Yangjian Quan

Bio: Yangjian Quan is an academic researcher from The Chinese University of Hong Kong. The author has contributed to research in topics: Carborane & Regioselectivity. The author has an hindex of 22, co-authored 39 publications receiving 1383 citations. Previous affiliations of Yangjian Quan include Nanjing University & University of Chicago.

Iridium catalyzed regioselective cage boron alkenylation of o-carboranes via direct cage B-H activation.

Abstract: Iridium catalyzed alkyne hydroboration with o-carborane cage B–H has been achieved, leading to the formation of a series of 4-B-alkenylated-o-carborane derivatives in high yields with excellent regioselectivity via direct B–H bond activation. In this reaction the carboxy group is used as a traceless directing group, which is removed during a one-pot process. After the confirmation of a key intermediate, a possible mechanism is proposed, involving a tandem sequence of Ir-mediated B–H activation, alkyne insertion, protonation, and decarboxylation.

Controlled functionalization of o-carborane via transition metal catalyzed B–H activation

Abstract: Carboranes, a class of carbon-boron molecular clusters, are often viewed as three-dimensional analogues of benzene. They are finding increasing applications as useful functional building blocks in materials science, medicine, organometallic/coordination chemistry and more. Thus, functionalization of carboranes has received considerable attention. In comparison with the weakly acidic cage C-H bonds that can be readily functionalized, selective cage B-H functionalization among ten chemically similar BH vertices in o-carboranes is very challenging. Only in the recent few years, considerable progress has been made in transition metal catalyzed vertex-specific BH functionalization. This review summarizes recent advances in this research area.

Transition Metal Catalyzed Direct Amination of the Cage B(4)-H Bond in o-Carboranes: Synthesis of Tertiary, Secondary, and Primary o-Carboranyl Amines.

Abstract: Transition metal catalyzed regioselective amination of the cage B(4)–H bond in o-carboranes has been achieved for the first time using O-benzoyl hydroxylamines or organic azides as the amination reagents, leading to the preparation of a series of tertiary and secondary carboranyl amines. Both amination reactions proceeded under mild conditions without the addition of any external oxidants. Hydrogenolysis of the resultant product 4-N(CH2Ph)2-o-carborane afforded the primary carboranyl amine, 4-amino-o-carborane, in quantitative yield.

Transition Metal Catalyzed Selective Cage B‐H Functionalization of o‐Carboranes

Abstract: Carboranes are a class of carbon-boron molecular clusters with unusual thermal and chemical stabilities. They have been proved as very useful building blocks in supramolecular design, optoelectronics, nanomaterials, boron neutron capture therapy agents and organometallic/coordination chemistry. Thus, the functionalization of o-carboranes has received growing interests. Over the past decades, most of the works in this area have been focused on cage carbon functionalization as the weakly acidic cage C-H proton can be readily deprotonated by strong bases. In sharp contrast, selective cage B-H activation/functionalization among chemically very similar ten B-H vertices is very challenging. Considering the differences in electron density of ten cage B-H bonds in o-carborane and the nature of transition metal complexes, we have tackled this selectivity issue by means of organometallic chemistry. Our strategy is as follows: using electron-rich transition metal catalysts for the functionalization of the most electron-deficient B(3,6)-H vertices (bonded to both cage CH vertices); using electron-deficient transition-metal catalysts for the functionalization of relatively electron-rich B(8,9,10,12)-H vertices (with no bonding to both cage CH vertices); and using the combination of directing groups and electrophilic transition metal catalysts for the functionalization of B(4,5,7,11)-H vertices (bonded to only one cage CH vertex). Successful applications of such a strategy result in the preparation of a large variety of cage B-functionalized carboranes in a regioselective and catalytic manner, which are inaccessible by other means. It is believed that as this field progresses, other cage B-functionalized carboranes are expected to be synthesized, and the results detailed in this concept article will further these efforts.

Palladium-Catalyzed Regioselective Diarylation of o-Carboranes By Direct Cage B-H Activation.

Abstract: Palladium-catalyzed intermolecular coupling of o-carborane with aromatics by direct cage B-H bond activation has been achieved, leading to the synthesis of a series of cage B(4,5)-diarylated-o-carboranes in high yields with excellent regioselectivity. Traceless directing group -COOH plays a crucial role for site- and di-selectivity of such intermolecular coupling reaction. A Pd(II)-Pd(IV)-Pd(II) catalytic cycle is proposed to be responsible for the stepwise arylation.

Metal-Organic Framework-Based Catalysts with Single Metal Sites.

Abstract: Metal-organic frameworks (MOFs) are a class of distinctive porous crystalline materials constructed by metal ions/clusters and organic linkers. Owing to their structural diversity, functional adjustability, and high surface area, different types of MOF-based single metal sites are well exploited, including coordinately unsaturated metal sites from metal nodes and metallolinkers, as well as active metal species immobilized to MOFs. Furthermore, controllable thermal transformation of MOFs can upgrade them to nanomaterials functionalized with active single-atom catalysts (SACs). These unique features of MOFs and their derivatives enable them to serve as a highly versatile platform for catalysis, which has actually been becoming a rapidly developing interdisciplinary research area. In this review, we overview the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis. We also compare the results and summarize the major insights gained from the works in this review, providing the challenges and prospects in this emerging field.

Carboxylic Acids as Traceless Directing Groups for the Rhodium(III)‐Catalyzed Decarboxylative CH Arylation of Thiophenes

Abstract: A rhodium(III)-catalyzed carboxylic acid directed decarboxylative CH/CH cross-coupling of carboxylic acids with thiophenes has been developed. With a slight adjustment of the reaction conditions based on the nature of the substrates, aryl carboxylic acids with a variety of substituents could serve as suitable coupling partners, and a broad variety of functional groups were tolerated. This method provides straightforward access to biaryl scaffolds with diverse substitution patterns, many of which have conventionally been synthesized through lengthy synthetic sequences. An illustrative example is the one-step gram-scale synthesis of a biologically active 3,5-substituted 2-arylthiophene by way of the current method.

Visible light photocatalysis in the late-stage functionalization of pharmaceutically relevant compounds.

Abstract: The late stage functionalization (LSF) of complex biorelevant compounds is a powerful tool to speed up the identification of structure-activity relationships (SARs) and to optimize ADME profiles. To this end, visible-light photocatalysis offers unique opportunities to achieve smooth and clean functionalization of drugs by unlocking site-specific reactivities under generally mild reaction conditions. This review offers a critical assessment of current literature, pointing out the recent developments in the field while emphasizing the expected future progress and potential applications. Along with paragraphs discussing the visible-light photocatalytic synthetic protocols so far available for LSF of drugs and drug candidates, useful and readily accessible synoptic tables of such transformations, divided by functional groups, will be provided, thus enabling a useful, fast, and easy reference to them.

Iridium catalyzed regioselective cage boron alkenylation of o-carboranes via direct cage B-H activation.

Abstract: Iridium catalyzed alkyne hydroboration with o-carborane cage B–H has been achieved, leading to the formation of a series of 4-B-alkenylated-o-carborane derivatives in high yields with excellent regioselectivity via direct B–H bond activation. In this reaction the carboxy group is used as a traceless directing group, which is removed during a one-pot process. After the confirmation of a key intermediate, a possible mechanism is proposed, involving a tandem sequence of Ir-mediated B–H activation, alkyne insertion, protonation, and decarboxylation.