficient, selective, and cheaper hydrosilylation catalyst systems appearing in the last decade.

Differences in the cyclometalation reactivity of bisphosphinimine-supported organo-rare earth complexes

A novel yttrium complex [L_nY(CH₂SiMe₃)₂] is resistant to cyclometalation, while samarium variants undergo C–H activation, forming unique cyclometalated motifs.

Recent advances in organothorium and organouranium catalysis

In this critical review we summarize the latest results obtained during the last decade concerning the catalytic activities of organoactinide complexes. We begin with a brief summary of the synthesis and characterization of uranium and thorium complexes that later will be used as catalysts for demanding chemical transformations. Hydroamination, hydrosilylation of terminal alkynes, coupling of terminal alkynes with isonitriles, catalytic reduction of azides and hydrazines, ring opening polymerization of cyclic esters and polymerization of alpha-olefins are covered in this review (118 references). The topics covered in this review regarding organoactinide chemistry will be of interest to inorganic, organic and organometallic chemists, material and catalytic scientists due to its unique mode of activation as compared to late transition-metals. In addition, the field of organoactinide complexes in catalysis is steadily growing, because of the complementary reactivity of organoactinides as compared to other early or late transition complexes, in demanding chemical transformations.

Analysis of Uranium Azide and Nitride Complexes by Atmospheric Pressure Chemical Ionization Mass Spectrometry

Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) has been used to characterize the air-sensitive paramagnetic organouranium azide and nitride complexes [(C5Me5)2UN3(mu-N3)]3 and [(C5Me5)U(mu-I)2]3N, respectively. The trimetallic complex [(C5Me5)U(mu-I)2]3E had been identified by X-ray crystallography, but the data did not definitively identify E as N3- versus O2- or (OH)-, a common problem in heavy-element nitride complexes involving metals with variable oxidation states. A comparison of the 250 degrees C APCI-MS spectra of products made from NaN3 and Na15NNN showed mixed [M]+ and [M + H]+ envelopes at expected ion intensities for the 14N and 15N isotopomers. A compilation of U-C(C5Me5) and U-I bond distance data for U3+ and U4+ is also reported that shows that the ranges for the two oxidation states have significant overlap.

Multiple C−H Bond Activation in Group 3 Chemistry: Synthesis and Structural Characterization of an Yttrium−Aluminum−Methine Cluster

Complete donor-induced alkylaluminate cleavage of halfmetallocene complex Cp*Y(AlMe4)2, that is, treatment of Cp*Y(AlMe4)2 with 2 equiv of diethyl ether, produces [Cp*Y(mu2-Me)2]3 in high yield (95%). In contrast, the equimolar reaction of Cp*Y(AlMe4)2 with diethyl ether reproducibly formed complex [Cp*4Y4(mu2-CH3)2{(CH3)Al(mu2-CH3)2}4(mu4-CH)2] in low yield (10-30%) via a multiple C-H bond activation. The synthesis of the heterooctametallic yttrium-aluminum-methine cluster was also accomplished in moderate yield (47%) by the equimolar reaction of discrete Cp*Y(AlMe4)2 and [Cp*Y(mu2-Me)2]3 in the absence of any donor solvent and "free" AlMe3. This gives strong evidence that preformed heterometal-bridged Y-CH3-Al moieties are prone to multiple hydrogen abstraction in the presence of a highly basic reagent such as [Cp*Y(mu2-Me)2]3. The monocylopentadienyl complexes [Cp*Y(mu2-Me)2]3 and [Cp*4Y4(mu2-CH3)2{(CH3)Al(mu2-CH3)2}4(mu4-CH)2] were structurally characterized.

Alkyl, Silyl, and Phosphane Ligands-Classical Ligands in Nonclassical Bonding Modes

Alkyl, silyl, and phosphane ligands are amongst the most familiar and ubiquitous ligands in organometallic and coordination chemistry. The C, Si, and P donor atoms of these ligands are sp(3)-hybridized and the ligands are related to each other by the isolobal analogy: (CR(3))(-)⥈(SiR(3))(-)⥈PR(3). Herein, we demonstrate that although a number of unusual observations concerning the reactivity and bonding of these ligands appears unrelated at first sight, they in fact provide offer an exiting and consistent picture that may form the basis for new paradigms. The characterization of stable complexes in which alkyl, silyl, and phosphane ligands behave as symmetrical bridges confirms that there is no inherent thermodynamic instability associated with these bonding situations, and, in fact, reactivity studies suggest that these ligands should be able to bridge between metal centers in reaction intermediates or transition states.

A diastereoselective intramolecular hydroamination approach to the syntheses of (+)-, (+/-)-, and (-)-pinidinol

A diastereoselective, lanthanocene-catalyzed, intramolecular hydroamination reaction was applied to the preparation of 2,6-disubstituted piperidines. Various metal/ligand arrays in the catalysts were examined using a model substrate to allow optimization of the diastereoselectivity. It was determined that the relationship between metal size and ligand bulk plays an integral role in the transformation. The complex Cp2NdCH(TMS)2 converted 2-substituted 8-nonen-4-amines to 2,6-disubsituted piperidines with greater than 100:1 selectivity for the formation of the cis isomer. A short synthesis of pinidinol, an alkaloid isolated from various pine and spruce species, was then carried out to exploit this stereoselective reaction.

Organoyttrium-catalyzed sequential Cyclization/Silylation reactions of nitrogen-heteroaromatic dienes demonstrating "Aryl-Directed" regioselectivity

The reaction of 1-allyl-2-vinyl-1H-pyrroles and 1-allyl-2-vinyl-1H-indoles with arylsilanes in the presence of catalytic [Cp(TMS)(2)Y(&mgr;-Me)](2) leads to highly selective cyclization/silylation events. In this process the active catalyst for the reaction, "Cp(TMS)(2)YH", undergoes initial olefin insertion at the vinyl group. Even isopropenyl substituents on the heteroaromatics react in preference to less sterically encumbered allyl groups. Furthermore, the observed regioselectivity reflects an "aryl-directed" process, whereby the more highly substituted secondary or tertiary organometallic is initially generated. This intermediate undergoes cyclization onto the remaining alkene and subsequent silylation by a sigma-bond metathesis reaction, affording the observed products.