A Dye-Sensitized Sensor for Oxygen Detection under Visible Light.

Sensors that can accurately assess oxygen (O) concentrations in real time are crucial for a wide range of applications spanning personal health monitoring, environmental protection, and industrial process development. Here a high-performance chemiresistive sensor that allows for the rapid detection of O at room temperature under visible light illumination is described. Inspired by the operating principles of dye-sensitized solar cells, the chemiresistor is based on a single-walled carbon nanotube-titania hybrid (SWCNT-TiO) bearing a molecular Re-based photosensitizer [(bpy)(CO)ReBr] (bpy = 4,4'-[P(O)(OH)]-2,2'-bipyridine).

Triphenylphosphine Oxide: A Versatile Covalent Functionality for Carbon Nanotubes.

Broadening the scope of functionalities that can be covalently bound to single-walled carbon nanotubes (SWCNTs) is crucial for enhancing the versatility of this promising nanomaterial class in applied settings. Here we report the covalent linkage of triphenylphosphine oxide [PhP(O)] to SWCNTs, a hitherto overlooked surface functionality. We detail the synthesis and structural characterization of a new family of phosphine oxide-functionalized diaryliodonium salts that can facilitate direct PhP(O) transfer and afford novel SWCNTs with tunable PhP(O) content (SWCNT-P).

Phosphine Oxide-Functionalized Terthiophene Redox Systems.

Main group systems capable of undergoing controlled redox events at extreme potentials are elusive yet highly desirable for a range of organic electronics applications including use as energy storage media. Herein we describe phosphine oxide-functionalized terthiophenes that exhibit two reversible 1e reductions at potentials below -2 V vs Fc/Fc (Fc=ferrocene) while retaining high degrees of stability. A phosphine oxide-functionalized terthiophene radical anion was synthesized in which the redox-responsive nature of the platform was established using combined structural, spectroscopic, and computational characterization.

Chemiresistive Hydrogen Sensing with Size-Limited Palladium Nanoparticles in Iptycene-Containing Poly(arylene ether)s.

Metal nanoparticles have been widely employed in chemical sensing due to their high reactivity toward various gases. The size of the metal nanoparticles often dictates their reactivity and hence their performance as chemiresistive sensors. Herein, we report that iptycene-containing poly(arylene ether)s (PAEs) have been shown to limit the growth of palladium nanoparticles (Pd NPs) and stabilize the Pd NPs dispersion.

Wireless Lateral Flow Device for Biosensing.

Many biosensing methods rely on signals produced by enzyme-catalyzed reactions and efficient methods to detect and record this activity. Herein, we report a wireless lateral flow device and demonstrate the conversion of oxidase reactions to changes in the resonance of radio frequency identification (RFID) circuits. The detection is triggered by polyoxometalate-catalyzed oxidative doping of polypyrrole (pPy) when exposed to oxidase-generated HO.

Trace Hydrogen Sulfide Sensing Inspired by Polyoxometalate-Mediated Aerobic Oxidation.

A high-performance chemiresistive gas sensor is described for the detection of hydrogen sulfide (HS), an acutely toxic and corrosive gas. The chemiresistor operates at room temperature with low power requirements potentially suitable for wearable sensors or for rapid in-field detection of HS in settings such as pipelines and wastewater treatment plants. Specifically, we report chemiresistors based on single-walled carbon nanotubes (SWCNTs) containing highly oxidizing platinum-polyoxometalate (Pt-POM) selectors.

A chemiresistive methane sensor.

A chemiresistive sensor is described for the detection of methane (CH), a potent greenhouse gas that also poses an explosion hazard in air. The chemiresistor allows for the low-power, low-cost, and distributed sensing of CH at room temperature in air with environmental implications for gas leak detection in homes, production facilities, and pipelines. Specifically, the chemiresistors are based on single-walled carbon nanotubes (SWCNTs) noncovalently functionalized with poly(4-vinylpyridine) (P4VP) that enables the incorporation of a platinum-polyoxometalate (Pt-POM) CH oxidation precatalyst into the sensor by P4VP coordination.

