Cerium-Catalyzed Hydrosilylation of Acrylates to Give α-Silyl Esters

Structure and Magnetic Properties of Homoleptic Trivalent Tris(alkyl)lanthanides

Six new solvent-free, homoleptic paramagnetic tris(alkyl)lanthanides Ln{C(SiHMe₂)₃}₃ (1Ln) and Ln{C(SiHMe₂)₂Ph}₃ (2Ln) (Ln = Gd, Dy, and Er) were synthesized to investigate the magnetic properties of 4f organometallic compounds stabilized by secondary Ln↼H-Si and benzylic interactions. The unit cell of 1Gd contains one independent molecule (Z = 2), while 1Dy and 1Er crystallize with four independent isostructural molecules per unit cell (Z = 16). In all molecules, as in other 1Ln compounds, the three tris(dimethylsilyl)methyl ligands form a trigonal planar LnC₃ core, and six secondary interactions involving Ln↼H-Si bonding in Ln{C(SiHMe₂)₃}₃ form above and below the equatorial plane. Two and five crystallographically independent molecules of each 2Ln (2Gd, Z = 8; 2Dy, Z = 20) form with three π-coordinated phenyl groups in addition to either one or two secondary Ln↼H-Si interactions per molecule. The packing of these midseries organolanthanide compounds contrasts the single crystallographically unique molecules in previously reported La{C(SiHMe₂)₃}₃ (1La, Z = 2, Z' = 1) and La{C(SiHMe₂)₂Ph}₃ (2La, Z = 2, Z' = 1/3). 2La doped with 2Dy can adopt the crystallographic structure of 2La, which promotes magnetic properties, namely a higher χ_mT value at low temperatures as well as stronger magnetic anisotropy. The ac susceptibility data for 10% 2Dy doped into 2La suggests slow relaxation at low temperatures with a relaxation barrier of ∼45 K. The computed saturated magnetization of 1Er (M ≈ 4.5 μ_B) and 1Dy (M ≈ 6 μ_B) matches the experimental values, while the computed value for 2Dy better matches the value measured for 2Dy diluted in 2La (M ≈ 5 μ_B). Gas-phase calculations predict that the ground-state and first excited-state multiplet separations are larger for 1Er than 2Er, while the ordering for dysprosium is 1Dy > 2Dy.

Cerium-Oxo clusters for photocatalytic aerobic oxygenation of sulfides to sulfoxides

Two cerium-oxo clusters (COCs) 1 and 2 are constructed by self-assembly of cerium ions and carboxylate ligands. Both clusters feature spherical structures resembling the key moiety of fluorite phase CeO2,...

CeCl3 /n-BuLi: Unraveling Imamoto's Organocerium Reagent

CeCl₃(thf) reacts at low temperatures with MeLi, t‐BuLi, and n‐BuLi to isolable organocerium complexes. Solvent‐dependent extensive n‐BuLi dissociation is revealed by ⁷Li NMR spectroscopy, suggesting “Ce(n‐Bu)₃(thf)_x” or solvent‐separated ion pairs like “[Li(thf)₄][Ce(n‐Bu)₄(thf)_y]” as the dominant species of the Imamoto reagent. The stability of complexes Li₃Ln(n‐Bu)₆(thf)₄ increases markedly with decreasing Ln^III size. Closer inspection of the solution behavior of crystalline Li₃Lu(n‐Bu)₆(thf)₄ and mixtures of LuCl₃(thf)₂/n‐BuLi in THF indicates occurring n‐BuLi dissociation only at molar ratios of <1:3. n‐BuLi‐depleted complex LiLu(n‐Bu)₃Cl(tmeda)₂ was obtained by treatment of Li₂Lu(n‐Bu)₅(tmeda)₂ with ClSiMe₃, at the expense of LiCl incorporation. Imamoto's ketone/tertiary alcohol transformation was examined with 1,3‐diphenylpropan‐2‐one, affording 99 % of alcohol.

Emergence of a New [NNN] Pincer Ligand via Si-H Bond Activation and β-Hydride Abstraction at Tetravalent Cerium

The cerium(IV) pyrazolate complexes [Ce(Me2 pz)4 ]2 and [Ce(Me2 pz)4 (thf)] initiate β-hydride abstraction of the bis(dimethylsilyl)amido moiety, to afford a heteroleptic cerium(IV) species containing a dimethylpyrazolyl-substituted silylamido ligand, namely [Ce(Me2 pz)3 (bpsa)] (bpsa=bis((3,5-dimethylpyrazol-1-yl)dimethylsilyl)amido; Me2 pz =3,5-dimethylpyrazolato), along with some cerium(III) species. Remarkably, the nucleophilic attack of the pyrazolyl at the silicon atom and concomitant Si-H-bond cleavage is restricted to the tetravalent cerium oxidation state and appears to proceed via the formation of a transient cerium(IV) hydride, which engages in immediate redox chemistry. When [Ce(Me2 pz)4 ]2 is treated with [Li{N(SiMe3 )2 }], that is, in the absence of the SiH functionality, any redox chemistry did not occur. Instead, the ceric ate complex [LiCe2 (Me2 pz)9 ] and the stable mixed-ligand ceric species [Ce(Me2 pz)2 {N(SiMe3 )2 }2 ] were obtained.

