Organometallic Chirality Sensing via "Click"-Like η6-Arene Coordination with an Achiral Cp*Ru(II) Piano Stool Complex.

Piano stool complexes have been studied over many years and found widespread applications in organic synthesis, catalysis, materials and drug development. We now report the first examples of quantitative chiroptical molecular recognition of chiral compounds through click-like η6-arene coordination with readily available half sandwich complexes. This conceptually new approach to chirality sensing is based on irreversible acetonitrile displacement of [Cp*Ru(CH3CN)3]PF6 by an aromatic target molecule, a process that is fast and complete within a few minutes at room temperature. The metal coordination coincides with characteristic circular dichroism inductions that can be easily correlated to the absolute configuration and enantiomeric ratio of the bound molecule. A relay assay that decouples the determination of the enantiomeric composition and of the total sample amount by a practical CD/UV measurement protocol was developed and successfully tested. The introduction of piano stool complexes to the chiroptical sensing realm is mechanistically unique and extends the scope of currently known methods with small-molecule probes that require the presence of amino, alcohol, carboxylate or other privileged functional groups for binding of the target compound. A broad application range including pharmaceutically relevant multifunctional molecules and the use in chromatography-free asymmetric reaction analysis are also demonstrated.

Organocatalytic Asymmetric Conjugate Addition of Fluorooxindoles to Quinone Methides.

Fluorooxindoles undergo asymmetric Michael addition to para-quinone methides under phase-transfer conditions with 10 mol% of a readily available cinchona alkaloid ammonium catalyst. This reaction affords sterically encumbered, multifunctional fluorinated organic compounds displaying two adjacent chirality centers with high yields, ee's and dr's.

General alkyl fluoride functionalization via short-lived carbocation-organozincate ion pairs.

Fluorinated organic compounds are frequently used across the chemical and life sciences. Although a large, structurally diverse pool of alkyl fluorides is nowadays available, synthetic applications trail behind the widely accepted utility of other halides. We envisioned that C(sp2)-C(sp3) cross-coupling reactions of alkyl fluorides with fluorophilic organozinc compounds should be possible through a heterolytic mechanism that involves short-lived ion pairs and uses the stability of the Zn-F bond as the thermodynamic driving force. This would be mechanistically different from previously reported radical reactions and overcome long-standing limitations of organometallic cross-coupling methodology, including competing ß-hydride elimination, homodimerization and hydrodefluorination. Here, we show a practical Csp3-F bond functionalization method that expands the currently restricted synthetic space of unactivated primary, secondary and tertiary C(sp3)-F bonds but also uses benzylic, propargylic and acyl fluorides. Many functional groups and sterically demanding substrates are tolerated, which allows practical carbon-carbon bond formation and late-stage functionalization.

Alkaline earth metal-assisted dinitrogen activation at nickel.

Rare examples of trinuclear [Ni-N2-M-N2-Ni] core (M = Ca, Mg) with linear bridged dinitrogen ligands are reported in this work. The reduction of [iPr2NN]Ni(µ-Br)2Li(thf)2 (1) (iPr2NN = 2,4-bis-(2,6-diisopropylphenylimido)pentyl) with elemental Mg or Ca in THF under an atmosphere of dinitrogen yields the complex {iPr2NNNi(µ-N2)}2M (thf)4 (M = Mg, complex 2 and M = Ca, complex 3). The bridging end-on (µ-N2)2M(thf)4 moiety connects the two [iPr2NNNi]- nickelate fragments. A combination of X-ray crystallography, solution and solid-state spectroscopy have been applied to characterize complexes 2 and 3, and DFT studies have been used to help explain the bonding and electronic structure in these unique Ni-N2-Mg and Ni-N2-Ca complexes.

Synthesis and Characterization of Cerium-Oxo Clusters Capped by Acetylacetonate.

