@article{LorkowskiKrahfussKubickietal.2019, author = {Lorkowski, Jan and Krahfuß, Mirjam and Kubicki, Maciej and Radius, Udo and Pietraszuk, Cezary}, title = {Intramolecular Ring-Expansion Reaction (RER) and Intermolecular Coordination of In Situ Generated Cyclic (Amino)(aryl)carbenes (cAArCs)}, series = {Chemistry - A European Journal}, volume = {25}, journal = {Chemistry - A European Journal}, number = {48}, doi = {10.1002/chem.201902630}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-212496}, pages = {11365 -- 11374}, year = {2019}, abstract = {Cyclic (amino)(aryl)carbenes (cAArCs) based on the isoindoline core were successfully generated in situ by α-elimination of 3-alkoxyisoindolines at high temperatures or by deprotonation of isoindol-2-ium chlorides with sodium or copper(I) acetates at low temperatures. 3-Alkoxy-isoindolines 2 a,b-OR (R=Me, Et, iPr) have been prepared in high yields by the addition of a solution of 2-aryl-1,1-diphenylisoindol-2-ium triflate (1 a,b-OTf; a: aryl=Dipp=2,6-diisopropylphenyl; b: Mesityl-, Mes=2,4,6-trimethylphenyl) to the corresponding alcohol (ROH) with NEt3 at room temperature. Furthermore, the reaction of 2 a,b-OMe in diethyl ether with a tenfold excess of hydrochloric acid led to the isolation of the isoindol-2-ium chlorides 1 a,b-Cl in high yields. The thermally generated cAArC reacts with sulfur to form the thioamide 3 a. Without any additional trapping reagent, in situ generation of 1,1-diphenylisoidolin-3-ylidenes does not lead to the isolation of these compounds, but to the reaction products of the insertion of the carbene carbon atom into an ortho C-H bond of a phenyl substituent, followed by ring-expansion reaction; namely, anthracene derivatives 9-N(H)aryl-10-Ph-C14H8 4 a,b (a: Dipp; b: Mes). These compounds are conveniently synthesized by deprotonation of the isoindol-2-ium chlorides with sodium acetate in high yields. Deprotonation of 1 a-Cl with copper(I) acetate at low temperatures afforded a mixture of 4 a and the corresponding cAArC copper(I) chloride 5 a, and allowed the isolation and structural characterization of the first example of a cAArC copper complex of general formula [(cAArC)CuCl].}, language = {en} } @article{KraemerLuffRadiusetal.2021, author = {Kr{\"a}mer, Felix and Luff, Martin S. and Radius, Udo and Weigend, Florian and Breher, Frank}, title = {NON-Ligated N-Heterocyclic Tetrylenes}, series = {European Journal of Inorganic Chemistry}, volume = {2021}, journal = {European Journal of Inorganic Chemistry}, number = {35}, doi = {10.1002/ejic.202100446}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-262586}, pages = {3591 -- 3600}, year = {2021}, abstract = {We report on the synthesis of N-heterocyclic tetrylenes ligated by the NON-donor framework 4,5-bis(2,6-diisopropylphenyl-amino)-2,7-di-tert-butyl-9,9-dimethylxanthene. The molecular structures of the germylene (3), stannylene (4) and plumbylene (5) where determined by X-ray diffraction studies. Furthermore, we present quantum chemical studies on the σ-donor and π-acceptor properties of 3-5. Additionally, we report on the reactivity of the tetrylenes towards the transition metal carbonyls [Rh(CO)\(_{2}\)Cl]\(_{2}\), [W(CO)\(_{6}\)] and [Ni(CO)\(_{4}\)]. The isolated complexes (6 and 7) show the differing reactivity of NHTs compared to NHCs. Instead of just forming the anticipated complex [(NON)Sn-Rh(CO)\(_{2}\)Cl], 4 inserts into the Rh-Cl bond to afford [(NON)Sn(Cl)Rh(CO)(C\(_{6}\)H\(_{6}\))] (6, additional CO/C6H6 exchange) and [(NON)Sn(Cl)Rh\(_{2}\)(CO)\(_{4}\)Cl] (7). By avoiding halogenated transition metal precursors in order to prevent insertion reactions, germylene 3 shows "classical" coordination chemistry towards {Ni(CO)3} forming the complex [(NON)Ge-Ni(CO)\(_{3}\)] (8).