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Potential exists for construction time savings through replacement of cast-in-place substructure columns, piers, or both, with prefabricated bridge elements and systems. Cast-in-place substructure construction requires forming, placing steel, and pouring concrete at the construction site. Using prefabricated elements would decrease the extent of work required at the site and potentially reduce concrete curing time. This research furthers the effort to use ultra-high-performance concrete (UHPC) as a joining material for prefabricated bridge substructure elements. UHPC has a high early strength, requires less development or splice length than conventional concrete, and has been used previously for accelerated construction projects, such as bridge deck replacement with precast units. UHPC also has a discontinuous pore structure that reduces liquid ingress, significantly enhancing durability compared to conventional concrete. Although UHPC has been researched extensively, previous research for reinforcing bar splice and development lengths has focused on #9 and smaller diameter bars. Typically, larger diameter bars are used for substructures. This research determined the required splice lengths for large diameter steel deformed reinforcing bars embedded in UHPC based on 127 individual tests. Three primary variables were included in the testing matrix: bar size, bar spacing, and concrete cover. To achieve at least 75 kips per square inch (ksi) (517 MPa) reinforcing bar stress in UHPC with an early age strength of 14 ksi (97 MPa), the required embedment length ranges from 8 to 13 times the bar diameter and the corresponding splice length varies from 6 to 11 times the bar diameter, depending on the bar size and concrete cover.

The Suzuki–Miyaura cross-coupling of amides by selective N–C acyl bond cleavage represents a powerful tool for constructing biaryl ketones from historically inert amide bonds. These amide bond activation reactions hinge upon efficient oxidative addition of the N–C acyl bond to Pd(0). However, in contrast to the well-researched activation of aryl halides by C(sp2)–X oxidative addition, very few studies on the mechanism of C(acyl)–N bond oxidative addition and catalyst effect have been reported. Herein, we report a study on [Pd(NHC)(sulfide)Cl2] catalysts in amide N–C bond activation. These readily prepared, well-defined, air- and moisture-stable Pd(II)–NHC catalysts feature SMe2(DMS = dimethylsulfide) or S(CH2CH2)2(THT = tetrahydrothiophene) as ancillary ligands. The reaction development, kinetic studies, and reaction scope are presented. Extensive DFT studies were conducted to gain insight into the mechanism of C(acyl)–N bond oxidative addition and catalyst activation. We expect that [Pd(NHC)(sulfide)Cl2] precatalysts featuring sulfides as well-defined, readily accessible ancillary ligands will find application in C(acyl)–X bond activation in organic synthesis and catalysis.

The development of efficient and operationally simple synthetic routes to dinuclear gold(i)-amido complexes bearing aromatic/aliphatic-bridges are reported. This family of complexes was prepared utilizing environmentally friendly and sustainable reagents under mild conditions, resulting in 68–92% yields of the targeted compounds. These novel dinuclear gold(i)-amido complexes were structurally and spectroscopically characterized. Their photophysical properties were also studied. This series of gold complexes are phosphorescent with lifetimes in the hundreds of microseconds range. They exhibit high catalytic activity as photosensitizers in intramolecular cycloaddition and cyclization reactions at catalyst loadings ranging from 0.5 to 2 mol%.

We report a combined experimental and mechanistic study on the Buchwald–Hartwig amination and C–S/S–H metathesis of aryl sulfides by selective activation of C–S bonds mediated by well-defined, air- and moisture-stable Pd(II)–NHC precatalysts, [Pd(NHC)(μ-Cl)Cl]2. This class of Pd(II)–NHC precatalysts displays excellent activity in the cross coupling of aryl sulfides. Most crucially, we unravel the unified mechanism for activation of C–S bonds in the C–N cross-coupling and C–S metathesis manifolds, where the inert C–S bond serves as a precursor to valuable amine or thioether products.

Continuous flow reactors have earned their place as an important technology in organic synthesis, receiving increased interest in the past decade. The favorable heat and mass transfer capabilities, combined with the ease of scale-up, have not only made it a safer option in many cases, but often the only option when dealing with highly reactive, short-lived intermediates. In this review, an overview is given of the most recent advances made in the flow synthesis of organometallic compounds. This includes both main group and transition metal applications.

A simple and efficient method for the oxidative coupling of terminal alkynes is reported for the first time, making use of imidazol(in)ium aurates as pre-catalysts. This approach displays high functional group tolerance and leads to a broad range of 1,3-diyne compounds in moderate to excellent yields using low catalyst loading and is performed in air under mild and sustainable conditions.