Cerium-oxo clusters have applications in fields ranging from catalysis to electronics and also hold the potential to inform on aspects of actinide chemistry. Toward this end, a cerium-acetylacetonate (acac1-) monomeric molecule, Ce(acac)4 (Ce-1), and two acac1--decorated cerium-oxo clusters, [Ce10O8(acac)14(CH3O)6(CH3OH)2]·10.5MeOH (Ce-10) and [Ce12O12(OH)4(acac)16(CH3COO)2]·6(CH3CN) (Ce-12), were prepared and structurally characterized. The Ce(acac)4 monomer contains CeIV. Crystallographic data and bond valence summation values for the Ce-10 and Ce-12 clusters are consistent with both clusters having a mixture of CeIII and CeIV cations. Ce L3-edge X-ray absorption spectroscopy, performed on Ce-10, showed contributions from both CeIII and CeIV. The Ce-10 cluster is built from a hexameric cluster, with six CeIV sites, that is capped by two dimeric CeIII units. By comparison, Ce-12, which formed upon dissolution of Ce-10 in acetonitrile, consists of a central decamer built from edge sharing CeIV hexameric units, and two monomeric CeIII sites that are bound on the outer corners of the inner Ce10 core. Electrospray ionization mass spectrometry data for solutions prepared by dissolving Ce-10 in acetonitrile showed that the major ions could be attributed to Ce10 clusters that differed primarily in the number of acac1-, OH1-, MeO1-, and O2- ligands. Small angle X-ray scattering measurements for Ce-10 dissolved in acetonitrile showed structural units slightly larger than either Ce10 or Ce12 in solution, likely due to aggregation. Taken together, these results suggest that the acetylacetonate supported clusters can support diverse solution-phase speciation in organic solutions that could lead to stabilization of higher order cerium containing clusters, such as cluster sizes that are greater than the Ce10 and Ce12 reported herein.

Thiol and H2S-Mediated NO Generation from Nitrate at Copper(II).

Reduction of nitrate is an essential, yet challenging chemical task required to manage this relatively inert oxoanion in the environment and biology. We show that thiols, ubiquitous reductants in biology, convert nitrate to nitric oxide at a Cu(II) center under mild conditions. The ß-diketiminato complex [Cl2NNF6]Cu(κ2-O2NO) engages in O-atom transfer with various thiols (RSH) to form the corresponding copper(II) nitrite [CuII](κ2-O2N) and sulfenic acid (RSOH). The copper(II) nitrite further reacts with RSH to give S-nitrosothiols RSNO and [CuII]2(µ-OH)2 en route to NO formation via [CuII]-SR intermediates. The gasotransmitter H2S also reduces nitrate at copper(II) to generate NO, providing a lens into NO3-/H2S crosstalk. The interaction of thiols with nitrate at copper(II) releases a cascade of N- and S-based signaling molecules in biology.

Electrocatalytic Ammonia Oxidation by a Low-Coordinate Copper Complex.

Molecular catalysts for ammonia oxidation to dinitrogen represent enabling components to utilize ammonia as a fuel and/or source of hydrogen. Ammonia oxidation requires not only the breaking of multiple strong N-H bonds but also controlled N-N bond formation. We report a novel ß-diketiminato copper complex [iPr2NNF6]CuI-NH3 ([CuI]-NH3 (2)) as a robust electrocatalyst for NH3 oxidation in acetonitrile under homogeneous conditions. Complex 2 operates at a moderate overpotential (η = 700 mV) with a TOFmax = 940 h-1 as determined from CV data in 1.3 M NH3-MeCN solvent. Prolonged (>5 h) controlled potential electrolysis (CPE) reveals the stability and robustness of the catalyst under electrocatalytic conditions. Detailed mechanistic investigations indicate that electrochemical oxidation of [CuI]-NH3 forms {[CuII]-NH3}+ (4), which undergoes deprotonation by excess NH3 to form reactive copper(II)-amide ([CuII]-NH2, 6) unstable toward N-N bond formation to give the dinuclear hydrazine complex [CuI]2(µ-N2H4). Electrochemical studies reveal that the diammine complex [CuI](NH3)2 (7) forms at high ammonia concentration as part of the {[CuII](NH3)2}+/[CuI](NH3)2 redox couple that is electrocatalytically inactive. DFT analysis reveals a much higher thermodynamic barrier for deprotonation of the four-coordinate {[CuII](NH3)2}+ (8) by NH3 to give the copper(II) amide [CuII](NH2)(NH3) (9) (ΔG = 31.7 kcal/mol) as compared to deprotonation of the three-coordinate {[CuII]-NH3}+ by NH3 to provide the reactive three-coordinate parent amide [CuII]-NH2 (ΔG = 18.1 kcal/mol) susceptible to N-N coupling to form [CuI]2(µ-N2H4) (ΔG = -11.8 kcal/mol).