}, language = {en} } @article{JosSzwetkowskiSlebodnicketal.2022, author = {Jos, Swetha and Szwetkowski, Connor and Slebodnick, Carla and Ricker, Robert and Chan, Ka Lok and Chan, Wing Chun and Radius, Udo and Lin, Zhenyang and Marder, Todd B. and Santos, Webster L.}, title = {Transition Metal-Free Regio- and Stereo-Selective trans Hydroboration of 1,3-Diynes: A Phosphine-Catalyzed Access to (E)-1-Boryl-1,3-Enynes}, series = {Chemistry - A European Journal}, volume = {28}, journal = {Chemistry - A European Journal}, number = {63}, doi = {10.1002/chem.202202349}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-293784}, year = {2022}, abstract = {We report a transition metal-free, regio- and stereo-selective, phosphine-catalyzed method for the trans hydroboration of 1,3-diynes with pinacolborane that affords (E)-1-boryl-1,3-enynes. The reaction proceeds with excellent selectivity for boron addition to the external carbon of the 1,3-diyne framework as unambiguously established by NMR and X-ray crystallographic studies. The reaction displays a broad substrate scope including unsymmetrical diynes to generate products in high yield (up to 95 \%). Experimental and theoretical studies suggest that phosphine attack on the alkyne is a key process in the catalytic cycle.}, language = {en} } @article{TenderaHelmKrahfussetal.2021, author = {Tendera, Lukas and Helm, Moritz and Krahfuss, Mirjam and Kuntze-Fechner, Maximilian W. and Radius, Udo}, title = {Case Study of N-\(^{i}\)Pr versus N-Mes Substituted NHC Ligands in Nickel Chemistry: The Coordination and Cyclotrimerization of Alkynes at [Ni(NHC)\(_{2}\)]}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {71}, doi = {10.1002/chem.202103093}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257137}, pages = {17849-17861}, year = {2021}, abstract = {A case study on the effect of the employment of two different NHC ligands in complexes [Ni(NHC)\(_{2}\)] (NHC=\(^{i}\)Pr\(_{2}\)Im\(^{Me}\) 1\(^{Me}\), Mes\(_{2}\)Im 2) and their behavior towards alkynes is reported. The reaction of a mixture of [Ni\(_{2}\)(\(^{i}\)Pr\(_{2}\)Im\(^{Me}\))\(_{4}\)(μ-(η\(^{2}\) : η\(^{2}\))-COD)] B/ [Ni(\(^{i}\)Pr\(_{2}\)Im\(^{Me}\))\(_{2}\)(η\(^{4}\)-COD)] B' or [Ni(Mes\(_{2}\)Im)\(_{2}\)] 2, respectively, with alkynes afforded complexes [Ni(NHC)\(_{2}\)(η\(^{2}\)-alkyne)] (NHC=\(^{i}\)Pr\(_{2}\)Im\(^{Me}\): alkyne=MeC≡CMe 3, H\(_{7}\)C\(_{3}\)C≡CC\(_{3}\)H\(_{7}\) 4, PhC≡CPh 5, MeOOCC≡CCOOMe 6, Me\(_{3}\)SiC≡CSiMe\(_{3}\) 7, PhC≡CMe 8, HC≡CC\(_{3}\)H\(_{7}\) 9, HC≡CPh 10, HC≡C(p-Tol) 11, HC≡C(4-\(^{t}\)Bu-C\(_{6}\)H\(_{4}\)) 12, HC≡CCOOMe 13; NHC=Mes\(_{2}\)Im: alkyne=MeC≡CMe 14, MeOOCC≡CCOOMe 15, PhC≡CMe 16, HC≡C(4-\(^{t}\)Bu-C\(_{6}\)H\(_{4}\)) 17, HC≡CCOOMe 18). Unusual rearrangement products 11 a and 12 a were identified for the complexes of the terminal alkynes HC≡C(p-Tol) and HC≡C(4-\(^{t}\)Bu-C\(_{6}\)H\(_{4}\)), 11 and 12, which were formed by addition of a C-H bond of one of the NHC N-\(^{i}\)Pr methyl groups to the C≡C triple bond of the coordinated alkyne. Complex 2 catalyzes the cyclotrimerization of 2-butyne, 4-octyne, diphenylacetylene, dimethyl acetylendicarboxylate, 1-pentyne, phenylacetylene and methyl propiolate at ambient conditions, whereas 