The cross-coupling of aryl esters has emerged as a powerful platform for the functionalization of otherwise inert acyl C–O bonds in chemical synthesis and catalysis. Herein, we report a combined experimental and computational study on the acyl Suzuki–Miyaura cross-coupling of aryl esters mediated by well-defined, air- and moisture-stable Pd(ii)–NHC precatalysts [Pd(NHC)(μ-Cl)Cl]2. We present a comprehensive evaluation of [Pd(NHC)(μ-Cl)Cl]2precatalysts and compare them with the present state-of-the-art [(Pd(NHC)allyl] precatalysts bearing allyl-type throw-away ligands. Most importantly, the study reveals [Pd(NHC)(μ-Cl)Cl]2as the most reactive precatalysts discovered to date in this reactivity manifold. The unique synthetic utility of this unconventional O–C(O) cross-coupling is highlighted in the late-stage functionalization of pharmaceuticals and sequential chemoselective cross-coupling, providing access to valuable ketone products by a catalytic mechanism involving Pd insertion into the aryl ester bond. Furthermore, we present a comprehensive study of the catalytic cycle by DFT methods. Considering the clear advantages of [Pd(NHC)(μ-Cl)Cl]2precatalysts on several levels, including facile one-pot synthesis, superior atom-economic profile to all other Pd(ii)–NHC catalysts, and versatile reactivity, these should be considered as the ‘first-choice’ catalysts for all routine applications in ester O–C(O) bond activation.

N-heterocyclic carbenes (NHCs) are a widely used class of ligands that have enabled an exciting variety of organometallic chemistry and catalysis. As researchers design and customize these ligands for specific applications, various design concepts have emerged. This review covers several of these design concepts and their impact on and promise for organometallic chemistry and catalysis. These concepts are bulky ligands that remain flexible for substrate binding and reactivity, ring-expanded NHCs with different steric and electronic properties, NHCs appended to supramolecular assemblies that control the microenvironment around the metal center; and NHCs with pendant labile functional groups.

Transition metal complexes bearing N-heterocyclic carbene ligands (NHCs) have gained a place of crucial importance in numerous areas of research such as medicinal chemistry, material sciences, and homogeneous/heterogeneous catalysis. In the present review, an updated overview of the main synthetic routes used for the preparation of this broad class of compounds along with their main applications are reported. Particular attention will be paid to the synthesis of late transition metal–NHC complexes using weak bases, eco-friendly solvents, and mild operating conditions. This simple synthetic approach, also known as the ‘weak base route’, represents a recent development with yet unrealized potential.

The weak base method in continuous flow is currently one of the most sustainable and attractive approaches towards the synthesis of transition metal N‐heterocyclic carbene (NHC) complexes. Herein we broaden the scope of this method by using it to produce [M(IPr)(OC(H)(CF3)2)] complexes, including copper, silver, and gold. These compounds bear the alkoxide ligand within the coordination sphere of the catalysts, which can open up new ways to benefit from the unique properties offered by HFIP (1,1,1,3,3,3‐hexafluoroisopropanol) in catalysis, while minimizing the needed amount. The weak base route in continuous flow is described for [M(IPr)(OC(H)(CF3)2)] (M=Cu, Ag and Au) complexes under unprecedently fast and mild conditions. These complexes which are remarkably stable could become versatile air‐stable synthons that could be used in a wide range of catalytic reactions.

The Pd–NHC-catalyzed acyl-type Buchwald–Hartwig cross-coupling of amides by N–C(O) cleavage (transamidation) provides a valuable alternative to the classical methods for amide synthesis. Herein, we report a combined experimental and computational study of the Buchwald–Hartwig cross-coupling of amides using well-defined, air- and moisture-stable [Pd(NHC)(allyl)Cl] precatalysts. Most crucially, we present a comprehensive evaluation of a series of distinct Pd(ii)–NHC precatalysts featuring different NHC scaffolds and throw-away ligands for the synthesis of functionalized amides that are not compatible with stoichiometric transition-metal-free transamidation methods. Furthermore, we present evaluation of the catalytic cycle by DFT methods for a series of different Pd(ii)–NHC precatalysts. The viability of accessing NHC-supported acyl-palladium(ii) amido complexes will have implications for the design and development of cross-coupling methods involving stable amide electrophiles.

A general class of well-defined, air-stable, and readily available Pd(II)-NHC precatalysts (NHC = N-heterocyclic carbene) for Suzuki and Buchwald–Hartwig cross-coupling of amides (transamidation) and esters by selective N–C/O–C cleavage is reported. Since these precatalysts are highly active and the easiest to synthesize, the study clearly suggests that [Pd(NHC)(acac)Cl] should be routinely included during the development of new cross-coupling methods. An assay for in situscreening of NHC salts in this cross-coupling manifold is presented.