Lewis acid-assisted reduction of nitrite to nitric and nitrous oxides via the elusive nitrite radical dianion.

Reduction of nitrite anions (NO2-) to nitric oxide (NO), nitrous oxide (N2O) and ultimately dinitrogen (N2) takes place in a variety of environments, including in the soil as part of the biogeochemical nitrogen cycle and in acidified nuclear waste. Nitrite reduction typically takes place within the coordination sphere of a redox-active transition metal. Here we show that Lewis acid coordination can substantially modify the reduction potential of this polyoxoanion to allow for its reduction under non-aqueous conditions (-0.74 V versus NHE). Detailed characterization confirms the formation of the borane-capped radical nitrite dianion (NO22-), which features a N(II) oxidation state. Protonation of the nitrite dianion results in the facile loss of nitric oxide (NO), whereas its reaction with NO results in disproportionation to nitrous oxide (N2O) and nitrite (NO2-). This system connects three redox levels in the global nitrogen cycle and provides fundamental insights into the conversion of NO2- to NO.

Lanthanide Luminescence and Thermochromic Emission from Soft-Atom Donor Dichalcogenoimidodiphosphinate Ligands.

The luminescence properties of two divalent europium complexes of the type Eu[N(SPPh2)2]2(THF)2 (1) and Eu[N(SePPh2)2]2(THF)2 (2) were investigated. The first complex, Eu[N(SPPh2)2]2(THF)2 (1), was found to be isomorphous with the reported structure of complex 2 and exhibited room temperature luminescence with thermochromic emission upon cooling. We found the complex Eu[N(SePPh2)2]2(THF)2 (2) was also thermochromic but the emission intensity was sensitive to temperature. Both room temperature and low temperature (100 K) single crystal X-ray structural investigation of 1 and 2 indicate geometric distortions of the metal coordination, which may be important for understanding the thermochromic behavior of these complexes. The trivalent europium complex Eu[N(SPPh2)2]3 (3) with the same ligand as 1 was also structurally characterized as a function of temperature and exhibited temperature-dependent luminescence intensity, with no observable emission at room temperature but intense luminescence at 77 K. Variable temperature Raman spectroscopy was used to determine the onset temperature of luminescence of Eu[N(SPPh2)2]3 (3), where the 615 nm (5D0 → 7F2 transition) peak was quenched above 130 K. The UV-visible diffuse reflectance of 3 provides evidence of an LMCT band, supporting a mechanism of thermally activated LMCT quenching of Eu(III) emitting states. A series of ten isomorphous, trivalent lanthanide complexes of type Ln[N(SPPh2)2]3 (Ln = Eu (3) Pr (4), Nd (5), Sm (6), Gd (7), Tb (8)) and Ln[N(SePPh2)2]3 (Ln = Pr (9), Nd (10, structure was previously reported), Sm (11), and Gd (12) for Q = Se) were also synthesized and structurally characterized. These complexes for Ln = Pr, Nd, Sm, and Tb exhibited room temperature luminescence. This study provides examples of temperature-dependent luminescence of both Eu2+ and Eu3+, and the use of soft-atom donor ligands to sensitize lanthanide luminescence in a range of trivalent lanthanides, spanning near IR and visible emitters.

NO Coupling at Copper to cis-Hyponitrite: N2O Formation via Protonation and H-Atom Transfer.

