TY - JOUR A1 - Huang, Mingming A1 - Hu, Jiefeng A1 - Krummenacher, Ivo A1 - Friedrich, Alexandra A1 - Braunschweig, Holger A1 - Westcott, Stephen A. A1 - Radius, Udo A1 - Marder, Todd B. T1 - Base-Mediated Radical Borylation of Alkyl Sulfones JF - Chemistry—A European Journal N2 - A practical and direct method was developed for the production of versatile alkyl boronate esters via transition metal-free borylation of primary and secondary alkyl sulfones. The key to the success of the strategy is the use of bis(neopentyl glycolato) diboron (B\(_{2}\)neop\(_{2}\)), with a stoichiometric amount of base as a promoter. The practicality and industrial potential of this protocol are highlighted by its wide functional group tolerance, the late-stage modification of complex compounds, no need for further transesterification, and operational simplicity. Radical clock, radical trap experiments, and EPR studies were conducted which show that the borylation process involves radical intermediates. KW - boron KW - boronate KW - boronic acid KW - metal-free KW - radical Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257281 VL - 28 IS - 3 ER - TY - JOUR A1 - Lindl, Felix A1 - Guo, Xueying A1 - Krummenacher, Ivo A1 - Rauch, Florian A1 - Rempel, Anna A1 - Paprocki, Valerie A1 - Dellermann, Theresa A1 - Stennett, Tom E. A1 - Lamprecht, Anna A1 - Brückner, Tobias A1 - Radacki, Krzysztof A1 - Bélanger-Chabot, Guillaume A1 - Marder, Todd B. A1 - Lin, Zhenyang A1 - Braunschweig, Holger T1 - Rethinking Borole Cycloaddition Reactivity JF - Chemistry—A European Journal N2 - Boroles are attracting broad interest for their myriad and diverse applications, including in synthesis, small molecule activation and functional materials. Their properties and reactivity are closely linked to the cyclic conjugated diene system, which has been shown to participate in cycloaddition reactions, such as the Diels-Alder reaction with alkynes. The reaction steps leading to boranorbornadienes, borepins and tricyclic boracyclohexenes from the thermal reaction of boroles with alkynes are seemingly well understood as judged from the literature. Herein, we question the long-established mechanistic picture of pericyclic rearrangements by demonstrating that seven-membered borepins (i. e., heptaphenylborepin and two derivatives substituted with a thienyl and chloride substituent on boron) exist in a dynamic equilibrium with the corresponding bicyclic boranorbornadienes, the direct Diels-Alder products, but are not isolable products from the reactions. Heating gradually converts the isomeric mixtures into fluorescent tricyclic boracyclohexenes, the most stable isomers in the series. Results from mechanistic DFT calculations reveal that the tricyclic compounds derive from the boranorbornadienes and not the borepins, which were previously believed to be intermediates in purely pericyclic processes. KW - pericyclic reaction KW - Boron KW - computational chemistry KW - isomer KW - isomerization Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256888 VL - 27 IS - 43 ER - TY - JOUR A1 - Heß, Merlin A1 - Krummenacher, Ivo A1 - Dellermann, Theresa A1 - Braunschweig, Holger T1 - Rhodium-Mediated Stoichiometric Synthesis of Mono-, Bi-, and Bis-1,2-Azaborinines: 1-Rhoda-3,2-azaboroles as Reactive Precursors JF - Chemistry—A European Journal N2 - A series of highly substituted 1,2-azaborinines, including a phenylene-bridged bis-1,2-azaborinine, was synthesized from the reaction of 1,2-azaborete rhodium complexes with variously substituted alkynes. 1-Rhoda-3,2-azaborole complexes, which are accessible by phosphine addition to the corresponding 1,2-azaborete complexes, were also found to be suitable precursors for the synthesis of 1,2-azaborinines and readily reacted with alkynyl-substituted 1,2-azaborinines to generate new regioisomers of bi-1,2-azaborinines, which feature directly connected aromatic rings. Their molecular structures, which can be viewed as boron-nitrogen isosteres of biphenyls, show nearly perpendicular 1,2-azaborinine rings. The new method using rhodacycles instead of 1,2-azaborete complexes as precursors is shown to be more effective, allowing the synthesis of a wider range of 1,2-azaborinines. KW - structure elucidation KW - azaborinines KW - nitrogen heterocycles KW - cyclization KW - metallacycles Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256830 VL - 27 IS - 37 ER - TY - JOUR A1 - Gärtner, Annalena A1 - Marek, Matthäus A1 - Arrowsmith, Merle A1 - Auerhammer, Dominic A1 - Radacki, Krzysztof A1 - Prieschl, Dominic A1 - Dewhurst, Rian D. A1 - Braunschweig, Holger T1 - Boron- versus Nitrogen-Centered Nucleophilic Reactivity of (Cyano)hydroboryl