Hydrogenation of -Heteroarenes Using Rhodium Precatalysts: Reductive Elimination Leads to Formation of Multimetallic Clusters.

A rhodium-catalyzed method for the hydrogenation of -heteroarenes is described. A diverse array of unsubstituted -heteroarenes including pyridine, pyrrole, and pyrazine, traditionally challenging substrates for hydrogenation, were successfully hydrogenated using the organometallic precatalysts, [(η-CMe)Rh(N-C)H] (N-C = 2-phenylpyridinyl (ppy) or benzo[]quinolinyl (bq)). In addition, the hydrogenation of polyaromatic -heteroarenes exhibited uncommon chemoselectivity.

Ni(I)-X Complexes Bearing a Bulky α-Diimine Ligand: Synthesis, Structure, and Superior Catalytic Performance in the Hydrogen Isotope Exchange in Pharmaceuticals.

The synthesis and spectroscopic characterization of a family of Ni-X (X = Cl, Br, I, H) complexes supported by the bulky α-diimine chelate N, N'-bis(1 R,2 R,3 R,5 S)-(-)-isopinocampheyl-2,3-butanediimine (ADI) are described. Diimine-supported, three-coordinate nickel(I)-X complexes have been proposed as key intermediates in a host of catalytic transformations such as C-C and C-heteroatom cross-coupling and C-H functionalization but have until now remained synthetically elusive. A combination of structural, spectroscopic, electrochemical, and computational studies were used to establish the electronic structure of each monomeric [(ADI)NiX] (X = Cl, Br, I) complex as a nickel(I) derivative supported by a redox-neutral α-diimine chelate.

Proton-Coupled Electron Transfer to a Molybdenum Ethylene Complex Yields a β-Agostic Ethyl: Structure, Dynamics and Mechanism.

The interconversion of molybdenum ethylene and ethyl complexes by proton-coupled electron transfer (PCET) is described, an unusual transformation in organometallic chemistry. The cationic molybdenum ethylene complex [(Tpy)(PPhMe)Mo(CH)][BArF] ([1-CH]; Tpy = 4'-Ph-2,2',6',2″-terpyridine, ArF = [CH-3,5-(CF)]) was synthesized, structurally characterized, and its electronic structure established by a combination of spectroscopic and computational methods. The overall electronic structure is best described as a molybdenum(III) complex with a metallacyclopropane and a redox neutral terpyridine ligand.

Ultrafast Photophysics of a Dinitrogen-Bridged Molybdenum Complex.

Among the many metal-dinitrogen complexes synthesized, the end-on bridging (μ, η, η-N) coordination mode is notoriously unreactive for nitrogen fixation. This is principally due to the large activation energy for ground-state nitrogen-element bond formation and motivates exploration of the photoexcited reactivity of this coordination mode. To provide the foundation for this concept, the photophysics of a dinitrogen-bridged molybdenum complex was explored by ultrafast electronic spectroscopies.

Selective [1,4]-Hydrovinylation of 1,3-Dienes with Unactivated Olefins Enabled by Iron Diimine Catalysts.

The selective, intermolecular [1,4]-hydrovinylation of conjugated dienes with unactivated α-olefins catalyzed by α-diimine iron complexes is described. Value-added "skipped" diene products were obtained with exclusive [1,4]-selectivity, and the formation of branched, ( Z)-olefin products was observed with no evidence for alkene isomerization. Mechanistic studies conducted with the well-defined, single-component iron precatalyst (DI)Fe(COD) (DI = [2,4,6-Me-CH-N═CMe]); COD = 1,5-cyclooctadiene) provided insights into the origin of the high selectivity.

Interconversion of Molybdenum Imido and Amido Complexes by Proton-Coupled Electron Transfer.