Copper nitrite reductases (CuNIRs) convert NO2- to NO as well as NO to N2O under high NO flux at a mononuclear type 2 Cu center. While model complexes illustrate N-N coupling from NO that results in symmetric trans-hyponitrite [CuII]-ONNO-[CuII] complexes, we report NO assembly at a single Cu site in the presence of an external reductant Cp*2M (M = Co, Fe) to give the first copper cis-hyponitrites [Cp*2M]{[CuII](κ2-O2N2)[CuI]}. Importantly, the κ1-N-bound [CuI] fragment may be easily removed by the addition of mild Lewis bases such as CNAr or pyridine to form the spectroscopically similar anion {[CuII](κ2-O2N2)}-. The addition of electrophiles such as H+ to these anionic copper(II) cis-hyponitrites leads to N2O generation with the formation of the dicopper(II)-bis-µ-hydroxide [CuII]2(µ-OH)2. One-electron oxidation of the {[CuII](κ2-O2N2)}- core turns on H-atom transfer reactivity, enabling the oxidation of 9,10-dihydroanthracene to anthracene with concomitant formation of N2O and [CuII]2(µ-OH)2. These studies illustrate both the reductive coupling of NO at a single copper center and a way to harness the strong oxidizing power of nitric oxide via the neutral cis-hyponitrite [Cu](κ2-O2N2).

NO Generation from the Cross-Talks between Ene-diol Antioxidants and Nitrite at Metal Sites.

The one-electron reduction of nitrite (NO2-) to nitric oxide (NO) and ene-diol oxidation are two important biochemical transformations. Employing mononuclear cobalt-nitrite complexes with CoIII and CoII oxidation states, [(Bz3Tren)CoIII(nitrite)2](ClO4) (1) and [(Bz3Tren)CoII(nitrite)](ClO4) (2), this report illustrates NO release coupled to stepwise oxidation of ene-diol antioxidants such as l-ascorbic acid (AH2) and catechol. Analysis of the AH2 end-product reveals that the reaction with complex 1 affords dehydroascorbic acid. Intriguingly, a controlled oxidation of AH2 with complex 2 results in a [CoII]-bound ascorbyl radical-anion (8). Finally, NO release with the concomitant generation of metal-bound 3,5-di-tert-butyl-semiquinone radical anion from the reactions of 3,5-di-tert-butyl-catechol and [(Bz3Tren)MII(nitrite)](ClO4) (2, M = Co; 4, M = Zn) provides mechanistic insights into the cross-talk between nitrite and ene-diols at the metal sites.

Reactivity of a Chloride Decorated, Mixed Valent CeIII/IV38-Oxo Cluster.

A cerium-oxo nanocluster capped by chloride ligands, [CeIV38-nCeIIInO56-(n+1)(OH)n+1Cl51(H2O)11]10- (n = 1-24), has been isolated from acidic chloride solutions by using potassium counterions. The crystal structure was elucidated using single crystal X-ray diffraction. At the center of the cluster is a {Ce14} core that exhibits the same fluorite-type structure as bulk CeO2, with eight-coordinate Ce sites bridged by tetrahedral oxo anions. The {Ce14} is further surrounded by a peripheral shell of six tetranuclear {Ce4} subunits that are located on each of the faces of the core to yield the {Ce38} cluster. The surface of the cluster is capped by 51 bridging/terminal chloride ligands and 11 water molecules; the anionic cluster is charge balanced by potassium counterions that exist in the outer coordination sphere. While assignment of the Ce oxidation state by bond valence summation was ambiguous, Ce L3-edge X-ray absorption, X-ray photoelectron, and UV-vis-NIR absorption results were consistent with a CeIII/CeIV cluster. Systematic changes in the XANES and UV-vis-NIR absorption spectra over time pointed to reactivity of the cluster upon exposure to air. These changes were examined using single crystal X-ray diffraction, and a clear single-crystal-to-single-crystal transformation was captured; an overall loss of surface-bound chlorides and water molecules as well as new µ2-OH sites was observed on the cluster surface. This work provides a rare snapshot of metal oxide cluster reactivity. The results may hold implications for understanding the physical and chemical properties of ceria nanoparticles and provide insight into the behavior of other metal-oxo clusters of significant technological and environmental interest.

Harnessing Bismuth Coordination Chemistry to Achieve Bright, Long-Lived Organic Phosphorescence.