Anions: Synthesis of Cyano(hydro)organoboranes and 2-Aza-1,4-diborabutatrienes JF - Chemistry—A European Journal N2 - Cyclic alkyl(amino)carbene-stabilized (cyano)hydroboryl anions were synthesized by deprotonation of (cyano)dihydroborane precursors. While they display boron-centered nucleophilic reactivity towards organohalides, generating fully unsymmetrically substituted cyano(hydro)organoboranes, they show cyano-nitrogen-centered nucleophilic reactivity towards haloboranes, resulting in the formation of hitherto unknown linear 2-aza-1,4-diborabutatrienes. KW - nucleophile KW - boron KW - boryl anion KW - cumulene Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256853 VL - 27 IS - 37 ER - TY - JOUR A1 - Huang, Zhenguo A1 - Wang, Suning A1 - Dewhurst, Rian D. A1 - Ignat'ev, Nikolai V. A1 - Finze, Maik A1 - Braunschweig, Holger T1 - Boron: Its Role in Energy‐Related Processes and Applications JF - Angewandte Chemie International Edition N2 - Boron's unique position in the Periodic Table, that is, at the apex of the line separating metals and nonmetals, makes it highly versatile in chemical reactions and applications. Contemporary demand for renewable and clean energy as well as energy‐efficient products has seen boron playing key roles in energy‐related research, such as 1) activating and synthesizing energy‐rich small molecules, 2) storing chemical and electrical energy, and 3) converting electrical energy into light. These applications are fundamentally associated with boron's unique characteristics, such as its electron‐deficiency and the availability of an unoccupied p orbital, which allow the formation of a myriad of compounds with a wide range of chemical and physical properties. For example, boron's ability to achieve a full octet of electrons with four covalent bonds and a negative charge has led to the synthesis of a wide variety of borate anions of high chemical and electrochemical stability—in particular, weakly coordinating anions. This Review summarizes recent advances in the study of boron compounds for energy‐related processes and applications. KW - boron KW - electrolytes KW - hydrogen KW - OLEDs KW - small-molecule activation Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-218514 VL - 59 IS - 23 SP - 8800 EP - 8816 ER - TY - JOUR A1 - Lu, Wei A1 - Jayaraman, Arumugam A1 - Fantuzzi, Felipe A1 - Dewhurst, Rian D. A1 - Härterich, Marcel A1 - Dietz, Maximilian A1 - Hagspiel, Stephan A1 - Krummenbacher, Ivo A1 - Hammond, Kai A1 - Cui, Jingjing A1 - Braunschweig, Holger T1 - An unsymmetrical, cyclic diborene based on a chelating CAAC ligand and its small-molecule activation and rearrangement chemistry JF - Angewandte Chemie International Edition N2 - A one-pot synthesis of a CAAC-stabilized, unsymmetrical, cyclic diborene was achieved via consecutive two-electron reduction steps from an adduct of CAAC and B\(_2\)Br\(_4\)(SMe\(_2\))\(_2\). Theoretical studies revealed that this diborene has a considerably smaller HOMO–LUMO gap than those of reported NHC- and phosphine-supported diborenes. Complexation of the diborene with [AuCl(PCy\(_3\))] afforded two diborene–Au\(^I\) π complexes, while reaction with DurBH\(_2\), P\(_4\) and a terminal acetylene led to the cleavage of B−H, P−P, and C−C π bonds, respectively. Thermal rearrangement of the diborene gave an electron-rich cyclic alkylideneborane, which readily coordinated to Ag\(^I\) via its B=C double bond. KW - inorganic chemistry KW - thermal rearrangement KW - alkylideneborane KW - carbene KW - diborene Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256576 VL - 61 IS - 3 ER - TY - JOUR A1 - Härterich, Marcel A1 - Matler, Alexander A1 - Dewhurst, Rian D. A1 - Sachs, Andreas A1 - Oppel, Kai A1 - Stoy, Andreas A1 - Braunschweig, Holger T1 - A step-for-step main-group replica of the Fischer carbene synthesis at a borylene carbonyl JF - Nature Communications N2 - The Fischer carbene synthesis, involving the conversion of a transition metal (TM)-bound CO ligand to a carbene ligand of the form [=C(OR’)R] (R, R’ = organyl groups), is one of the seminal reactions in the history of organometallic chemistry. Carbonyl complexes of p-block elements, of the form [E(CO)n] (E = main-group fragment), are much less abundant than their TM cousins; this scarcity and the general instability of low-valent p-block species means that replicating the historical reactions of TM carbonyls is often very difficult. Here we present a step-for-step replica of the Fischer carbene synthesis at a borylene carbonyl involving nucleophilic attack at the carbonyl carbon followed by electrophilic quenching at the resultant acylate oxygen atom. These reactions