Dinuclear Ce(IV) Aryloxides: Highly Active Catalysts for Anhydride/Epoxide Ring-Opening Copolymerization

Tripodal tris(siloxide) ligand supported trivalent rare-earth metal complexes and redox reactivity

Tripodal tris(siloxide) ligand supported rare-earth metal complexes LLn(III) (Ln = Ce, Pr, Tb, Y, Lu) were synthesized. The Ce(III) complex was oxidized with [N(C6H4Br)3][SbCl6] to a Ce(IV) chloride complex, which reacted with tBuONa to form a Ce(IV) tert-butoxide complex, one displaying a reduction potential cathodically shifted relative to that of Ce(IV) chloride complex.

Alkali metal carbonate catalyzed copolymerization of anhydrides and epoxides: a simple, efficient and versatile approach to well-defined alternating polyesters

Readily available and economical alkali metal carbonates have been utilized to catalyze the ROAC of PA and various epoxides to afford polyesters with perfectly alternating sequence distribution, controlled molar masses, and moderate dispersity.

Controlled monodefluorination and alkylation of C(sp3)-F bonds by lanthanide photocatalysts: importance of metal-ligand cooperativity

The controlled functionalization of a single fluorine in a CF3 group is difficult and rare. Photochemical C-F bond functionalization of the sp3-C-H bond in trifluorotoluene, PhCF3, is achieved using catalysts made from earth-abundant lanthanides, (CpMe4)2Ln(2-O-3,5- t Bu2-C6H2)(1-C{N(CH)2N(iPr)}) (Ln = La, Ce, Nd and Sm, CpMe4 = C5Me4H). The Ce complex is the most effective at mediating hydrodefluorination and defluoroalkylative coupling of PhCF3 with alkenes; addition of magnesium dialkyls enables catalytic C-F bond cleavage and C-C bond formation by all the complexes. Mechanistic experiments confirm the essential role of the Lewis acidic metal and support an inner-sphere mechanism of C-F activation. Computational studies agree that coordination of the C-F substrate is essential for C-F bond cleavage. The unexpected catalytic activity for all members is made possible by the light-absorbing ability of the redox non-innocent ligands. The results described herein underscore the importance of metal-ligand cooperativity, specifically the synergy between the metal and ligand in both light absorption and redox reactivity, in organometallic photocatalysis.

Perfectly Alternating Copolymerization of Cyclic Anhydrides and Epoxides with Yttrium β-Diketiminate Complexes

Monometallic yttrium β-diketiminate complexes are active and controlled catalysts for perfectly alternating ring-opening copolymerization of 1-butene oxide and phthalic anhydride under mild conditions. β-Diketiminate ligands with pendant neutral donors were targeted to identify both the impact of donor strength and number of donors on rates of polymerization and the presence of undesirable side reactions. Initiating groups were also varied between alkyls, chlorides, and alkoxides. In the presence of a cocatalyst, the catalysts studied were active for polymerization with minimal side reactions, whereas lack of cocatalysts led to competing homopolymerization of epoxides. While a greater donor strength and a larger number of donors both increase the rate of polymerization, donor strength generally had a bigger impact when a cocatalyst was used. Additionally, alkoxide and chloride initiators proved to be the fastest, with alkyls being more sluggish. These subtle ligand changes significantly impacting polymerization activity lend promise to the facile tunability of rare earth metal complexes to be highly active for the target copolymerization, which renders further research in this area attractive and timely.

A Combined Experimental and Theoretical Investigation of Arene-Supported Actinide and Ytterbium Tetraphenolate Complexes

Modular tetraphenolate ligands tethered with a protective arene platform (para-phenyl or para-terphenyl) are used to support mononuclear An(IV) (An = Th, U) complexes with an exceptionally large and open axial coordination site at the metal. The base-free complexes and a series of neutral donor adducts were synthesized and characterized by spectroscopies and single-crystal X-ray diffraction. Anionic Th(IV) -ate complexes with an additional axial aryloxide ligand were also synthesized and characterized. The para-phenyl-tethered mononuclear complexes exhibit rare An(IV)-arene interactions, and the An(IV)-arene distance broadly increases with axial donor strength. The para-terphenyl-tethered complexes have almost no interaction with the arene base, isolating the central metal cation. Computational analysis of the mononuclear complexes and their reduced analogues, and Yb(III) congeners, as well as the effect of additional donor ligand binding, seek to elucidate the electronic structure of the metal-arene interactions and establish whether they, or their reduced or oxidized counterparts, could function as molecular qubits.

Pentamethylcyclopentadienyl Complexes of Cerium(IV): Synthesis, Reactivity, and Electrochemistry

Treatment of Cp*₂CeCl₂K(THF) with alkali-metal alkoxides and siloxides in the presence of hexachloroethane generates the monomeric bis(pentamethylcyclopentadienyl) cerium(IV) complexes Cp*₂Ce(OR)₂ (Cp* = C₅Me₅; R = Et, iPr, CH₂tBu, tBu, SiMe₃, or SiPh₃). Large substituents R trigger ligand scrambling to half-sandwich complexes Cp*Ce(OR)₃, which could be isolated for R = tBu and SiPh₃. Similar reactions with sodium aryloxide NaOAr (OAr = OC₆H₃iPr₂-2,6) led to Cp*₂Ce(OAr)Cl. Treatment of tris(cyclopentadienyl) complexes Cp^R₃CeCl (Cp^H = Cp = C₅H₅; Cp^Me = C₅H₄Me) with NaOAr afforded Cp^Me₂Ce(OAr)₂ and Cp₃Ce(OAr). The cerium(IV) complexes display a pseudotetrahedral geometry in the solid state. Cyclic voltammetry revealed mostly chemically reversible as well as electrochemically quasi-reversible redox processes with potentials ranging from -0.84 to -1.61 V versus Fc/Fc⁺. Switching from sandwich to half-sandwich complexes decreased the electrochemical potentials drastically, showing better stabilization of the cerium(IV) center in the case of Cp*Ce(OR)₃ than in the case of Cp*₂Ce(OR)₂. Enhanced stabilization of the cerium +IV oxidation state could be further demonstrated in the series alkoxy > siloxy > aryloxy as well as C₅Me₅ > C₅HMe₄.