Inducing Circularly Polarized Single-Photon Emission via Chiral-Induced Spin Selectivity.

One of the central aims of the field of spintronics is the control of individual electron spins to effectively manage the transmission of quantized data. One well-known mechanism for controlling electronic spin transport is the chiral-induced spin-selectivity (CISS) effect in which a helical nanostructure imparts a preferential spin orientation on the electronic transport. One potential application of the CISS effect is as a transduction pathway between electronic spin and circularly polarized light within nonreciprocal photonic devices. In this work, we identify and quantify the degree of chiral-induced spin-selective electronic transport in helical polyaniline films using magnetoconductive atomic force microscopy (mcAFM). We then induce circularly polarized quantum light emission from CdSe/CdS core/shell quantum dots placed on these films, demonstrating a degree of circular polarization of up to ∼21%. Utilizing time-resolved photoluminescence microscopy, we measure the radiative lifetime difference associated with left- and right-handed circular polarizations of single emitters. These lifetime differences, in combination with Kelvin probe mapping of the variation of surface potential with magnetization of the substrate, help establish an energy level diagram describing the spin-dependent transport pathways that enable the circularly polarized photoluminescence.

Room-Temperature Fiber-Coupled Single-Photon Sources based on Colloidal Quantum Dots and SiV Centers in Back-Excited Nanoantennas.

We demonstrate an important step toward on-chip integration of single-photon sources at room temperature. Excellent photon directionality is achieved with a hybrid metal-dielectric bullseye antenna, while back-excitation is permitted by placement of the emitter in a subwavelength hole positioned at its center. The unique design enables a direct back-excitation and very efficient front coupling of emission either to a low numerical aperture (NA) optics or directly to an optical fiber. To show the versatility of the concept, we fabricate devices containing either a colloidal quantum dot or a nanodiamond containing silicon-vacancy centers, which are accurately positioned using two different nanopositioning methods. Both of these back-excited devices display front collection efficiencies of ∼70% at NAs as low as 0.5. The combination of back-excitation with forward directionality enables direct coupling of the emitted photons into a proximal optical fiber without any coupling optics, thereby facilitating and simplifying future integration.

Direct metal-carbon bonding in symmetric bis(C-H) agostic nickel(i) complexes.

Agostic interactions are examples of σ-type interactions, typically resulting from interactions between C-H σ-bonds with empty transition metal d orbitals. Such interactions often reflect the first step in transition metal-catalysed C-H activation processes and thus are of critical importance in understanding and controlling σ bond activation chemistries. Herein, we report on the unusual electronic structure of linear electron-rich d9 Ni(i) complexes with symmetric bis(C-H) agostic interactions. A combination of Ni K edge and L edge XAS with supporting TD-DFT/DFT calculations reveals an unconventional covalent agostic interaction with limited contributions from the valence Ni 3d orbitals. The agostic interaction is driven via the empty Ni 4p orbitals. The surprisingly strong Ni 4p-derived agostic interaction is dominated by σ contributions with minor π contributions. The resulting ligand-metal donation occurs directly along the C-Ni bond axis, reflecting a novel mode of bis-agostic bonding.

Platinum complexes of a boron-rich diphosphine ligand.

Herein, we describe the preparation, characterization, and reactivity of two PtII bis-hydrocarbyl complexes containing the 1,2-bis(di(3-dicyclohexylboraneyl)propylphosphino)ethane (P2BCy4) ligand. These scaffolds are readily accessed from four-fold hydroboration of 1,2-bis(diallylphosphino)ethane PtII precursors. The electrophilcity of such frameworks is showcased by facile coordination of the strong Lewis base, 4-N,N-dimethylaminopyridine (DMAP). Thermolysis reactions of [Pt(P2BCy4)(R)2] (R = CH3 or Ph) show enhanced (and divergent) reactivity when compared to their "all-alkyl" diphosphine counterparts, implicating involvement of the pendant borane groups. This behaviour is attenuated by protection of these units with DMAP.

Impact of Oxidation State on Reactivity and Selectivity Differences between Nickel(III) and Nickel(IV) Alkyl Complexes.