A new bismuth(III)-organic compound, Hphen[Bi2(HPDC)2(PDC)2(NO3)]·4H2O (Bi-1; PDC = 2,6-pyridinedicarboxylate and phen = 1,10-phenanthroline), was synthesized, and the structure was determined by single-crystal X-ray diffraction. The compound was found to display bright-blue-green phosphorescence in the solid state under UV irradiation, with a luminescent lifetime of 1.776 ms at room temperature. The room temperature and low-temperature (77 K) emission spectra exhibited the vibronic structure characteristic of Hphen phosphorescence. Time-dependent density functional theory studies showed that the excitation pathway arises from an energy transfer from the dimeric structural unit to Hphen, with participation from a nine-coordinate Bi center. The triplet state of Hphen is believed to be stabilized via supramolecular interactions, which, when coupled with the heavy-atom effect induced by Bi, leads to the observed long-lived luminescence. The compound displayed a solid-state quantum yield of over 27%. To the best of our knowledge, this is the first such compound to exhibit phenanthrolinium phosphorescence with such long-lived, room temperature lifetimes in the solid state. To further elucidate the energy-transfer mechanism, Ln3+ (Ln = Eu, Tb, Sm) ions were successfully doped into the parent compound, and the resulting materials exhibited dual emission from Hphen and Ln, promoting tunability of the emission color.

Uncovering Redox Non-innocent Hydrogen-Bonding in Cu(I)-Diazene Complexes.

The life-sustaining reduction of N2 to NH3 is thermoneutral yet kinetically challenged by high-energy intermediates such as N2H2. Exploring intramolecular H-bonding as a potential strategy to stabilize diazene intermediates, we employ a series of [xHetTpCu]2(µ-N2H2) complexes that exhibit H-bonding between pendant aromatic N-heterocycles (xHet) such as pyridine and a bridging trans-N2H2 ligand at copper(I) centers. X-ray crystallography and IR spectroscopy clearly reveal H-bonding in [pyMeTpCu]2(µ-N2H2) while low-temperature 1H NMR studies coupled with DFT analysis reveals a dynamic equilibrium between two closely related, symmetric H-bonded structural motifs. Importantly, the xHet pendant negligibly influences the electronic structure of xHetTpCuI centers in xHetTpCu(CNAr2,6-Me2) complexes that lack H-bonding as judged by nearly indistinguishable ν(CN) frequencies (2113-2117 cm-1). Nonetheless, H-bonding in the corresponding [xHetTpCu]2(µ-N2H2) complexes results in marked changes in ν(NN) (1398-1419 cm-1) revealed through resonance Raman studies. Due to the closely matched N-H BDEs of N2H2 and the pyH0 cation radical, the aromatic N-heterocyclic pendants may encourage partial H-atom transfer (HAT) from N2H2 to xHet through redox-non-innocent H-bonding in [xHetTpCu]2(µ-N2H2). DFT studies reveal modest thermodynamic barriers for concerted transfer of both H-atoms of coordinated N2H2 to the xHet pendants to generate tautomeric [xHetHTpCu]2(µ-N2) complexes, identifying metal-assisted concerted dual HAT as a thermodynamically favorable pathway for N2/N2H2 interconversion.

Mechanism of O-Atom Transfer from Nitrite: Nitric Oxide Release at Copper(II).

Nitric oxide (NO) is a key signaling molecule in health and disease. While nitrite acts as a reservoir of NO activity, mechanisms for NO release require further understanding. A series of electronically varied ß-diketiminatocopper(II) nitrite complexes [CuII](κ2-O2N) react with a range of electronically tuned triarylphosphines PArZ3 that release NO with the formation of O═PArZ3. Second-order rate constants are largest for electron-poor copper(II) nitrite and electron-rich phosphine pairs. Computational analysis reveals a transition-state structure energetically matched with experimentally determined activation barriers. The production of NO follows a pathway that involves nitrite isomerization at CuII from κ2-O2N to κ1-NO2 followed by O-atom transfer (OAT) to form O═PArZ3 and [CuI]-NO that releases NO upon PArZ3 binding at CuI to form [CuI]-PArZ3. These findings illustrate important mechanistic considerations involved in NO formation from nitrite via OAT.