1\(^{Me}\) is not a good catalyst. The reaction of 2 with 2-butyne was monitored in some detail, which led to a mechanistic proposal for the cyclotrimerization at [Ni(NHC)\(_{2}\)]. DFT calculations reveal that the differences between 1\(^{Me}\) and 2 for alkyne cyclotrimerization lie in the energy profile of the initiation steps, which is very shallow for 2, and each step is associated with only a moderate energy change. The higher stability of 3 compared to 14 is attributed to a better electron transfer from the NHC to the metal to the alkyne ligand for the N-alkyl substituted NHC, to enhanced Ni-alkyne backbonding due to a smaller C\(_{NHC}\)-Ni-C\(_{NHC}\) bite angle, and to less steric repulsion of the smaller NHC \(^{i}\)Pr\(_{2}\)Im\(^{Me}\).}, language = {en} } @article{ZapfPetersBertermannetal.2022, author = {Zapf, Ludwig and Peters, Sven and Bertermann, R{\"u}diger and Radius, Udo and Finze, Maik}, title = {Tricyanoborane-Functionalized Anionic N-Heterocyclic Carbenes: Adjustment of Charge and Stereo-Electronic Properties}, series = {Chemistry - A European Journal}, volume = {28}, journal = {Chemistry - A European Journal}, number = {39}, doi = {10.1002/chem.202200275}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-287200}, year = {2022}, abstract = {The 1-methyl-3-(tricyanoborane)imidazolin-2-ylidenate anion (2) was obtained in high yield by deprotonation of the B(CN)3-methylimidazole adduct 1. Regarding charge and stereo-electronic properties, anion 2 closes the gap between well-known neutral NHCs and the ditopic dianionic NHC, the 1,3-bis(tricyanoborane)imidazolin-2-ylidenate dianion (IIb). The influence of the number of N-bonded tricyanoborane moieties on the σ-donating and π-accepting properties of NHCs was assessed by quantum chemical calculations and verified by experimental data on 2, IIb, and 1,3-dimethylimidazolin-2-ylidene (IMe, IIa). Therefore NHC 2, which acts as a ditopic ligand via the carbene center and the cyano groups, was reacted with alkyl iodides, selenium, and [Ni(CO)\(_{4}\)] yielding alkylated imidazoles 3 and 4, the anionic selenium adduct 5, and the anionic nickel tricarbonyl complex 8, respectively. The results of this study prove that charge, number of coordination sites, buried volume (\%V\(_{bur}\)) and σ-donor and π-acceptor abilities of NHCs can be effectively fine-tuned via the number of tricyanoborane substituents.}, language = {en} } @article{HuangWuKrebsetal.2021, author = {Huang, Mingming and Wu, Zhu and Krebs, Johannes and Friedrich, Alexandra and Luo, Xiaoling and Westcott, Stephen A. and Radius, Udo and Marder, Todd B.}, title = {Ni-Catalyzed Borylation of Aryl Sulfoxides}, series = {Chemistry—A European Journal}, volume = {27}, journal = {Chemistry—A European Journal}, number = {31}, doi = {10.1002/chem.202100342}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256778}, pages = {8149-8158}, year = {2021}, abstract = {A nickel/N-heterocyclic carbene (NHC) catalytic system has been developed for the borylation of aryl sulfoxides with B\(_{2}\)(neop)\(_{2}\) (neop=neopentyl glycolato). A wide range of aryl sulfoxides with different electronic and steric properties were converted into the corresponding arylboronic esters in good yields. The regioselective borylation of unsymmetric diaryl sulfoxides was also feasible leading to borylation of the sterically less encumbered aryl substituent. Competition experiments demonstrated that an electron-deficient aryl moiety reacts preferentially. The