Stereospecific Si-C coupling and remote control of axial chirality by enantioselective palladium-catalyzed hydrosilylation of maleimides

Hydrosilylation of unsaturated carbon-carbon bonds with hydrosilanes is a very important process to access organosilicon compounds and ranks as one of the most fundamental reactions in organic chemistry. However, catalytic asymmetric hydrosilylation of activated alkenes and internal alkenes has proven elusive, due to competing reduction of carbon-carbon double bond or isomerization processes. Herein, we report a highly enantioselective Si-C coupling by hydrosilylation of carbonyl-activated alkenes using a palladium catalyst with a chiral TADDOL-derived phosphoramidite ligand, which inhibits O-hydrosilylation/olefin reduction. The stereospecific Si-C coupling/hydrosilylation of maleimides affords a series of silyl succinimides with up to 99% yield, >99:1 diastereoselectivity and >99:1 enantioselectivity. The high degree of stereoselectivity exerts remote control of axial chirality, leading to functionalized, axially chiral succinimides which are versatile building blocks. The product utility is highlighted by the enantioselective construction of N-heterocycles bearing up to three stereocenters.

Catalytic asymmetric hydrosilylation of internal alkenes has proven elusive due to more favourable double bond reduction or isomerization. Here, the authors show an enantioselective Si-C coupling by hydrosilylation of activated alkenes using a palladium/phosphoramidite catalyst affording axially chiral succinimides.

Rare earth arylsilazido compounds with inequivalent secondary interactions

A new bulky silazido ligand, -N(SiHMe2)Dipp (Dipp = C6H3-2,6-iPr2), supports planar, three-coordinate homoleptic rare earth complexes Ln{N(SiHMe2)Dipp}3 (Ln = Sc, Y, and Lu), each containing three secondary Ln↼HSi interactions and one agostic CH bond. Y{N(SiHMe2)Dipp}3 and acetophenone react via hydrosilylation, rather than by insertion into the Y-N bond or by enolate formation.

Homoleptic Trivalent Tris(alkyl) Rare Earth Compounds

Homoleptic tris(alkyl) rare earth complexes Ln{C(SiHMe₂)₃}₃ (Ln = La, 1a; Ce, 1b; Pr, 1c; Nd, 1d) are synthesized in high yield from LnI₃THF_n and 3 equiv of KC(SiHMe₂)₃. X-ray diffraction studies reveal 1a-d are isostructural, pseudo-C₃-symmetric molecules that contain two secondary Ln↼HSi interactions per alkyl ligand (six total). Spectroscopic assignments are supported by comparison with Ln{C(SiDMe₂)₃}₃ and DFT calculations. The Ln↼HSi and terminal SiH exchange rapidly on the NMR time scale at room temperature, but the two motifs are resolved at low temperature. Variable-temperature NMR studies provide activation parameters for the exchange process in 1a (ΔH^⧧ = 8.2(4) kcal·mol^-1; ΔS^⧧ = -1(2) cal·mol^-1K^-1) and 1a-d₉ (ΔH^⧧ = 7.7(3) kcal·mol^-1; ΔS^⧧ = -4(2) cal·mol^-1K^-1). Comparisons of lineshapes, rate constants (k_H/k_D), and slopes of ln(k/T) vs 1/T plots for 1a and 1a-d₉ reveal that an inverse isotope effect dominates at low temperature. DFT calculations identify four low-energy intermediates containing five β-Si-H⇀Ln and one γ-C-H⇀Ln. The calculations also suggest the pathway for Ln↼HSi/SiH exchange involves rotation of a single C(SiHMe₂)₃ ligand that is coordinated to the Ln center through the Ln-C bond and one secondary interaction. These robust organometallic compounds persist in solution and in the solid state up to 80 °C, providing potential for their use in a range of synthetic applications. For example, reactions of Ln{C(SiHMe₂)₃}₃ and ancillary proligands, such as bis-1,1-(4,4-dimethyl-2-oxazolinyl)ethane (HMeC(Ox^Me2)₂) give {MeC(Ox^Me2)₂}Ln{C(SiHMe₂)₃}₂, and reactions with disilazanes provide solvent-free lanthanoid tris(disilazides).

Homoleptic organolanthanide compounds supported by the bis(dimethylsilyl)benzyl ligand

A β-SiH functionalized benzyl anion [C(SiHMe₂)₂Ph]⁻ reacts with early rare earth halides to provide homoleptic tris(alkyl)lanthanides containing secondary interactions in an efficient and high yielding route.

Graphene-enhanced platinum-catalysed hydrosilylation of amides and chalcones: a sustainable strategy allocated with in situ heterogenization and multitask application of H2PtCl6

This work developed a new sustainable strategy with comprehensive utilization of recovered catalyst, which the organosilicon/graphene-supported platinum catalyst prepared from reduction of amides could be further used in the 1,4-hydrosilylation of chalcones.