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Reaction of the mononuclear nonheme complex [Fe(II)(CH(3)CN)(N3PyS)]BF(4) (1) with an HNO donor, Piloty’s acid (PhSO(2)NHOH, P.A.), at low temperature affords a high-spin (S = 2) Fe(II)-P.A. intermediate (2), characterized by (57)Fe Mössbauer and Fe K- edge X-ray absorption (XAS) spectroscopies, with interpretation of both supported by DFT calculations. The combined methods indicate that P.A. anion binds as the N-deprotonated tautomer (PhSO(2)NOH(−)) to [Fe(II)(N3PyS)](+), leading to 2. Complex 2 is the first spectroscopically characterized example, to our knowledge, of P.A. anion bound to a redox-active metal center. Warming of 2 above −60 °C yields the stable {FeNO}(7) complex [Fe(NO)(N3PyS)]BF(4) (4), as evidenced by (1)H NMR, ATR-IR, and Mössbauer spectroscopies. Isotope labeling experiments with (15)N-labeled P.A. confirm that the nitrosyl ligand in 4 derives from P.A. In contrast, addition of a second equivalent of a strong base leads to S-N cleavage and production of an {FeNO}(8) species, the deprotonated analog of an Fe-HNO complex. This work has implications for the targeted delivery of HNO/ NO(−)/NO‧ to nonheme Fe centers in biological and synthetic applications, and suggests a new role for nonheme Fe(II) complexes in the assisted degradation of HNO donor molecules.

A nonheme {FeNO}6 complex, [Fe(NO)(N3PyS)]2+ , was synthesized by reversible, one-electron oxidation of an {FeNO}7 analogue. This complex completes the first known series of sulfur-ligated {FeNO}6-8 complexes. All three {FeNO}6-8 complexes are readily interconverted by one-electron oxidation/reduction. A comparison of spectroscopic data (UV/Vis, NMR, IR, Mossbauer, X-ray absorption) provides a complete picture of the electronic and structural changes that occur upon {FeNO}6 -{FeNO}8 interconversion. Dissociation of NO from the new {FeNO}6 complex is shown to be controlled by solvent, temperature, and photolysis, which is rare for a sulfur-ligated {FeNO}6 species.

Development of photoelectrochemical(PEC) reduction of CO2 has helped in harnessing its potential as a versatile feedstock for generation of alternative fuels. In this regard, emergence of hybrid semiconductor based photocathodes in conjunction with metal cocatalysts, metal fabrications and other photoanodes are noteworthy owing to their efficient catalytic conversion and appreciable selectivity. Since its discovery in 1978, a series of reports have been presented that helped in production of CO, HCOOH, CH3OH as well as CH4 by CO2 reduction using hybrid semiconductor based systems. This review aims to highlight some of these major developments from the past few years with the aim of fostering further scientific perception about the true potential of this research area and encouraging future research investigations.

A palladium(II)-catalyzed protocol for the highly regioselective remote γ-C–H arylation of aliphatic carboxylic acid has been disclosed. The 8-aminoquinoline moiety as an intramolecular bidentate chelator was found to be suitable for this γ-C–H arylation. Various aryl iodides successfully produced the regioselectively mono-arylated products with negligible diarylation. Functional group tolerance and easy-to-handle reaction conditions make this method attractive.

Heterocyclic compounds are commonly found in the core structures of several pharmaceuticals, natural products, and agrochemicals, thus spurring intensive research for conducting their synthesis in a mild and simpler way. Over the years, a host of different strategies has been introduced in an effort to synthesize these heterocyles. In this context, significant attention has been gained by methodologies that ensure both step as well as atom efficiency. Synthesis of heterocyclic moieties via multiple C-H activations was found to fulfill these expectations besides guaranteeing the use of starting materials that are easily procurable. This review is focused on the current development in the field of benzofuran and indole synthesis using multiple C-H functionalization strategies.

To date, cleavage of the C-N bond in aromatic amides has been achieved in molecules with a distorted constitutional framework around the nitrogen atom. In this report, a nickel-catalyzed reduction of planar amides to the corresponding lower hydrocarbon homologue has been reported. This involves a one-pot reductive cleavage of the C-N bond followed by a tandem C-CO bond break in the presence of a hydride source. Substrate scope circumscribes deamidation examples which proceed via oxidative addition of nickel in the amide bonds of nontwisted amides. Mechanistic studies involving isolation and characterization of involved intermediates via different spectroscopic techniques reveal a deeper introspection into the plausible catalytic cycle for the methodology.

