Anionic N-Heterocyclic Carbenes Featuring Carboranes: Reactivity and Catalysis

Carbenes are neutral, divalent, six electron carbon species. Although initially perceived as reaction intermediates, pioneering work from Bertrand showed that they can be isolated in the laboratory. Further, Arduengo isolated N-Heterocyclic Carbenes (NHCs), a stable variety of persistent carbenes usually flanked by bulky aryl groups. These compounds have become popular as strongly coordinating ligands for transition metals producing some of the most active catalysts so far. Since then, there has been a growing interest in the development of NHCs for transition metal catalysis. Over the past few years, our lab has been developing NHCs featuring weakly coordinating Carborane anions. Due to the inherent charge on these molecules, the resulting NHCs are overall mono or dianionic depending on the number of carboranes in the molecule.To impart more robust nature for reactivity investigations, the dianionic 12-vertex closo carboranyl NHCs were hexahalogenated. The monoanionic Au(I) complex of this NHC is itself a weakly coordinating anion allowing us to pair it with a variety of main-group and organometallic cations. The synthetic utility of these ion-pairs was demonstrated by a tandem hydroamination of alkynes followed by the hydrosilylation of the imines using a Au(I)/N-methyl benzothiazolium system. The scope of these carboranyl NHCs was then expanded to the 10-vertex closo carborane where stable NHCs bearing this carborane were synthesized using novel synthetic methods. Perchlorination of this carbene, including the backbone bearing the imidazolylidene ring rendered an unprecedented water stable carbene. Moreover, we show the 10-vertex carboranyl NHC is a strong ligand through synthesis of the corresponding Cu(I) and Au(I) complexes. The dicarbollide ligand, derived from the o-carborane was then functionalized to produce the bis(dicarbollide)iron appended NHCs, the isolobal equivalents of ferrocene. Despite the long-established analogy with ferrocenes, these complexes were seen to behave in a promiscuous way. An unusual transmetalation reaction with other transition metals was discovered to produce the first examples of metallacarborane appended NHCs. Coordination of these NHCs with Cu(I) produced bimetallic complexes with a rare coordination environment. The promiscuous nature of the dicarbollide-NHC ligands was further illustrated by their diverse reactivity with a Pd(II) precursor

Recent Advancements in Evacuated Tube Solar Water Heaters: A Critical Review of the Integration of Phase Change Materials and Nanofluids with ETCs

Evacuated tube solar water heaters are gaining more attention in the present market scenario as compared to conventional collectors. Such collectors are versatile because no solar tracking is required and the operating temperature range is also broad. Comparatively, it is cost-effective and may attain higher thermal efficiency. However, like other collectors, continuous energy supply is sometimes hampered by the intermittent nature of solar radiation. This problem can be partially resolved by using phase change materials (PCM) in the evacuated tube solar collector (ETC). PCMs can store the energy during the sunshine hours, which can be released when solar energy is not available. In the literature, several studies are available pertaining to the use of PCMs in ETC-based solar water heaters. The literature indicates that the integration of PCMs with ETCs has several merits. Nevertheless, systematic, and comprehensive review papers dedicated to such integrated energy storage systems with ETC solar water heaters are not available. Hence, the objective of this work is to compile the relevant experimental, numerical, and theoretical works reported in the literature. The present paper broadly reviews the recent design modifications, PCM integration with different kinds of ETC water heaters, and their life cycle assessment. Furthermore, studies in the literature pertaining to the application of nanoparticles in ETC systems are also discussed, and finally, a roadmap for this energy storage system is provided

Infantile fetiform abdominal mass: Teratoma or fetus in fetu? A case report with insights into radiological diagnosis and surgical management

Fetus-in-fetu (FIF) is a rare congenital anomaly in which a malformed parasitic twin develops within the body of a live fetus or child. Abdominal teratoma, a type of germ cell tumor, can be a great imaging mimicker of FIF and vice-versa, as they both can present as a heterogeneous mass with calcifications and a fat component. Radiological differentiation of these 2 entities should be made because of the difference in surgical planning and treatment options. Features such as visualization of distinct bony vertebral elements and encysted cystic components are the specific features of Fetus in fetu [1]. In contrast, the presence of elevated serum markers can help diagnose teratoma. Here, we report a case of a 5-month-old girl presented with progressive distension of the upper abdomen for the last 2 months, noticed by her mother. Her initial imaging with abdominal X-ray and ultrasonography showed the presence of a large heterogenous solid-cystic mass in the upper abdomen with large elongated calcifications. A provisional diagnosis of teratoma vs FIF was considered. CECT abdomen showed clear identification of osseous structures of the axial and appendicular skeleton within a fat density mass, along with an encapsulated cystic component, strongly suggestive of FIF. Her serum tumor markers were within normal limits. The final diagnosis of FIF was confirmed on Laparotomy and postoperative specimens

Strongly Coordinating Ligands To Form Weakly Coordinating Yet Functional Organometallic Anions

Weakly coordinating anions (WCAs) are generally tailored to act as spectators with little or no function. Here we describe the implementation of strongly coordinating dianionic carboranyl N-heterocyclic carbenes (NHCs) to create organometallic -ate complexes of Au(I) that serve both as WCAs and functional catalysts. These organometallic WCAs can be utilized to form both heterobimetallic (Au(I)−/Ag(I)+; Au(I)−/Ir(I)+) and organometallic/main group ion pairs (Au(I)−/(CPh3+ or SiEt3+). Because parent unfunctionalized dianionic carboranyl NHC complex 3 is unstable in most solvents when paired with CPh3+, novel synthesis methodology was devised to create polyhalogenated carboranyl NHCs, which show superior stability toward electrophilic substitution and cyclometalation chemistry. Additionally, the WCAs containing polyhalogenated carboranyl NHCs are among the most active catalysts reported for the hydroamination of alkynes. This investigation has also produced the first examples of a low-coordinate Au(III) center with two cis accessible coordination sites and the first true dianionic carbene. These studies pave the way for the design of functional ion pairs that have the potential to participate in tandem or cooperative small-molecule activation and catalysis