Search results for "ALK"
showing 10 items of 4314 documents
An approach to erythrophleum alkaloids. Synthesis of methyl (−)-4-epi-cassamate
1986
Abstract A synthetic approach to Erythrophleum alkaloids, involving as a key-step the regiospecific deprotonation of the ketone 5a, is described.
Synthesis of Functionalized Indoles with an α-Stereogenic Ketone Moiety Through an Enantioselective Friedel-Crafts Alkylation with (E)-1,4-Diaryl-2-b…
2009
Chiral complexes of BINOL-based ligands with hafnium tert-butoxide catalyze the enantioselective Friedel-Crafts alkylation of indoles with (E)-1,4-diaryl-2-butene-1,4-diones at room temperature, with good yields and ee up to 94%. Hafnium(IV) was found to be a more effective Lewis acid than other frequently used metal ions such as titanium(IV) or zirconium(IV). Unlike the enantioselective Friedel-Crafts alkylation of indoles with α,β-unsaturated compounds where the stereogenic center is generated in the β-position to a carbonyl group, the Friedel-Crafts alkylation with 2-butene-1,4-diones described here generates an α-stereogenic center with respect to one of the carbonyl groups. This can be…
The first structurally characterized cationic lanthanide–alkyl complexesElectronic supplementary information (ESI) available: experimental and spectr…
2002
Reaction of rare earth metal–alkyl complexes [Ln(CH2SiMe3)3(THF)2] (Ln = Y, Lu) with B(C6X5)3 (X = H, F) in the presence of crown ethers gives crystallographically characterized ion pairs [Ln(CH2SiMe3)2(CE)(THF)n]+[B(CH2SiMe3)(C6X5)3]– (CE = [12]-crown-4, n = 1; CE = [15]-crown-5 and [18]-crown-6, n = 0).
Rare Earth Half-Sandwich Catalysts for the Homo- and Copolymerization of Ethylene and Styrene
2001
The synthesis of rare earth metal half-sandwich hydrido complexes [Ln(η5:η1-C5Me4SiMe2NCMe3)(THF)(μ-H)]2(Ln = Y, Lu, Yb, Er, Tb) through σ-bond metathesis of the alkyl complexes [Ln(η5:η1- C5Me4SiMe2NCMe3)(CH2SiMe3)(THF)], easily accessible by the reaction of the amino-cyclopentadiene with [Ln(CH2SiMe3)3(THF)2], was developed. The dimeric lanthanide hydrido complexes are highly fluxional involving THF dissociation and cis-trans isomerization of the linked amidocyclopentadienyl ligand. The presence of a monomer-dimer equilibrium is suggested by cross-over experiments. They were tested as single-site, single-component catalysts for the polymerization of ethylene, α-olefin, and styrene, as wel…
Boosting Vis/NIR Charge-Transfer Absorptions of Iron(II) Complexes by N-Alkylation and N-Deprotonation in the Ligand Backbone.
2017
Reversing the 3MLCT / 3MC excited state order in iron(II) complexes is a challenging objective, yet would finally result in longsought luminescent transition metal complexes with an earthabundant central ion. One approach to achieve this goal is based on low-energy charge transfer absorptions in combination with a strong ligand field. Coordinating electron rich and electron poor tridentate oligopyridine ligands with large bite angles at iron(II) enables both low-energy MLCT absorption bands around 590 nm and a strong ligand field. Variations of the electron rich ligand by introducing longer alkyl substituents destabilizes the iron(II) complex towards ligand substitution reactions while hard…
Titanium imido complexes stabilised by bis(iminophosphoranyl)methanide ligands: the influence of N-substituents on solution dynamics and reactivity
2014
Terminal titanium imido complexes of the general formula [Ti(N(t)Bu)Cl{CH(Ph2PNR)2}] 4 (R = Ph, (i)Pr, (t)Bu) are reported. These compounds were synthesized from the corresponding Li adducts 3 of BIPMH (bis(iminophosphoranyl)methanide) and Mountford's complex [Ti(N(t)Bu)Cl2(Py)3]. The crystal structures of two of the Ti complexes (R = Ph, (t)Bu) and two of the Li compounds (R = (i)Pr, (t)Bu) are reported. Dynamic solution NMR spectroscopy reveals a dynamic isomerisation process in the case of the Ti complex 4c (R = (t)Bu). DFT studies showed that this dynamic process comes from steric repulsion between the imido ligand and the (t)Bu N-substituents on the BIPMH ligand. Complexes 4 were teste…
N-Butylpyrrolidone (NBP) as a non-toxic substitute for NMP in iron-catalyzed C(sp2)–C(sp3) cross-coupling of aryl chlorides
2021
Although iron catalyzed cross-coupling reactions show extraordinary promise in reducing the environmental impact of more toxic and scarce transition metals, one of the main challenges is the use of reprotoxic NMP (NMP = N-methylpyrrolidone) as the key ligand to iron in the most successful protocols in this reactivity platform. Herein, we report that non-toxic and sustainable N-butylpyrrolidone (NBP) serves as a highly effective substitute for NMP in iron-catalyzed C(sp2)–C(sp3) cross-coupling of aryl chlorides with alkyl Grignard reagents. This challenging alkylation proceeds with organometallics bearing β-hydrogens with efficiency superseding or matching that of NMP with ample scope and br…
ChemInform Abstract: Catalytic Enantioselective Addition of Terminal Alkynes to Aromatic Aldehydes Using Zinc-Hydroxyamide Complexes.
2010
A mandelamide ligand, derived from (S)-mandelic acid and (S)-phenylethanamine, catalyzes the addition of aryl-, alkyl- and silyl-alkynylzinc reagents to aromatic and heteroaromatic aldehydes with good yields and good to high enantioselectivities.
Corroles with Group 15 Ions. 2. Synthesis and Characterization of Octaethylcorroles Containing a Phosphorus Central Atom
2001
The synthesis, spectroscopic characterization, and electrochemistry of five new phosphorus corroles are reported. The investigated complexes contain alkyl, aryl, oxo, or hydrido axial ligands and are represented as (OEC)P(H)2, (OEC)P(CH3)2, (OEC)P(C6H5)2, (OEC)P=O, and [(OEC)P(CH3)]+ClO4-, where OEC is the trianion of octaethylcorrole. The products of electrooxidation and/or electroreduction were also characterized by UV-vis and ESR spectroscopy. Correlations are shown to exist between reversible half-wave potentials for the first oxidation and first reduction of each compound and the combined electronegativity of the central ion and the axial ligand(s). The electrochemical HOMO-LUMO gap, d…
Catalytic enantioselective addition of terminal alkynes to aromatic aldehydes using zinc-hydroxyamide complexes
2009
[EN] A mandelamide ligand, derived from (S)-mandelic acid and (S)-phenylethanamine, catalyzes the addition of aryl-, alkyl-and silyl-alkynylzinc reagents to aromatic and heteroaromatic aldehydes with good yields and good to high enantioselectivities.