Luminescent Ce(III) complexes, Ce[N(SiMe3)2]3 (1) and [(Me3Si)2NC(RN)2]Ce[N(SiMe3)2]2 (R = (i)Pr, 1-(i)Pr; R = Cy, 1-Cy), with C(3v) and C(2v) solution symmetries display absorptive 4f → 5d electronic transitions in the visible region. Emission bands are observed at 553, 518, and 523 nm for 1, 1-(i)Pr, and 1-Cy with lifetimes of 24, 67, and 61 ns, respectively. Time-dependent density functional theory (TD-DFT) studies on 1 and 1-(i)Pr revealed the (2)A1 excited states corresponded to singly occupied 5d(z(2)) orbitals. The strongly reducing metalloradical character of 1, 1-(i)Pr, and 1-Cy in their (2)A1 excited states afforded photochemical halogen atom abstraction reactions from sp(3) and sp(2) C-X (X = Cl, Br, I) bonds for the first time with a lanthanide cation. The dehalogenation reactions could be turned over with catalytic amounts of photosensitizers by coupling salt metathesis and reduction to the photopromoted atom abstraction reactions.

Carbon-carbon bonds, including those between sp 3 -hybridized carbons (alkyl-alkyl bonds), typically comprise much of the framework of organic molecules. In the case of sp 3 -hybridized carbons, the carbon can be stereogenic, and the particular stereochemistry can have implications for structure and/or function 1 , 2 , 3 . As a consequence, the development of methods that simultaneously construct alkyl-alkyl bonds and control stereochemistry is a highly important, as well as a challenging, objective. Herein, a new strategy for enantioselective alkyl-alkyl bond formation is described, wherein a racemic alkyl electrophile is coupled with an olefin in the presence of a hydrosilane, through the action of a chiral nickel catalyst. Families of racemic alkyl halides, including tertiary substrates, that have not previously proved to be suitable for enantioconvergent couplings with alkylmetal nucleophiles are shown to cross-couple with olefins with good enantioselectivity and yield under very mild conditions. Given the ready availability of olefins, this new approach opens the door to the development of ever more general and powerful methods for enantioconvergent alkyl-alkyl coupling.

Two complete mixed-ligand series of luminescent Ce(III) complexes with the general formulas [(Me3Si)2NC(N(i)Pr)2]xCe(III)[N(SiMe3)2]3-x (x = 0, 1-N; x = 1, 2-N, x = 2, 3-N; x = 3, 4) and [(Me3Si)2NC(N(i)Pr)2]xCe(III)(OAr)3-x (x = 0, 1-OAr; x = 1, 2-OAr, x = 2, 3-OAr; x = 3, 4) were developed, featuring photoluminescence quantum yields up to 0.81(2) and lifetimes to 117(1) ns. Although the 4f → 5d absorptive transitions for these complexes were all found at ca. 420 nm, their emission bands exhibited large Stokes shifts with maxima occurring at 553 nm for 1-N, 518 nm for 2-N, 508 nm for 3-N, and 459 nm for 4, featuring yellow, lime-green, green, and blue light, respectively. Combined time-dependent density functional theory (TD-DFT) calculations and spectroscopic studies suggested that the long-lived (2)D excited states of these complexes corresponded to singly occupied 5dz(2) orbitals. The observed difference in the Stokes shifts was attributed to the relaxation of excited states through vibrational processes facilitated by the ligands. The photochemistry of the sterically congested complex 4 was demonstrated by C-C bond forming reaction between 4-fluoroiodobenzene and benzene through an outer sphere electron transfer pathway, which expands the capabilities of cerium photosensitizers beyond our previous results that demonstrated inner sphere halogen atom abstraction reactivity by 1-N.

The hexachlorocerate(III) anion, [CeCl], was found to be a potent photoreductant in acetonitrile solution with an estimated excited-state reduction potential of -3.45 V versus CpFe. Despite a short lifetime of 22.1(1) ns, the anion exhibited a photoluminescence quantum yield of 0.61(4) and fast quenching kinetics toward organohalogens allowing for its application in the photocatalytic reduction of aryl chloride substrates.

Although the past 15 years have witnessed the development of sterically bulky and electron-rich alkylphosphine ligands for palladium-catalyzed cross-couplings with aryl chlorides, examples of palladium catalysts based on either triarylphosphine or bidentate phosphine ligands for efficient room temperature cross-coupling reactions with unactivated aryl chlorides are rare. Herein we report a palladium catalyst based on NiXantphos, a deprotonatable chelating aryldiphosphine ligand, to oxidatively add unactivated aryl chlorides at room temperature. Surprisingly, comparison of an extensive array of ligands revealed that under the basic reaction conditions the resultant heterobimetallic Pd–NiXantphos catalyst system outperformed all the other mono- and bidentate ligands in a deprotonative cross-coupling process (DCCP) with aryl chlorides. The DCCP with aryl chlorides affords a variety of triarylmethane products, a class of compounds with various applications and interesting biological activity. Additionally, the DCCP exhibits remarkable chemoselectivity in the presence of aryl chloride substrates bearing heteroaryl groups and sensitive functional groups that are known to undergo 1,2-addition, aldol reaction, and O-, N-, enolate-α-, and C(sp2)–H arylations. The advantages and importance of the Pd–NiXantphos catalyst system outlined herein make it a valuable contribution for applications in Pd-catalyzed arylation reactions with aryl chlorides.