Jeffery A. Bertke

A Motif for Infinite Metal Atom Wires

A new motif for infinite metal atom wires with tunable compositions and properties is developed based on the connection between metal paddlewheel and square planar complex moieties. Two infinite Pd chain compounds, [Pd4(CO)4(OAc)4Pd(acac)2] 1 and [Pd4(CO)4(TFA)4Pd(acac)2] 2, and an infinite Pd-Pt heterometallic chain compound, [Pd4(CO)4(OAc)4Pt(acac)2] 3, are identified by single-crystal X-ray diffraction analysis. In these new structures, the paddlewheel moiety is a Pd four-membered ring coordinated by bridging carboxylic ligands and μ2 carbonyl ligands. The planar moiety is either Pd(acac)2 or Pt(acac)2 (acac = acetylacetonate). These moieties are connected by metallophilic interactions. The results showed that these one-dimensional metal wire compounds have photoluminescent properties that are tunable by changing ligands and metal ions. 3 can also serve as a single source precursor for making Pd4Pt bimetallic nanostructures with precise control of metal composition.

Copper Catalyzed sp3 C–H Etherification with Acyl Protected Phenols

A variety of acyl protected phenols AcOAr participate in sp3 C-H etherification of substrates R-H to give alkyl aryl ethers R-OAr employing tBuOOtBu as oxidant with copper(I) β-diketiminato catalysts [CuI]. Although 1°, 2°, and 3° C-H bonds may be functionalized, selectivity studies reveal a preference for the construction of hindered, 3° C-OAr bonds. Mechanistic studies indicate that β-diketiminato copper(II) phenolates [CuII]-OAr play a key role in this C-O bond forming reaction, formed via transesterification of AcOAr with [CuII]-OtBu intermediates generated upon reaction of [CuI] with tBuOOtBu.

Redox Non-Innocence of Nitrosobenzene at Nickel

Nitrosobenzene (PhNO) serves as a stable analogue of nitroxyl (HNO), a biologically relevant, redox-active nitric oxide derivative. Capture of nitrosobenzene at the electron-deficient β-diketiminato nickel(I) complex [(i) Pr2 NNF6 ]Ni results in reduction of the PhNO ligand to a (PhNO)(./-) species coordinated to a square planar Ni(II) center in [(i) Pr2 NNF6 ]Ni(η(2) -ONPh). Ligand centered reduction leads to the (PhNO)(2-) moiety bound to Ni(II) supported by XAS studies. Systematic investigation of structure-reactivity patterns of (PhNO)(./-) and (PhNO)(2-) ligands reveals parallels with superoxo (O2 )(./-) and peroxo (O2 )(2-) ligands, respectively, and forecasts reactivity patterns of the more transient HNO ligand.

Elasticity in Macrophage-Synthesized Biocrystals

Supramolecular crystalline assembly constitutes a rational approach to bioengineer intracellular structures. Here, biocrystals of clofazimine (CFZ) that form in vivo within macrophages were measured to have marked curvature. Isolated crystals, however, showed reduced curvature suggesting that intracellular forces bend these drug crystals. Consistent with the ability of biocrystals to elastically deform, the inherent crystal structure of the principal molecular component of the biocrystals-the hydrochloride salt of CFZ (CFZ-HCl)-has a corrugated packing along the (001) face and weak dispersive bonding in multiple directions. These characteristics were previously found to be linked to the elasticity of other organic crystals. Internal stress in bent CFZ-HCl led to photoelastic effects on the azimuthal orientation of polarized light transmittance. We propose that elastic, intracellular crystals can serve as templates to construct functional microdevices with different applications.

Copper(II) Activation of Nitrite: Nitrosation of Nucleophiles and Generation of NO by Thiols

Nitrite (NO2-) and nitroso compounds (E-NO, E = RS, RO, and R2N) in mammalian plasma and cells serve important roles in nitric oxide (NO) dependent as well as NO independent signaling. Employing an electron deficient β-diketiminato copper(II) nitrito complex [Cl2NNF6]Cu(κ2-O2N)·THF, thiols mediate reduction of nitrite to NO. In contrast to NO generation upon reaction of thiols at iron nitrite species, at copper this conversion proceeds through nucleophilic attack of thiol RSH on the bound nitrite in [CuII](κ2-O2N) that leads to S-nitrosation to give the S-nitrosothiol RSNO and copper(II) hydroxide [CuII]-OH. This nitrosation pathway is general and results in the nitrosation of the amine Ph2NH and alcohol tBuOH to give Ph2NNO and tBuONO, respectively. NO formation from thiols occurs from the reaction of RSNO and a copper(II) thiolate [CuII]-SR intermediate formed upon reaction of an additional equiv thiol with [CuII]-OH.

Comparing the 2,2'-Biphenylenedithiophosphinate Binding of Americium with Neodymium and Europium.

Advancing our understanding of the minor actinides (Am, Cm) versus lanthanides is key for developing advanced nuclear-fuel cycles. Herein, we describe the preparation of (NBu4 )Am[S2 P((t) Bu2 C12 H6 )]4 and two isomorphous lanthanide complexes, namely one with a similar ionic radius (i.e., Nd(III) ) and an isoelectronic one (Eu(III) ). The results include the first measurement of an Am-S bond length, with a mean value of 2.921(9) Å, by single-crystal X-ray diffraction. Comparison with the Eu(III) and Nd(III) complexes revealed subtle electronic differences between the complexes of Am(III) and the lanthanides.

