Selective Actinide-Catalyzed Tandem Proton-Transfer Esterification of Aldehydes with Alcohols for the Production of Asymmetric Esters

Actinide-catalyzed tandem proton-transfer esterification between aldehydes and alcohols is presented herein for the first time. It represents a novel convenient and external-oxidant-free methodology in the preparation of asymmetric ester compounds. Various kinds of aldehydes and alcohols can be applied to this reaction, affording the corresponding ester product in moderate to high yields. A plausible mechanism was proposed on the basis of the kinetic, stoichiometric, and deuterium-labeling studies

Tailor-Made Thermoplastic Elastomeric Stereoblock Polypropylenes by Modulation of Monomer Pressure

Tailor-Made Thermoplastic Elastomeric Stereoblock Polypropylenes by Modulation of Monomer Pressur

Catalytic 1,2-Regioselective Dearomatization of N‑Heteroaromatics via a Hydroboration

The thorium methyl and hydride complex (C₅Me₅)₂ThMe₂ and [(C₅Me₅)₂Th­(H)­(μ-H)]₂ catalyzed highly 1,2-regioselective dearomatization of pyridines via a hydroboration process is reported herein. Twelve different kinds of meta- and para-substituted pyridines are applicable to this reaction, giving the corresponding <i>N</i>-boryl-1,2-dihydropyridine products in high yields. Other N-heteroaromatic compounds, such as benzo-fused N-heterocycles, pyrazines, pyrimidines, 1,3,5-triazine, and benzothiazole, were also found to be hydroborated with high chemoselectivity. Kinetics including isotope effect studies revealed a first-order dependence on the concentration of catalyst, pyridine, and pinacolborane, with release of the dearomatized final product as the rate-determining step. A plausible mechanism is proposed on the basis of stoichiometric reactions and kinetic studies

Actinide Complexes Possessing Six-Membered N‑Heterocyclic Iminato Moieties: Synthesis and Reactivity

A novel class of ligand systems possessing a six-membered N-heterocyclic iminato [perimidin-2-iminato (Pr^RN, where R = isopropyl, cycloheptyl)] moiety is introduced. The complexation of these ligands with early actinides (An = Th and U) results in powerful catalysts [(Pr^RN)­An­(N­{SiMe₃)₂}₃] (<b>3</b>–<b>6</b>) for exigent insertion of alcohols into carbodiimides to produce the corresponding isoureas in short reaction times with excellent yields. Experimental, thermodynamic, and kinetic data as well as the results of stoichiometric reactions provide cumulative evidence that supports a plausible mechanism for the reaction

Synthesis of Coordinatively Unsaturated Tetravalent Actinide Complexes with η⁵ Coordination of Pyrrole

The synthesis of new actinide complexes utilizing bridged α-alkyl-pyrrolyl ligands is presented. Lithiation of the ligands followed by treatment with 1 equiv of actinide tetrachloride (uranium or thorium) produces the desired complex in good yield. X-ray diffraction studies reveal unique η⁵:η⁵ coordination of the pyrrolyl moieties; when the nonsterically demanding methylated ligand is used, rapid addition of the lithiated ligand solution to the metal precursor forms a bis-ligated complex that reveals η⁵:η¹ coordination as determined by crystallographic analysis

Actinide Amidinate Complexes with a Dimethylamine Side Arm: Synthesis, Structural Characterization, and Reactivity

The reactivity of monoanionic amidinate ligands containing a dimethylamine side arm with variable lengths of the linker chain and aromatic substituents of the ipso carbon atom was investigated for the early actinides thorium and uranium. The bis­(amidinate) actinide complexes obtained were structurally characterized, displaying a coordination of both dimethylamine nitrogen atoms to the respective metal center, allowing for a fine tuning of the reactivity of the complex by manipulation of the coordination environment around the metal center. The reactivity of the actinide amidinate complexes was studied in the catalytic ring-opening polymerization of ε-caprolactone

Elucidation of Substituent Effects in the Polymerization of Propylene Promoted by Titanium Amidinates

In polymerization reactions, the molecular weight of the polymer depends on the rates of monomer insertion, chain termination, and chain transfer. Here we do present studies indicating why chelating octahedral benzamidinate group IV complexes, which promote the polymerization of propylene with MAO, exhibit a linear free energy relationship with the <i>steric</i> Taft parameter. We correlate that this relationship is encountered with the para substituent of the aromatic ring, far away from the active catalytic site. A number of known events are put together to shed light on the effect of the ancillary ligands in the catalytic polymerization, and a new plausible mechanism for the process is presented

Addition of E–H (E = N, P, C, O, S) Bonds to Heterocumulenes Catalyzed by Benzimidazolin-2-iminato Actinide Complexes

The synthesis and characterization of benzimidazolin-2-iminato actinide­(IV) complexes [(Bim^R1/R2N)­An­(N­{SiMe₃}₂)₃] (An = U, Th) (<b>1</b>–<b>6</b>) is reported. All complexes were obtained in high yields, and their solid state structures were established through single-crystal X-ray diffraction analysis. Using <b>1</b>–<b>6</b> as precatalysts, the addition of mono- and bifunctional E–H (E = N, P, C, O, S) substrates to various heterocumulenes, including carbodiimides, isocyanates, and isothiocyanates, was investigated, affording the respective addition products in high yields under very mild reaction conditions. Various amines were applicable to this reaction, indicating a large scope capability of amine nucleophiles for the insertion process

Catalytic Addition of Alcohols to Carbodiimides Mediated by Benzimidazolin-2-iminato Actinide Complexes

The synthesis of methyl and methoxy substituted benzimidazolin-2-iminato actinide (IV) complexes (<b>1</b>–<b>4</b>), [(Bim^2‑MeOPh/MeN)­AnN″₃] and [(Bim_5‑Me^Dipp/MeN)­AnN″₃] (An = U, Th; N″ = N­(SiMe₃)₂), was performed by the protonolysis of the actinide metallacycles with the respective neutral benzimidazolin-2-imine ligand precursors. Full characterization, including X-ray diffraction studies for all the complexes, is reported. Despite the high oxophilicity of the actinide metal centers, these complexes displayed extremely high activities in the catalytic addition of aliphatic and aromatic alcohols to carbodiimides, under very mild conditions, providing a facile and highly efficient strategy for the construction of carbon–oxygen bonds. Various kinds of diols and triols can also be used in this intermolecular insertion, representing a large substrate scope for the application of these organoactinide precatalysts

Uranium(IV) Imidazolin-2-iminato Complexes: A New Class of Actinide Complexes

Acid–base reactions between imidazolin-2-imines (Im^RNH) and [U­(NMeEt)₄] selectively afforded uranium­(IV) imidazolin-2-iminato complexes of the type [U­(NIm^<i>t</i>Bu)₄] (<b>1</b>), [U­(NIm^Mes)₃(NMeEt)] (<b>2</b>), and [U­(NIm^Dipp)₂(NMeEt)₂] (<b>3</b>) depending on the steric demand of the substituents in the 1 and 3 positions of the imidazole heterocycle (R = <i>t</i>Bu, Mes, Dipp). This new class of actinide complexes displays short U–N bonds and nearly linear U–N–C bond angles, suggesting a U–N bond order higher than 1, as well as extraordinarily high catalytic activity in the polymerization of ε-caprolactone