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This review highlights transborylation (controlled boron-boron exchange) and its applications as a turnover strategy in boron-catalysed methodologies. Catalytic applications of B –C, B –O, B –N, B –F, B –S, and B –Se transborylations are discussed in the context of transborylation-enabled catalysis, across a wide range of organic transformations including hydroboration, C–C bond formation, C–H borylation, chemoselective reduction, and asymmetric reduction. 1 Introduction 2 B –C Transborylation 3 B –O Transborylation 4 B –N Transborylation 5 B –F Transborylation 6 B –S Transborylation 7 Conclusion [ABSTRACT FROM AUTHOR]

Arene borylation reactions provide direct access to aryl organoboranes, including aryl boronic esters. Precious metals, namely Ir, Rh, Pt, remain the go-to for metal-catalysed borylation reactions, however, significant efforts have been expended in developing Earth-abundant metal alternatives. The iron-catalysed borylation of 2-aryl pyridine derivatives with 9-borabicyclo[3.3.1]nonane (H-B-9-BBN) offers unique reactivity by using only FeBr 3 as the catalyst, without added ligand(s). Mechanistic analysis of this borylation reaction revealed an alternative, hidden catalysis pathway whereby the iron salt acts not as a borylation catalyst, but as an initiator for the generation of a catalytically active haloborane, Br-B-9-BBN. The roles of iron salt, Br-B-9-BBN, and HBr in catalyst formation, the mode of catalytic turnover, and catalyst regeneration were all determined using single-turnover and catalytic studies. The borylation reaction was found to proceed by a catalytic electrophilic borylation using, in situ generated, Br-B-9-BBN. These studies highlight a new, orthogonal method of generating haloboranes and their previously unobserved role as hidden catalysts within arene borylation reactions., (© 2024 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The reduction of nitriles to primary amines is a useful transformation in organic synthesis, however, it often relies upon stoichiometric reagents or transition-metal catalysis. Herein, a borane-catalysed hydroboration of nitriles to give primary amines is reported. Good yields (48-95%) and chemoselectivity (e.g., ester, nitro, sulfone) were observed. DFT calculations and mechanistic studies support the proposal of a double B -N/ B -H transborylation mechanism., (Copyright © 2022, Meger et al.)

The mechanism of R 2 BH-catalyzed hydroboration of alkynes by 1,3,2-dioxaborolanes has been investigated by in situ 19 F NMR spectroscopy, kinetic simulation, isotope entrainment, single-turnover labeling ( 10 B/ 2 H), and density functional theory (DFT) calculations. For the Cy 2 BH-catalyzed hydroboration 4-fluorophenylacetylene by pinacolborane, the resting state is the anti-Markovnikov addition product ArCH = CHBCy 2 . Irreversible and turnover-rate limiting reaction with pinacolborane ( k ≈ 7 × 10 -3 M -1 s -1 ) regenerates Cy 2 BH and releases E -Ar-CH═CHBpin. Two irreversible events proceed in concert with turnover. The first is a Markovnikov hydroboration leading to regioisomeric Ar-C(Bpin)═CH 2 . This is unreactive to pinacolborane at ambient temperature, resulting in catalyst inhibition every ∼10 2 turnovers. The second is hydroboration of the alkenylboronate to give ArCH 2 CH(BCy 2 )Bpin, again leading to catalyst inhibition. 9-BBN behaves analogously to Cy 2 BH, but with higher anti-Markovnikov selectivity, a lower barrier to secondary hydroboration, and overall lower efficiency. The key process for turnover is B-H/C-B metathesis, proceeding by stereospecific transfer of the E -alkenyl group within a transient, μ-B-H-B bridged, 2-electron-3-center bonded B-C-B intermediate.