Three-Coordinate Copper(II) Aryls: Key Intermediates in C–O Bond Formation

Copper(II) aryl species are proposed key intermediates in Cu-catalyzed cross-coupling reactions. Novel three-coordinate copper(II) aryls [CuII]-C6F5 supported by ancillary β-diketiminate ligands form in reactions between copper(II) alkoxides [CuII]-OtBu and B(C6F5)3. Crystallographic, spectroscopic, and DFT studies reveal geometric and electronic structures of these Cu(II) organometallic complexes. Reaction of [CuII]-C6F5 with the free radical NO(g) results in C-N bond formation to give [Cu](η2-ONC6F5). Remarkably, addition of the phenolate anion PhO- to [CuII]-C6F5 directly affords diaryl ether PhO-C6F5 with concomitant generation of the copper(I) species [CuI](solvent) and {[CuI]-C6F5}-. Experimental and computational analysis supports redox disproportionation between [CuII]-C6F5 and {[CuII](C6F5)(OPh)}- to give {[CuI]-C6F5}- and [CuIII](C6F5)(OPh) unstable toward reductive elimination to [CuI](solvent) and PhO-C6F5.

Synthesis, structure, and photoluminescent behaviour of molecular lanthanide–2-thiophenecarboxylate–2,2′:6′,2′′-terpyridine materials

The preparation of a lanthanide series, with the exception of promethium, incorporating 2,2′:6′,2′′-terpyridine (terpy) and 2-thiophenecarboxylate (TC) functionality has been achieved via hydrothermal reaction conditions. The structures of the crystalline products were determined using single crystal X-ray diffraction and bulk purity was confirmed via powder X-ray diffraction and elemental analysis. The series is comprised of four structure types wherein the effects of the lanthanide contraction are manifested in changes in the coordination number and nuclearity of the complexes. From lanthanum through holmium an isomorphous series of symmetric dimers of the general formula [Ln2(terpy)2(TC)4(μ-TC)2(H2O)2]·nH2O (Ln-1, Ln = La–Ho, excluding Pm) was isolated. Using holmium oxide resulted in the formation of Ho-1 whereas use of the holmium chloride precursor resulted in the formation of [Ho2(terpy)2(TC)3(μ-TC)2(H2O)2]TC (Ho-2), that consists of an asymmetric dimer. Beyond Ho, Er–Lu were found to form compounds of the general formula [Ln(terpy)(TC)3(H2O)], the structures of which consist of monomeric units. While Er adopts Er-3, Tm–Lu adopt another structure type (Ln-4, where Ln = Tm, Yb, and Lu), the latter arising from differences in intramolecular hydrogen bonding interactions as well as π–π stacking interactions. The luminescent behaviour of the solid samples was examined and showed ligand-sensitized metal-based visible (Sm, Eu Tb, Dy) and NIR (Nd, Sm, and Yb) emission, with lifetimes up to hundreds of microseconds for select samples. Quantum yields of the visible light emitters have been measured and are additionally presented.

Quantitative Analysis of Different Formation Modes of Platinum Nanocrystals Controlled by Ligand Chemistry

Well-defined metal nanocrystals play important roles in various fields, such as catalysis, medicine, and nanotechnology. They are often synthesized through kinetically controlled process in colloidal systems that contain metal precursors and surfactant molecules. The chemical functionality of surfactants as coordinating ligands to metal ions however remains a largely unsolved problem in this process. Understanding the metal-ligand complexation and its effect on formation kinetics at the molecular level is challenging but essential to the synthesis design of colloidal nanocrystals. Herein we report that spontaneous ligand replacement and anion exchange control the form of coordinated Pt-ligand intermediates in the system of platinum acetylacetonate [Pt(acac)2], primary aliphatic amine, and carboxylic acid ligands. The formed intermediates govern the formation mode of Pt nanocrystals, leading to either a pseudo two-step or a one-step mechanism by switching on or off an autocatalytic surface growth. This finding shows the importance of metal-ligand complexation at the prenucleation stage and represents a critical step forward for the designed synthesis of nanocrystal-based materials.

A Dinitrogen Dicopper(I) Complex via a Mixed‐Valence Dicopper Hydride

Low-temperature reaction of the tris(pyrazolyl)borate copper(II) hydroxide [(iPr2) TpCu]2 (μ-OH)2 with triphenylsilane under a dinitrogen atmosphere gives the bridging dinitrogen complex [(iPr2) TpCu]2 (μ-1,2-N2 ) (3). X-ray crystallography reveals an only slightly activated N2 ligand (N-N: 1.111(6) Å) that bridges between two monovalent (iPr2) TpCu fragments. While DFT studies of mono- and dinuclear copper dinitrogen complexes suggest weak π-backbonding between the d(10) Cu(I) centers and the N2 ligand, they reveal a degree of cooperativity in the dinuclear Cu-N2 -Cu interaction. Addition of MeCN, CNAr(2,6-Me) , or O2 to 3 releases N2 with formation of (iPr2) TpCu(L) (L=NCMe, CNAr(2,6-Me2) ) or [(iPr2) TpCu]2 (μ-η(2) :η(2) -O2 ) (1). Addition of triphenylsilane to [(iPr2) TpCu]2 (μ-OH)2 in pentane allows isolation of a key intermediate [(iPr2) TpCu]2 (μ-H) (5). Although 5 thermally decays under N2 to give 3, it reduces unsaturated substrates, such as CO and HC≡CPh to HC(O)H and H2 C=CHPh, respectively.