Described is a systematic comparison of factors impacting the relative rates and selectivities of C(sp3 )-C and C(sp3 )-O bond-forming reactions at high-valent Ni as a function of oxidation state. Two Ni complexes are compared: a cationic octahedral NiIV complex ligated by tris(pyrazolyl)borate and a cationic octahedral NiIII complex ligated by tris(pyrazolyl)methane. Key features of reactivity/selectivity are revealed: 1) C(sp3 )-C(sp2 ) bond-forming reductive elimination occurs from both centers, but the NiIII complex reacts up to 300-fold faster than the NiIV , depending on the reaction conditions. The relative reactivity is proposed to derive from ligand dissociation kinetics, which vary as a function of oxidation state and the presence/absence of visible light. 2) Upon the addition of acetate (AcO- ), the NiIV complex exclusively undergoes C(sp3 )-OAc bond formation, while the NiIII analogue forms the C(sp3 )-C(sp2 ) coupled product selectively. This difference is rationalized based on the electrophilicity of the respective M-C(sp3 ) bonds, and thus their relative reactivity towards outer-sphere SN 2-type bond-forming reactions.

Role of Phosphine Sterics in Strained Aminophosphine Chelate Formation.

The preparation of four-membered aminophosphine (PN) chelates from common metal precursors has largely evaded realization because of the ring strain associated with these species. We report a straightforward approach to the synthesis of such PN metallacycles using simple α-PN ligands analogous to the popular class of small-bite-angle diphosphinomethane ligands. It is demonstrated that bulky phosphine substituents are important to the formation of these chelates.

Oxidation State Dependent Coordination Modes: Accessing an Amidate-Supported Nickel(I) δ-bis(C-H) Agostic Complex.

Amidate-supported two- and three-coordinate NiI complexes were synthesized by reduction of the corresponding NiII precursors. A dramatic change in binding mode is observed upon reduction from NiII to NiI . The NiI derivatives include an unprecedented NiI bis(C-H) agostic complex and a two-coordinate NiI complex.

Phosphoramidate-Supported Cp*Ir(III) Aminoborane H2 B=NR2 Complexes: Synthesis, Structure, and Solution Dynamics.

Reaction of aminoboranes H2 B=NR2 (R=iPr or Cy) with the cationic Cp*Ir(III) phosphoramidate complex [IrCp*{κ(2) -N,O-Xyl(N)P(O)(OEt)2 }][BAr(F) 4 ] generates the aminoborane complexes [IrCp*(H){κ(1) -N-η(2) -HB-Xyl(N)P(OBHNR2 )(OEt)2 }][BAr(F) 4 ] (R=iPr or Cy) in which coordination of a P=O bond with boron weakens the B=N multiple bond. For these complexes, solution- and solid-state, as well as DFT computational techniques, have been employed to substantiate B-N bond rotation of the coordinated aminoborane.

Even the normal is abnormal: N-heterocyclic carbene C(2) binding to a phosphaalkene without breaking the P=C π-bond.

The reaction of MesP=CPh2 with the least sterically demanding N-heterocyclic carbene (NHC = IMe) results in formation of the 'abnormal' (C(4)-substituted) 4-phosphino-NHC (1). In contrast, reaction with Me2IMe gives the unprecedented 'normal' C(2) adduct, Me2IMe → P(Mes)=CPh2 (2). Particularly striking is the asymmetric and weak bonding of the NHC to the P=C moiety in 2. DFT calculations indicate that the P=C natural bond order in 2 (1.54) still reflects significant π-character to the bond (cf. MesP=CPh2: NBO = 1.98). Further computational analysis suggests that π-delocalization into the remote C-phenyl substituents is key to stabilizing the NHC adduct.

Exclusive Csp(3)-Csp(3) vs Csp(2)-Csp(3) Reductive Elimination from Pt(IV) Governed by Ligand Constraints.

Selective reductive elimination of ethane (Csp(3)-Csp(3) RE) was observed following bromide abstraction and subsequent thermolysis of a Pt(IV) complex bearing both Csp(3)- and Csp(2)-hybridized hydrocarbyl ligands. Through a comparative experimental and theoretical study with two other Pt(IV) complexes featuring greater conformational flexibility of the ligand scaffold, we show that the rigidity of a meridionally coordinating ligand raises the barrier for Csp(2)-Csp(3) RE, resulting in unprecedented reactivity.

Synthesis of 2-Nickela(II)oxetanes from Nickel(0) and Epoxides: Structure, Reactivity, and a New Mechanism of Formation.

2-Nickelaoxetanes have been frequently invoked as reactive intermediates in catalytic reactions of epoxides using nickel, but have never been isolated or experimentally observed in these transformations. Herein, we report the preparation of a series of well-defined nickelaoxetanes formed via the oxidative addition of nickel(0) with epoxides featuring ketones. The stereochemistry of the products is retained, which has not yet been reported for nickelaoxetanes. Theoretical calculations support a bimetallic ring-opening/closing pathway over a concerted oxidative addition. Initial reactivity studies of a nickelaoxetane demonstrated protonolysis, oxidatively induced reductive elimination, deoxygenation, and elimination reactions when treated with the appropriate reagents.