Structure-Property Relationships in Photoluminescent Bismuth Halide Organic Hybrid Materials.

Seven novel bismuth(III)-halide phases, Bi2Cl6(terpy)2·0.5(H2O) (1), Bi2Cl4(terpy)2(k2-TC)2(2) (TC = 2-thiophene monocarboxylate), BiCl(terpy)(k2-TC)2 (3A-Cl), BiBr(terpy)(k2-TC)2 (3A-Br), BiCl(terpy)(k2-TC)2 (3B-Cl), [BiCl(terpy)(k2-TC)2][Bi(terpy)(k2-TC)3]·0.55(TCA) (4), [BiBr3(terpy)(MeOH)] (5), and [BiBr2(terpy)(k2-TC)][BiBr1.16(terpy)(k2-TC)1.84] (6), were prepared under mild synthetic conditions from methanolic/aqueous solutions containing BiX3 (X = Cl, Br) and 2,2':6',2″-terpyridine (terpy) and/or 2-thiophene monocarboxylic acid (TCA). A heterometallic series, 3A-Bi1-xEuxCl, with the general formula Bi1-xEuxCl(terpy)(k2-TC)2 (x = 0.001, 0.005, 0.01, 0.05) was also prepared through trace Eu doping of the 3A-Cl phase. The structures were determined through single-crystal X-ray diffraction and are built from a range of molecular units including monomeric and dimeric complexes. The solid-state photoluminescent properties of the compounds were examined through steady-state and time-resolved methods. While the homometallic phases exhibited broad green to yellow emission, the heterometallic phases displayed yellow, orange, and red emission that can be attributed to the simultaneous ligand/Bi-halide and Eu centered emissions. Photoluminescent color tuning was achieved by controlling the relative intensities of these concurrent emissions through compositional modifications including the Eu doping percentage. Notably, all emissive homo- and heterometallic phases exhibited rare visible excitation pathways that based on theoretical quantum mechanical calculations are attributed to halide-metal to ligand charge transfer (XMLCT). Through a combined experimental and computational approach, fundamental insight into the structure-property relationships within these Bi halide organic hybrid materials is provided.

Thionitrite and Perthionitrite in NO Signaling at Zinc.

NO and H2 S serve as signaling molecules in biology with intertwined reactivity. HSNO and HSSNO with their conjugate bases - SNO and - SSNO form in the reaction of H2 S with NO as well as S-nitrosothiols (RSNO) and nitrite (NO2- ) that serve as NO reservoirs. While HSNO and HSSNO are elusive, their conjugate bases form isolable zinc complexes Ph,Me TpZn(SNO) and Ph,Me TpZn(SSNO) supported by tris(pyrazolyl)borate ligands. Reaction of Na(15-C-5)SSNO with Ph,Me TpZn(ClO4 ) provides Ph,Me TpZn(SSNO) that undergoes S-atom removal by PEt3 to give Ph,Me TpZn(SNO) and S=PEt3 . Unexpectedly stable at room temperature, these Zn-SNO and Zn-SSNO complexes release NO upon heating. Ph,Me TpZn(SNO) and Ph,Me TpZn(SSNO) quickly react with acidic thiols such as C6 F5 SH to form N2 O and NO, respectively. Increasing the thiol basicity in p-substituted aromatic thiols 4-X ArSH in the reaction with Ph,Me TpZn(SNO) turns on competing S-nitrosation to form Ph,Me TpZn-SH and RSNO, the latter a known precursor for NO.

Impact of Noncovalent Interactions on the Structural Chemistry of Thorium(IV)-Aquo-Chloro Complexes.