Interconversion of the molybdenum amido [( Tpy)(PPh Me) Mo(NHtBuAr)][BArF ] ( Tpy=4'-Ph-2,2',6',2"-terpyridine; tBuAr=4-tert-butyl-C H ; ArF =(C H -3,5-(CF ) ) ) and imido [( Tpy)(PPh Me) Mo(NtBuAr)][BArF ] complexes has been accomplished by proton-coupled electron transfer. The 2,4,6-tri-tert-butylphenoxyl radical was used as an oxidant and the non-classical ammine complex [( Tpy)(PPh Me) Mo(NH )][BArF ] as the reductant. The N-H bond dissociation free energy (BDFE) of the amido N-H bond formed and cleaved in the sequence was experimentally bracketed between 45.

Ammonia Activation, H Evolution and Nitride Formation from a Molybdenum Complex with a Chemically and Redox Noninnocent Ligand.

Treatment of the bis(imino)pyridine molybdenum η-benzene complex (PDI)Mo(η-CH) (PDI, 2,6-(2,6-iPrCHN═CMe)CHN) with NH resulted in coordination induced haptotropic rearrangement of the arene to form (PDI)Mo(NH)(η-CH). Analogous η-ethylene and η-cyclohexene complexes were also synthesized, and the latter was crystallographically characterized. All three compounds undergo loss of the η-coordinated ligand followed by N-H bond activation, bis(imino)pyridine modification, and H loss.

Cobalt-Catalyzed 1,1-Diboration of Terminal Alkynes: Scope, Mechanism, and Synthetic Applications.

A cobalt-catalyzed method for the 1,1-diboration of terminal alkynes with bis(pinacolato)diboron (BPin) is described. The reaction proceeds efficiently at 23 °C with excellent 1,1-selectivity and broad functional group tolerance. With the unsymmetrical diboron reagent PinB-BDan (Dan = naphthalene-1,8-diaminato), stereoselective 1,1-diboration provided products with two boron substituents that exhibit differential reactivity.

C(sp)-H Borylation of Fluorinated Arenes Using an Air-Stable Cobalt Precatalyst: Electronically Enhanced Site Selectivity Enables Synthetic Opportunities.

Cobalt catalysts with electronically enhanced site selectivity have been developed, as evidenced by the high ortho-to-fluorine selectivity observed in the C(sp)-H borylation of fluorinated arenes. Both the air-sensitive cobalt(III) dihydride boryl 4-Me-(PNP)Co(H)BPin (1) and the air-stable cobalt(II) bis(pivalate) 4-Me-(PNP)Co(OCBu) (2) compounds were effective and exhibited broad functional group tolerance across a wide range of fluoroarenes containing electronically diverse functional groups, regardless of the substitution pattern on the arene. The electronically enhanced ortho-to-fluorine selectivity observed with the cobalt catalysts was maintained in the presence of a benzylic dimethylamine and hydrosilanes, overriding the established directing-group effects observed with precious-metal catalysts.

Insight into Transmetalation Enables Cobalt-Catalyzed Suzuki-Miyaura Cross Coupling.

Among the fundamental transformations that comprise a catalytic cycle for cross coupling, transmetalation from the nucleophile to the metal catalyst is perhaps the least understood. Optimizing this elementary step has enabled the first example of a cobalt-catalyzed Suzuki-Miyaura cross coupling between aryl triflate electrophiles and heteroaryl boron nucleophiles. Key to this discovery was the preparation and characterization of a new class of tetrahedral, high-spin bis(phosphino)pyridine cobalt(I) alkoxide and aryloxide complexes, (PNP)CoOR, and optimizing their reactivity with 2-benzofuranylBPin (Pin = pinacolate).

Coordination-induced weakening of ammonia, water, and hydrazine X-H bonds in a molybdenum complex.

