Preparation of Aryl and Heteroaryl Indium(III) Reagents by the Direct Insertion of Indium in the Presence of LiCl

One-Step Transformation of Aryl Diazonium Salts into Aryl Indium(III) Reagents

A method for the conversion of diazonium salts into intrinsically nucleophilic aryl indium reagents is described. The reaction is performed using indium(I) bromide with the C-In bond being formed by the interaction of aryl radicals with the indium salt. The obtained aryl indium(III) reagents work well in the Liebeskind-Srogl cross-coupling with thioesters, affording a wide variety of aryl ketones. This two-step transformation is a general method for the acylation of diazonium salts.

Trimethylsilyl Chloride Aids in Solubilization of Oxidative Addition Intermediates from Zinc Metal

Trimethylsilyl chloride (TMSCl) is commonly used to "activate" metal(0) powders toward oxidative addition of organohalides, but knowledge of its mechanism remains limited by the inability to characterize chemical intermediates under reaction conditions. Here, fluorescence lifetime imaging microscopy (FLIM) overcomes these prior limitations and shows that TMSCl aids in solubilization of the organozinc intermediate from zinc(0) metal after oxidative addition, a previously unknown mechanistic role. This mechanistic role is in contrast to previously known roles for TMSCl before the oxidative addition step. To achieve this understanding, FLIM, a tool traditionally used in biology, is developed to characterize intermediates during a chemical reaction-thus revealing mechanistic steps that are unobservable without fluorescence lifetime data. These findings impact organometallic reagent synthesis and catalysis by providing a previously uncharacterized mechanistic role for a widely used activating agent, an understanding of which is suitable for revising activation models and for developing strategies to activate currently unreactive metals.

Oxidative Addition of Aryl Electrophiles into a Red-Light-Active Bismuthinidene

The oxidative addition of aryl electrophiles is a fundamental organometallic reaction widely applied in the field of transition metal chemistry and catalysis. However, the analogous version based on main group elements still remains largely underexplored. Here, we report the ability of a well-defined organobismuth(I) complex to undergo formal oxidative addition with a wide range of aryl electrophiles. The process is facilitated by the reactivity of both the ground and excited states of N,C,N-bismuthinidenes upon absorption of low-energy red light.

Origins of Batch-to-Batch Variation: Organoindium Reagents from Indium Metal

Yields of organoindium reagents synthesized from indium metal were previously reported to be highly dependent on metal batch and supplier due to the presence or absence of anticaking agent. Here, single-particle fluorescence microscopy established that MgO, an additive in some batches nominally for anticaking, significantly increased the physisorption of small-molecule organics onto the surface of the resulting MgO-coated indium metal particles. An inert and relatively nonpolar boron dipyrromethene fluorophore with a hydrocarbon tail provided a sensitive probe for this surface physisorption. SEM images revealed markedly different surface properties of indium particles either with or without MgO, consistent with their different physisorption properties observed by fluorescence microscopy. We further documented incomplete commercial bottle labeling regarding the presence and composition of this anticaking agent, both within our laboratory and previously in the literature, which may complicate reproducibility between laboratories. Trimethylsilyl chloride pretreatment, a step employed in a subset of reported synthetic procedures, removed the anticaking agent and produced particles with similar physisorption properties as commercial batches of indium powder distributed without the anticaking agent. These data indicate the possibility of an additional substrate/catalyst physisorption mechanism by which the anticaking agent may be influencing synthetic procedures that generate organoindium reagents from indium metal, in addition to simple anticaking.

Palladium-catalyzed cross-coupling of (hetero)aryl or alkenyl sulfonates with aryl titanium as the multi-functional reagent

The first palladium-catalyzed cross-coupling reaction of aryl/heteroaryl and alkenyl mesylates and tosylates with aryl titanium as the multi-functional reagent is reported.

Indium-mediated difunctionalization of iodoalkyl-tethered unactivated alkenes via an intramolecular cyclization and an ensuing palladium-catalyzed cross-coupling reaction with aryl halides

A cobalt-catalyzed, indium-mediated difunctionalization of iodoalkyl-tethered unactivated alkenes for accessing five-membered cyclic compounds via a cyclization/cross-coupling sequence was developed.