origin of the selectivity in the Ni-catalyzed borylation of electronically biased unsymmetrical diaryl sulfoxide lies in the oxidative addition step of the catalytic cycle, as oxidative addition of methoxyphenyl 4-(trifluoromethyl)phenyl sulfoxide to the Ni(0) complex occurs selectively to give the structurally characterized complex trans-[Ni(ICy)\(_{2}\)(4-CF\(_{3}\)-C\(_{6}\)H\(_{4}\)){(SO)-4-MeO-C\(_{6}\)H\(_{4}\)}] 4. For complex 5, the isomer trans-[Ni(ICy)\(_{2}\)(C\(_{6}\)H\(_{5}\))(OSC\(_{6}\)H\(_{5}\))] 5-I was structurally characterized in which the phenyl sulfinyl ligand is bound via the oxygen atom to nickel. In solution, the complex trans-[Ni(ICy)\(_{2}\)(C\(_{6}\)H\(_{5}\))(OSC\(_{6}\)H\(_{5}\))] 5-I is in equilibrium with the S-bonded isomer trans-[Ni(ICy)\(_{2}\)(C\(_{6}\)H\(_{5}\))(SOC\(_{6}\)H\(_{5}\))] 5, as shown by NMR spectroscopy. DFT calculations reveal that these isomers are separated by a mere 0.3 kJ/mol (M06/def2-TZVP-level of theory) and connected via a transition state trans-[Ni(ICy)\(_{2}\)(C\(_{6}\)H\(_{5}\))(η\(^{2}\)-{SO}-C\(_{6}\)H\(_{5}\))], which lies only 10.8 kcal/mol above 5.}, language = {en} } @article{LiuKoleBudimanetal.2021, author = {Liu, Zhiqiang and Kole, Goutam Kumar and Budiman, Yudha P. and Tian, Ya-Ming and Friedrich, Alexandra and Luo, Xiaoling and Westcott, Stephen A. and Radius, Udo and Marder, Todd B.}, title = {Transition metal catalyst-free, base-promoted 1,2-additions of polyfluorophenylboronates to aldehydes and ketones}, series = {Angewandte Chemie International Edition}, volume = {60}, journal = {Angewandte Chemie International Edition}, number = {30}, doi = {10.1002/anie.202103686}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256487}, pages = {16529-16538}, year = {2021}, abstract = {A novel protocol for the transition metal-free 1,2-addition of polyfluoroaryl boronate esters to aldehydes and ketones is reported, which provides secondary alcohols, tertiary alcohols, and ketones. Control experiments and DFT calculations indicate that both the ortho-F substituents on the polyfluorophenyl boronates and the counterion K\(^+\) in the carbonate base are critical. The distinguishing features of this procedure include the employment of commercially available starting materials and the broad scope of the reaction with a wide variety of carbonyl compounds giving moderate to excellent yields. Intriguing structural features involving O-H⋅⋅⋅O and O-H⋅⋅⋅N hydrogen bonding, as well as arene-perfluoroarene interactions, in this series of racemic polyfluoroaryl carbinols have also been addressed.}, language = {en} } @article{BudimanWestcottRadiusetal.2021, author = {Budiman, Yudha P. and Westcott, Stephen A. and Radius, Udo and Marder, Todd B.}, title = {Fluorinated Aryl Boronates as Building Blocks in Organic Synthesis}, series = {Advanced Synthesis \& Catalysis}, volume = {363}, journal = {Advanced Synthesis \& Catalysis}, number = {9}, doi = {10.1002/adsc.202001291}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-225908}, pages = {2224 -- 2255}, year = {2021}, abstract = {Organoboron compounds are well known building blocks for many organic reactions. However, under basic conditions, polyfluorinated aryl boronic acid derivatives suffer from instability issues that are accelerated in compounds containing an ortho-fluorine group, which result in the formation of the corresponding protodeboronation products. Therefore, a considerable amount of research has focused on novel methodologies to synthesize