provide borylene acylates and alkoxy-/silyloxy-substituted alkylideneboranes, main-group analogues of the archetypal transition metal acylate and Fischer carbene families, respectively. When either the incoming electrophile or the boron center has a modest steric profile, the electrophile instead attacks at the boron atom, leading to carbene-stabilized acylboranes – boron analogues of the well-known transition metal acyl complexes. These results constitute faithful main-group replicas of a number of historical organometallic processes and pave the way to further advances in the field of main-group metallomimetics. KW - chemical bonding KW - ligands Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-357270 VL - 14 ER - TY - JOUR A1 - Schmidt, Paul A1 - Fantuzzi, Felipe A1 - Klopf, Jonas A1 - Schröder, Niklas B. A1 - Dewhurst, Rian D. A1 - Braunschweig, Holger A1 - Engel, Volker A1 - Engels, Bernd T1 - Twisting versus delocalization in CAAC- and NHC-stabilized boron-based biradicals: the roles of sterics and electronics JF - Chemistry - A European Journal N2 - Twisted boron-based biradicals featuring unsaturated C\(_2\)R\(_2\) (R=Et, Me) bridges and stabilization by cyclic (alkyl)(amino)carbenes (CAACs) were recently prepared. These species show remarkable geometrical and electronic differences with respect to their unbridged counterparts. Herein, a thorough computational investigation on the origin of their distinct electrostructural properties is performed. It is shown that steric effects are mostly responsible for the preference for twisted over planar structures. The ground-state multiplicity of the twisted structure is modulated by the σ framework of the bridge, and different R groups lead to distinct multiplicities. In line with the experimental data, a planar structure driven by delocalization effects is observed as global minimum for R=H. The synthetic elusiveness of C\(_2\)R\(_2\)-bridged systems featuring N-heterocyclic carbenes (NHCs) was also investigated. These results could contribute to the engineering of novel main group biradicals. KW - chemistry KW - radicals KW - ab initio calculations KW - boron KW - carbene ligands KW - density functional calculations Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256636 VL - 27 IS - 16 ER - TY - JOUR A1 - Dietz, Maximilian A1 - Arrowsmith, Merle A1 - Reichl, Stephan A1 - Lugo‐Fuentes, Leonardo I. A1 - Jiménez‐Halla, J. Oscar C. A1 - Scheer, Manfred A1 - Braunschweig, Holger T1 - Stable Two‐Legged Parent Piano‐Stool and Mixed Diborabenzene‐E\(_{4}\) (E=P, As) Sandwich Complexes of Group 8 JF - Angewandte Chemie International Edition N2 - A cyclic alkyl(amino)carbene‐stabilized 1,4‐diborabenzene (DBB) ligand enables the isolation of 18‐electron two‐legged parent piano‐stool Fe\(^{0}\) and Ru\(^{0}\) complexes, [(η\(^{6}\)‐DBB)M(CO)\(_{2}\)], the ruthenium complex being the first of its kind to be structurally characterized. [(η\(^{6}\)‐DBB)Fe(CO)\(_{2}\)] reacts with E\(_{4}\) (E=P, As) to yield mixed DBB‐cyclo‐E\(_{4}\) sandwich complexes with planar E\(_{4}\)\(^{2-}\) ligands. Computational analyses confirm the strong electron‐donating capacity of the DBB ligand and show that the E\(_{4}\) ligand is bound by four equivalent Fe−P σ bonds. KW - 1,4-Diborabenzene KW - bonding KW - group 8 metals KW - Parent Piano-Stool Complex KW - Pnictogen reduction Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-293880 VL - 61 IS - 36 ER - TY - JOUR A1 - Matler, Alexander A1 - Arrowsmith, Merle A1 - Schorr, Fabian A1 - Hermann, Alexander A1 - Hofmann, Alexander A1 - Lenczyk, Carsten A1 - Braunschweig, Holger T1 - Reactivity of Terminal Iron Borylenes and Bis(borylenes) with Carbodiimides: Cycloaddition, Metathesis, Insertion and C−H Activation Pathways JF - European Journal of Inorganic Chemistry N2 - The reactions of carbodiimides with the iron arylborylene complex [Fe=BDur(CO)\(_{3}\)(PMe\(_{3}\))] (Dur=2,3,5,6-Me\(_{4}\)C\(_{6}\)H) and the iron bis(borylene) complex [Fe{=BDur}{=BN(SiMe\(_{3}\))\(_{2}\)}(CO)\(_{3}\)] yield a wide variety of temperature-dependent products, including known FeBNC and novel FeBNB metallacycles, complexes of N-heterocyclic boracarbene and spiro-boracarbene ligands and a unique 1,3,2,4-diazadiborolyl pianostool complex, characterized by NMR spectroscopy and X-ray crystallography. The product distributions can be rationalized by considering sequences of cycloaddition, metathesis, insertion, and C−H activation pathways mainly governed by sterics. KW - structure elucidation KW - borylene complexes KW - cycloaddition KW - metathesis KW - reaction mechanisms Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257397 VL - 2021 IS - 45 ER -