Microscopy Reveals: Impact of Lithium Salts on Elementary Steps Predicts Organozinc Reagent Synthesis and Structure

Lithium chloride is known to promote the direct insertion of metallic zinc powder into organohalides in the practical synthesis of organozinc reagents, but the reason for its special ability is poorly understood. Pioneering a combined approach of single-metal-particle fluorescence microscopy with ¹H NMR spectroscopy, we herein show that the effectiveness of different lithium salts toward solubilizing intermediates on the surface of zinc metal establishes a previously unknown reactivity correlation that predicts the propensity of that salt to promote macroscale reagent synthesis and also predicts the solution structure of the ultimate organozinc reagent. A salt-free pathway is also identified. These observations of an organometallic surface intermediate, its elementary-step reactivity, and the impact of various synthetic conditions (salt, salt-free, temperature, stirring, and time) on its persistence, are uniquely available from the sensitivity and spatial localization ability of the microscopy technique. These studies unify previously disparate observations under a single unified mechanistic framework. This framework enables the rational prediction of salt effects on multiple steps in organozinc reagent synthesis and reactivity. This is an early example of single-particle microscopy characterization of elementary steps providing predictive power in reaction development by gaining a sensitive and selective spectral handle on an important intermediate, highlighting the role of this next generation of analytical tools in the development of synthetic chemistry.

Metallic salt-catalyzed direct indium insertion into alkyl iodides and their applications in cross-coupling reactions

An efficient method for the synthesis of alkyl indium reagents via an indium(iii) or lead(ii) halide-catalyzed direct insertion of indium into alkyl iodides is developed. NMR and ESI-MS analyses indicated the formation of a mixture of an alkyl indium dihalide (RInX₂) and a dialkyl indium halide (R₂InX).

Triorganoindium Reagents in Rh-Catalyzed C⁻H Activation/C⁻C Cross-Coupling Reactions of 2-Arylpyridines

The activation of C–H bonds through catalytic reactions using transition metals is an important challenge in organic chemistry in which the intermediates are related to those produced in the classical cross-coupling reactions. As part of our research program devoted to the development of metal-catalyzed reactions using indium organometallics, a protocol for the C–H activation and C–C coupling of 2-arylpyridines with triorganoindium reagents under Rh(I) catalysis is reported. Under the optimized conditions, we found that Me₃In and Ar₃In reagents reacted with 2-arylpyridines and related compounds in the presence of Rh(PPh₃)₃Cl, in PhCl/THF (9:1), at 120 °C for 48 h, to afford the ortho-coupling products in moderate to good yields. The nitrogen atom in the pyridine ring acts as a directing group to assist the functionalization at the ortho position of the aryl group forming a new C–C bond at this position.

Transition metal-catalyzed cross-coupling reactions using organoindium reagents

This review highlights the versatility and significance of transition metal-catalyzed cross-coupling reactions employing mild and unique organoindium reagents with exceptional functional group compatibility and sometimes remarkable chemo- and stereoselectivities.

Indium triflate-catalyzed stereoselective tandem intramolecular conjugate addition of secondary amines to α,β-bisenones

We report an indium triflate-catalyzed stereoselective intramolecular tandem conjugate addition of secondary amines to α,β-bisenones to afford a 1,2,3-trisubstituted six-membered ring bearing diketone substituents in good to excellent yields at room temperature.

The Barbier-Grignard-type arylation of aldehydes using unactivated aryl iodides in water

Carbon-carbon bond formation is the essence of organic synthesis. One of the most important methods for forming carbon-carbon bonds is the Barbier-Grignard-type reaction, which was discovered over a century ago. However, it is still highly desirable to further improve this process. In this article, we describe a Barbier-Grignard-type direct arylation of aldehydes by using unactivated iodides mediated by zinc and catalysed by rhodium in water. This method bypasses a number of challenges encountered by the conventional Barbier-Grignard reaction, such as strict exclusion of moisture and air, protection-deprotection of various acidic hydrogens in the substrates, and so forth. It thereby creates a safer, more convenient and more environmentally benign strategy to access the diarylmethanols and aryl alkyl alcohols, ubiquitous skeletons found in fine chemicals, biologically active molecules and pharmaceuticals. Importantly, the same reaction performed in an organic solvent proceeded sluggishly to give much inferior yields.