these valuable compounds while avoiding the protodeboronation issue. This review summarizes the latest developments in the synthesis of fluorinated aryl boronic acid derivatives and their applications in cross-coupling reactions and other transformations. image}, language = {en} } @article{PhilippKrahfussRadackietal.2021, author = {Philipp, Michael S. M. and Krahfuss, Mirjam J. and Radacki, Krzysztof and Radius, Udo}, title = {N-Heterocyclic Carbene and Cyclic (Alkyl)(amino)carbene Adducts of Antimony(III)}, series = {European Journal of Inorganic Chemistry}, volume = {2021}, journal = {European Journal of Inorganic Chemistry}, number = {38}, doi = {10.1002/ejic.202100632}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257408}, pages = {4007-4019}, year = {2021}, abstract = {A systematic study on Lewis-acid/base adducts of N-heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene cAAC\(^{Me}\) (1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene) with antimony(III) chlorides of the general formula SbCl\(_{2}\)R (R=Cl, Ph, Mes) is presented. The reaction of the NHCs Me\(_{2}\)Im\(^{Me}\) (1,3,4,5-tetra-methyl-imidazolin-2-ylidene), iPr\(_{2}\)Im\(^{Me}\) (1,3-di-isopropyl-4,5-dimethyl-imidazolin-2-ylidene), Mes\(_{2}\)Im, Dipp\(_{2}\)Im (R\(_{2}\)Im=1,3-di-organyl-imidazolin-2-ylidene; Mes=2,4,6-trimethylphenyl, Dipp=2,6-di-isopropylphenyl) and cAAC\(^{Me}\) with antimony(III) compounds SbCl\(_{2}\)R (R=Cl (1), Ph (2) and Mes (3)) yields the adducts NHC ⋅ SbCl\(_{2}\)R (R=Cl (4), Ph (5) and Mes (6); NHC=Me\(_{2}\)Im\(^{Me}\) (a), iPr\(_{2}\)Im\(^{Me}\) (b), Dipp\(_{2}\)Im (c) and Mes\(_{2}\)Im (d)) and cAAC\(^{Me}\) ⋅ SbCl\(_{2}\)R (R=Cl (4 e) and Ph (5 e)). Thermal treatment of (Dipp\(_{2}\)Im) ⋅ SbCl\(_{2}\)Ar (Ar=Ph (5 c) and Mes (6 c)) in benzene leads to isomerization to the backbone coordinated \(^{a}\)NHC-adduct \(^{a}\)Dipp\(_{2}\)Im ⋅ SbCl\(_{2}\)Ar (Ar=Mes (7) and Ph (8)) (\(^{"a"}\) denotes "abnormal" coordination mode of the NHC) in high yields. One of the chloride substituents at antimony of 7 can be abstracted by GaCl3 or Ag[BF\(_{4}\)] to obtain the imidazolium salts [\(^{a}\)Dipp\(_{2}\)Im ⋅ SbClMes][BF\(_{4}\)] (9) and [\(^{a}\)Dipp\(_{2}\)Im ⋅ SbClMes][GaCl\(_{4}\)] (10).}, language = {en} } @article{BudimanFriedrichRadiusetal.2019, author = {Budiman, Yudha P. and Friedrich, Alexandra and Radius, Udo and Marder, Todd B.}, title = {Copper-catalysed Suzuki-Miyaura cross-coupling of highly fluorinated aryl boronate esters with aryl iodides and bromides and fluoroarene-arene π-stacking interactions in the products}, series = {ChemCatChem}, volume = {11}, journal = {ChemCatChem}, number = {21}, doi = {10.1002/cctc.201901220}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204839}, pages = {5387-5396}, year = {2019}, abstract = {A combination of copper iodide and phenanthroline as the ligand is an efficient catalyst for Suzuki-Miyaura cross-coupling of highly fluorinated boronate esters (aryl-Bpin) with aryl iodides and bromides to generate fluorinated biaryls in good to excellent yields. This method represents a nice alternative to traditional cross-coupling methods which require palladium catalysts and stoichiometric amounts of silver oxide. We note that π⋅⋅⋅π stacking interactions dominate the molecular packing in the partly fluorinated biaryl crystals investigated herein. They are present either between the arene and perfluoroarene, or solely between arenes or perfluoroarenes, respectively.}, language = {en} }