To support and promote the deployment of innovative technologies in infrastructure, it is fundamental to quantify their implications in terms of both economic and environmental impacts. Glass Fiber-Reinforced Polymer (GFRP) bars and Carbon Fiber-Reinforced Polymer (CFRP) strands are validated corrosion-resistant solutions for Reinforced Concrete (RC) and Prestressed Concrete (PC) structures. Studies on the performance of Fiber-Reinforced Polymer (FRP) reinforcement in seawater and salt-contaminated concrete have been conducted and show that the technology is a viable solution. Nevertheless, the economic and environmental implications of FRP-RC/PC deployment have not been fully investigated. This article deals with the Life-Cycle Cost (LCC) and Life-Cycle Assessment (LCA) analyses of an FRP-RC/PC bridge in Florida. The bridge is designed to be entirely reinforced with FRP bars and strands and does not include any Carbon Steel (CS) reinforcement. Furthermore, the deployment of seawater concrete in some of the elements of the bridge is considered. LCC and LCA analyses are performed at the design stage. Data regarding equipment, labor rates, consumables, fuel consumption, and disposal were collected during the construction phase, and the analysis was refined accordingly. The FRP-RC/PC bridge design is compared with a traditional CS-RC/PC alternative. Salient differences are discussed to determine the least-impactful solution from both an economic and environmental perspective.

Palladium-catalyzed cross-coupling reactions owing to their high specificity and superb chemoselectivity represent a powerful tool for the rapid construction of C–C and C–X bonds across various areas of chemical research, including pharmaceutical development, polymer and agrochemical industries, bioactive natural products, and advanced functional materials, rendering them indispensable for modern synthetic chemists. The major driving force for the advances in this critical field is the design of increasingly more reactive and more selective ligands and precatalysts that aim not only to address challenging cross-coupling processes but also to achieve optimal reactivity, selectivity, and functional group compatibility under mild, user-friendly, operationally simple, and broadly applicable conditions. In this context, Pd(II)–N-heterocyclic carbene complexes (NHC = N-heterocyclic carbene) have garnered prevalent attention among practitioners of organic synthesis due to their unique electronic and steric characteristics that are unmatched among other ligands. In particular, the superior σ-donating ability of NHC ligands in conjunction with conformational flexibility as well as the ease of steric and electronic modification and high stability to air and moisture enable highly effective fundamental elementary steps in catalytic cycles and facile formation of well-defined complexes.

Eight new dinuclear gold(I) complexes, [Au2(L)X2] (1–8), were synthesized using a straightforward synthetic procedure under very mild conditions. The complexes have been characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray structure analysis. Their catalytic activity was investigated in the carboxylative cyclization of propargylamine (PPA). A superior performance in comparison to [Au(IPr)Cl] (9) was obtained for complexes 1and 2having an eight-methylene bridge connecting two NHCs with an arene bearing an isopropyl substituent for X = Cl, Br. This prompted more detailed kinetic and mechanistic studies by FTIR comparing dinuclear complex 2of X = Cl to complex 9. Fortuitously the FTIR studies allowed monitoring of the formation of the products carbamic acid (CA) and carbamate salt (CS), as well as a key cyclized intermediate first discovered by Ikariya. These data allow additional insight into the mechanism as well as the central role which may be played by Au(I) carbamate formation as a higher energy resting state present in the catalytic cycle. The crystal structures of four of the new complexes and a detailed computational study relevant to the role of carbamic acid (CA) and carbamates in the catalytic cycle are also reported.

In this study, we present for the first time the immobilization of phosphotungstic acid (H3PW12O40, HPW) into the nanocages of a dual amino-functionalized ionic liquid (DAIL)-modified MIL-101(Cr) framework under mild conditions. The obtained PW/DAIL/MIL-101(Cr) was evaluated as a catalyst in the oxidation of benzyl alcohol using TBHP in chloroform. In order to obtain insights into the role of the DAIL during catalysis, a DAIL-free catalyst (HPW/MIL-101(Cr)) was also prepared. Both catalysts were fully characterized using several techniques. In comparison with the HPW/MIL-101(Cr) material, PW/DAIL/MIL-101(Cr) showed an enhanced catalytic performance in the selective oxidation of benzyl alcohol. This was mainly attributed to the ability of the DAIL groups to form hydrogen bonds, thus enhancing the accessibility of TBHP. Furthermore, the immobilization of the DAIL groups onto MIL-101(Cr) resulted in increased thermal stability of the obtained PW/DAIL/MIL-101(Cr) which showed stability up to 400 °C. Moreover, the PW/DAIL/MIL-101(Cr) catalyst exhibited good recyclability and selectivity. The catalyst could be reused for at least five cycles with no significant leaching of the tungsten species or loss of crystallinity and activity.