Five novel tetravalent thorium (Th) compounds that consist of Th(H2O)xCly structural units were isolated from acidic aqueous solutions using a series of nitrogen-containing heterocyclic hydrogen (H) bond donors. Taken together with three previously reported phases, the compounds provide a series of monomeric ThIV complexes wherein the effects of noncovalent interactions (and H-bond donor identity) on Th structural chemistry can be examined. Seven distinct structural units of the general formulas [Th(H2O)xCl8-x]x-4 (x = 2, 4) and [Th(H2O)xCl9-x]x-5 (x = 5-7) are described. The complexes range from chloride-deficient [Th(H2O)7Cl2]2+ to chloride-rich [Th(H2O)2Cl6]2- species, and theory was used to understand the relative energies that separate complexes within this series via the stepwise chloride addition to an aquated Th cation. Electronic structure theory predicted the reaction energies of chloride addition and release of water through a series of transformations, generally highlighting an energetic driving force for chloride complexation. To probe the role of the counterion in the stabilization of these complexes, electrostatic potential (ESP) surfaces were calculated. The ESP surfaces indicated a dependence of the chloride distribution about the Th metal center on the pKa of the countercation, highlighting the directing effects of noncovalent interactions (e.g., Hbonding) on Th speciation.

Copper(ii) ketimides in sp3 C-H amination.

Commercially available benzophenone imine (HN[double bond, length as m-dash]CPh2) reacts with ß-diketiminato copper(ii) tert-butoxide complexes [CuII]-O t Bu to form isolable copper(ii) ketimides [CuII]-N[double bond, length as m-dash]CPh2. Structural characterization of the three coordinate copper(ii) ketimide [Me3NN]Cu-N[double bond, length as m-dash]CPh2 reveals a short Cu-Nketimide distance (1.700(2) Å) with a nearly linear Cu-N-C linkage (178.9(2)°). Copper(ii) ketimides [CuII]-N[double bond, length as m-dash]CPh2 readily capture alkyl radicals R˙ (PhCH(˙)Me and Cy˙) to form the corresponding R-N[double bond, length as m-dash]CPh2 products in a process that competes with N-N coupling of copper(ii) ketimides [CuII]-N[double bond, length as m-dash]CPh2 to form the azine Ph2C[double bond, length as m-dash]N-N[double bond, length as m-dash]CPh2. Copper(ii) ketimides [CuII]-N[double bond, length as m-dash]CAr2 serve as intermediates in catalytic sp3 C-H amination of substrates R-H with ketimines HN[double bond, length as m-dash]CAr2 and t BuOO t Bu as oxidant to form N-alkyl ketimines R-N[double bond, length as m-dash]CAr2. This protocol enables the use of unactivated sp3 C-H bonds to give R-N[double bond, length as m-dash]CAr2 products easily converted to primary amines R-NH2 via simple acidic deprotection.

Three-Coordinate Copper(II) Alkynyl Complex in C-C Bond Formation: The Sesquicentennial of the Glaser Coupling.

Copper(II) alkynyl species are proposed as key intermediates in numerous Cu-catalyzed C-C coupling reactions. Supported by a ß-diketiminate ligand, the three-coordinate copper(II) alkynyl [CuII]-C≡CAr (Ar = 2,6-Cl2C6H3) forms upon reaction of the alkyne H-C≡CAr with the copper(II) tert-butoxide complex [CuII]-OtBu. In solution, this [CuII]-C≡CAr species cleanly transforms to the Glaser coupling product ArC≡C-C≡CAr and [CuI](solvent). Addition of nucleophiles R'C≡C-Li (R' = aryl, silyl) and Ph-Li to [CuII]-C≡CAr affords the corresponding Csp-Csp and Csp-Csp2 coupled products RC≡C-C≡CAr and Ph-C≡CAr with concomitant generation of [CuI](solvent) and {[CuI]-C≡CAr}-, respectively. Supported by density functional theory (DFT) calculations, redox disproportionation forms [CuIII](C≡CAr)(R) species that reductively eliminate R-C≡CAr products. [CuII]-C≡CAr also captures the trityl radical Ph3C· to give Ph3C-C≡CAr. Radical capture represents the key Csp-Csp3 bond-forming step in the copper-catalyzed C-H functionalization of benzylic substrates R-H with alkynes H-C≡CR' (R' = (hetero)aryl, silyl) that provide Csp-Csp3 coupled products R-C≡CR via radical relay with tBuOOtBu as oxidant.