Although scores of transition metal complexes incorporating ammonia or water ligands have been characterized over the past century, little is known about how coordination influences the strength of the nitrogen-hydrogen and oxygen-hydrogen bonds. Here we report the synthesis of a molybdenum ammonia complex supported by terpyridine and phosphine ligands that lowers the nitrogen-hydrogen bond dissociation free energy from 99.5 (gas phase) to an experimentally measured value of 45.

Thermodynamics of N-H bond formation in bis(phosphine) molybdenum(ii) diazenides and the influence of the trans ligand.

A series of bis(phosphine) molybdenum(ii) diazenides [(dppe)Mo(NNCy)(I)], [(dppe)(CHCN)Mo(NNCy)][BArF] and [(dppe))(3,5-(CF)CHCN)Mo(NNCy)][BArF] (dppe = 1,2-bis(diphenylphosphino)ethane; Cy = cyclohexyl; ArF = (3,5-(CF)CH)) were synthesized and structurally characterized. Treatment of the diazenido complexes with a stoichiometric amount of [H(OEt)][BArF] afforded the corresponding molybdenum(iv) hydrazido species [(dppe)Mo(NNHCy)(I)][BArF], [(dppe)(CHCN)Mo(NNHCy)][BArF] and [(dppe)(3,5-(CF)CHCN)Mo(NNHCy)][BArF], enabling the study of N-H bond dissociation free energies (BDFEs) in the classical Chatt-type bis(phosphine) diazenide platform as a function of ligand (L) trans to the nitrogenous fragment. Deprotonation and electrochemical experiments established that the trans nitrile 3,5-(CF)CHCN afforded the least reducing molybdenum(iv) hydrazido complex in the series ( = -1.

Expanding Boundaries: N2 Cleavage and Functionalization beyond Early Transition Metals.

Early transition metals are well known to catalyze the cleavage and functionalization of N2 . In this Highlight, recent work showing that a rhenium catalyst is also capable of carrying out this difficult task is summarized, and a synthetic cycle for the stoichiometric incorporation of atmospheric N2 into acetonitrile is presented.

Terpyridine Molybdenum Dinitrogen Chemistry: Synthesis of Dinitrogen Complexes That Vary by Five Oxidation States.

A bimetallic molybdenum complex bridged by an activated dinitrogen ligand and supported by phosphine and terpyridine ligands, [{((Ph)Tpy)(PPh2Me)2Mo}2(μ2-N2)][BArF(24)]2 [(Ph)Tpy = 4'-Ph-2,2',6',2″-terpyridine; ArF(24) = (C6H3-3,5-(CF3)2)4], was synthesized and structurally characterized, and its electronic structure was determined using a combination of experimental and density functional theory computational methods. Each molybdenum atom is best described as molybdenum(II) bridged by a modestly activated [N2](2-) ligand. The cyclic voltammogram of [{((Ph)Tpy)(PPh2Me)2Mo}2(μ2-N2)](2+) displays two reversible reductive and two reversible oxidative features, prompting the preparation and characterization of a series of molybdenum dinitrogen compounds spanning five oxidation states ([{((Ph)Tpy)(PPh2Me)2Mo}2(μ2-N2)][BArF(24)]n, where n = 4, 3, 2, 1, 0).

Ruthenium(II) complexes bearing a naphthalimide fragment: a modular dye platform for the dye-sensitized solar cell.

Cycloruthenated complexes of the type [Ru(II)(N^N)2(C^N)](+) (N^N = substituted 2,2'-bipyridine; C^N = substituted 3-(2'-pyridyl)-1,8-naphthalimide ligand) are shown to generate high power conversion efficiencies (PCEs) in the dye-sensitized solar cell (DSSC). It is shown that substitution of the pyridine ring of the C^N ligand with conjugated groups can enhance molar absorption extinction coefficients, while the electron density imparted on the metal center is alleviated by the 1,8-naphthalimide fragment. This latter feature maintains a Ru(III)/Ru(II) redox couple more positive than 0.