Radical anionic versus neutral 2,2′-bipyridyl coordination in uranium complexes supported by amide and ketimide ligands

The synthesis and characterization of (bipy)₂U(N[t-Bu]Ar)₂ (1-(bipy)₂, bipy = 2,2′-bipyridyl, Ar = 3,5-C₆H₃Me₂), (bipy)U(N[1Ad]Ar)₃ (2-bipy), (bipy)₂U(NC[t-Bu]Mes)₃ (3-(bipy)2, Mes = 2,4,6-C₆H₂Me₃), and IU(bipy)(NC[t-Bu]Mes)₃ (3-I-bipy) are reported. X-ray crystallography studies indicate that bipy coordinates as a radical anion in 1-(bipy)₂ and 2-bipy, and as a neutral ligand in 3-I-bipy. In 3-(bipy)₂, one of the bipy ligands is best viewed as a radical anion, the other as a neutral ligand. The electronic structure assignments are supported by NMR spectroscopy studies of exchange experiments with 4,4′-dimethyl-2,2′-bipyridyl and also by optical spectroscopy. In all complexes, uranium was assigned a +4 formal oxidation state.National Science Foundation (U.S.) (Grant CHE-9988806

Preparation of multiblock copolymers via step-wise addition of l-lactide and trimethylene carbonate.

Poly(l-lactide) (PLA) is a bioderived and biodegradable polymer that has limited applications due to its hard and brittle nature. Incorporation of 1,3-trimethylene carbonate into PLA, in a block copolymer fashion, improves the mechanical properties, while retaining the biodegradability of the polymer, and broadens its range of applications. However, the preparation of 1,3-trimethylene carbonate (TMC)/l-lactide (LA) copolymers beyond diblock and triblock structures has not been reported, with explanations focusing mostly on thermodynamic reasons that impede the copolymerization of TMC after lactide. We discuss the preparation of multiblock copolymers via the ring opening polymerization (ROP) of LA and TMC, in a step-wise addition, by a ferrocene-chelating heteroscorpionate zinc complex, {[fc(PPh2)(BH[(3,5-Me)2pz]2)]Zn(μ-OCH2Ph)}2 ([(fcP,B)Zn(μ-OCH2Ph)]2, fc = 1,1'-ferrocenediyl, pz = pyrazole). The synthesis of up to pentablock copolymers, from various combinations of LA and TMC, was accomplished and the physical, thermal, and mechanical properties of the resulting copolymers evaluated

An Unusual Hydrogen Migration/C−H Activation Reaction with Group 3 Metals

A novel hydrogen migration from the phenyl ring to the pyridine ring of an yttrium pyridyl complex supported by a 1,1′-ferrocene diamide ligand is reported. Density functional theory calculations were instrumental in probing the mechanism for this transformation

Reaction of Group III Biheterocyclic Complexes

Group III alkyl complexes supported by a ferrocene diamide ligand (1,1′-fc(NSitBuMe_2)_2) have been found to be reactive toward aromatic N-heterocycles such as 1-methylimidazole and pyridines. These reactions were investigated experimentally and computationally. An initial C−H activation event is followed by a coupling reaction to form biheterocyclic complexes, in which one of the rings is dearomatized. In the case of 1-methylimidazole, the biheterocyclic compound could not be isolated and further led to an imidazole ring-opened product; in the case of pyridines, it transformed into an isomer with extended conjugation of double bonds. Mechanisms for both reactions are proposed on the basis of experimental and computational results. DFT calculations were also used to show that an energetically accessible pathway for the ring-opening of pyridines exists

Zirconium complexes supported by a ferrocene-based ligand as redox switches for hydroamination reactions

The synthesis of (thiolfan*)Zr(Net_2)_2 (thiolfan* = 1,1′-bis(2,4-di-tert-butyl-6-thiophenoxy)ferrocene) and its catalytic activity for intramolecular hydroamination are reported. In situ oxidation and reduction of the metal complex results in reactivity towards different substrates. The reduced form of (thiolfan*)Zr(Net_2)_2 catalyzes hydroamination reactions of primary aminoalkenes, whereas the oxidized form catalyzes hydroamination reactions of secondary aminoalkenes

Methine (CH) Transfer via a Chlorine Atom Abstraction/Benzene-Elimination Strategy: Molybdenum Methylidyne Synthesis and Elaboration to a Phosphaisocyanide Complex

Methine (CH) transfer to an open coordination site was achieved in one pot by titanium(III) abstraction of Cl from 7-chloronorbornadiene, radical capture by Mo, and benzene extrusion. This efficient Mo methylidyne synthesis permitted elaboration to an anionic phosphaisocyanide derivative upon deprotonation, functionalization with dichlorophenylphosphine, and ultimate reduction

Radical Scission of Symmetrical 1,4-Dicarbonyl Compounds: C−C Bond Cleavage with Titanium(IV) Enolate Formation and Related Reactions

Reaction of Ti(NRAr^1)_3 (1, R = C(CH_3)_3, Ar^1 = 3,5-C_6H_3Me_2) with 0.5 equiv of symmetrical 1,4-diketones (ArCOCH_2)_2 (Ar = p-Tol or p-MeOC_6H_4) in hydrocarbon solvents at ≤25 °C resulted in carbon−carbon bond cleavage with clean formation of titanium-bound enolates, 1-OC(CH_2)Ar. Treatment of Ti(NRAr^1)_3 with esters or amides of succinic acid, under the same mild conditions, smoothly produced titanium(IV) compounds containing the corresponding amide or ester enolate moiety. The amide enolate condenses with benzaldehyde in an aldolic fashion. Differences in the observed reactivity of amido-enolate vs ketone-derived enolate toward aldol condensation were interpreted with the help of computational methods. Upon reaction with Ti(NRAr^1)_3, para-substituted acetophenones yielded equal amounts of enolate and alkoxide products. Under similar experimental conditions, acetophenone itself produced quantitatively a species whose proposed structure incorporates characteristics reminiscent of a Gomberg dimer. This intermediate decomposes cleanly to the expected enolate and alkoxide mixture upon heating. Ti(NRAr^1)_3 reductively complexes substrates such as N-methyl phthalimide. Treatment of Ti(NRAr^1)_3 with 0.5 equiv of o-bromophenyl allyl ether resulted in bromine atom abstraction followed by cyclization of the intermediate aryl radical to generate a titanium-bound 3-methylenedihydrobenzofuran product

Zirconium complexes supported by a ferrocene-based ligand as redox switches for hydroamination reactions

The synthesis of (thiolfan*)Zr(Net_2)_2 (thiolfan* = 1,1′-bis(2,4-di-tert-butyl-6-thiophenoxy)ferrocene) and its catalytic activity for intramolecular hydroamination are reported. In situ oxidation and reduction of the metal complex results in reactivity towards different substrates. The reduced form of (thiolfan*)Zr(Net_2)_2 catalyzes hydroamination reactions of primary aminoalkenes, whereas the oxidized form catalyzes hydroamination reactions of secondary aminoalkenes