The halogenation of the C-H bond by metal-oxo-peroxo species and the decarbonylation of aldehydes by metal-peroxo species are performed routinely in biological systems. However, metal-mediated decarbonylative halogenation is unknown in nature. In this work, we have shown that widely available V2O5 and VO(acac)(2) (acac=acetylacetonate) can catalyze decarbonylative halogenation through the generation of an inter-mediate vanadium-oxo-peroxo species, which was characterized by using V-51 NMR, UV/Vis, and resonance Raman spectroscopy. Further detection of formic acid from the reaction mixture confirmed the biomimetic aspects of decarbonylative halogenation. A detailed experimental and DFT study indicated a concerted mechanism for this decarbonylative halogenation performed under simple and mild reaction conditions.

Owing to the synthetic importance of branched olefinated products, we report palladium catalyzed formation of branched olefins facilitated by a C-H activation based protocol. This involves selective insertion of olefins and subsequent decarboxylation using a completely unbiased benzene ring as the starting precursor. The significance of the protocol has been further highlighted by exhibition of functionality tolerance along with a late-stage modification of the branched olefinated products leading to the formation of other functionalized molecules.

Application of transition metal-catalyzed C H activation reactions to natural product synthesis is an emerging and exciting area of research that not only obviates the need for prefunctionalization of the substrates, but also bypasses multistep sequences providing opportunities for designing new retrosynthetic paradigms. The key challenges associated with this field are the compatibility and selectivity issues with polyfunctionalized substrates. Palladium-catalyzed directed functionalization of C H bonds is gaining a lot of attention as a new synthetic strategy maximizing the atom- and step-economy, and has found application in the planned synthesis of many natural products and biologically active compounds. In this chapter, we aim to highlight the recent applications of palladium-catalysis for the synthesis of complex molecular frameworks wherein C H activation was employed as a key step.

The growing importance of functionalities located at suitable positions within an organic moiety bestows it with specific properties. This renders value-added properties to these molecules, thereby augmenting their utilitarian characteristics. In regard to this, transformation of sp3 C H bonds becomes quite challenging owing to their low reactivity and relative inertness compared to their sp2 and sp congeners. Complexity is further amplified in the attempts for functionalization at remote positions with respect to the pre-installed functional groups. This chapter therefore highlights some recent advances made in the field of aliphatic distal C H functionalization which has been made possible through the employment of an assortment of strategies.

The applicability of C–H functionalization to medicinally important 2-pyridyl-based N-heterocycles suffers from severe challenges owing to the high Lewis basicity of the N-atom. This arrests catalytic activity and yields undesirable positional selectivity due to preferential chelate formation. In this regard, we report a novel palladium(II)-catalyzed arylation strategy on multiple-N-containing pyridazines by over-riding the functionalization due to a chelated palladacycle. We report a regioselective mono-arylation at the 8-position of diphenyl azolopyridazines without any ortho-C–H activation on the proximal phenyl groups. This methodology presents a broad arylation scope with uncompromised yield and positional selectivity, including the heteroarylation of N-heterocycles, which is an unprecedented feat for these types of molecules.

Regioselective functionalization of aromatic arenes has created a rapid insurgence in the modern era of organic chemistry. While the last few years have witnessed significant developments on site-selective ortho- and meta-C–H transformations, there existed very few reports on para-C–H functionalization. Recent advancements on template assisted protocols in para-C–H activation has emerged as a popular and convenient feat in this area. This review highlights the various protocols developed over the years for selective installation of suitable functional groups at the para-position of arenes thereby transforming them into value-added organic cores.

The directing group assisted site selective C–H functionalization approach is having a continuous impact in the field of natural product synthesis, drug discovery and material sciences. While ortho-selective C–H functionalization has been studied extensively, meta-selective C–H functionalization has been less explored. Recent studies have highlighted the efficacy of palladium as a catalyst in activating the meta-C–H bond of arenes. Notably, the introduction of a novel palladium catalysed directing template based approach to activate the remote meta-position has created a revolutionary impact towards seeking a solution to this long standing challenge. In this review we summarize recent advances in palladium catalysed meta-C–H functionalization that have helped in creating a new outlook towards modern organic synthesis.

Various practical methods for the selective C-H functionalization of the ortho and recently also of the meta position of an arene have already been developed. Following our recent development of the directing-group-assisted para C-H functionalization of toluene derivatives, we herein report the first remote para C-H functionalization of phenol derivatives by using a recyclable silicon-containing biphenyl-based template. The effectiveness of this strategy was illustrated with different synthetic elaborations and by the synthesis of various phenol-based natural products.