Search

The lithium salts of anionic N‐heterocyclic thiones and selones [{(WCA‐IDipp)E}Li(toluene)] (1: E=S; 2: E=Se; WCA=B(C6F5)3, IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene), which contain a weakly coordinating anionic (WCA) borate moiety in the imidazole backbone were reacted with Me3SiCl, to furnish the silylated adducts (WCA‐IDipp)ESiMe3 (3: E=S; 4: E=Se). The reaction of the latter with [(η5‐C5Me5)MCl2]2 (M=Rh, Ir) afforded the rhodium(III) and iridium(III) half‐sandwich complexes [{(WCA‐IDipp)E}MCl(η5‐C5Me5)] (5–8). The direct reaction of the lithium salts 1 and 2 with a half or a full equivalent of [M(COD)Cl]2 (M=Rh, Ir) afforded the monometallic complexes [{(WCA‐IDipp)E}M(COD)] (9–12) or the bimetallic complexes [μ2‐{(WCA‐IDipp)E}M2(COD)2(μ2‐Cl)] (13–16), respectively. The bonding situation in these complexes has been investigated by means of density functional theory (DFT) calculations, revealing thiolate or selenolate ligand character with negligible metal‐chalcogen π‐interaction. [ABSTRACT FROM AUTHOR]

Several group 16 adducts of the type [(WCA-IDipp)E]Li(solv.) that bear an anionic N-heterocyclic carbene ligand with a weakly coordinating borate moiety (WCA-IDipp, WCA = B(C6F5)3, IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene, E = O, S, Se, Te) were prepared. This was achieved by deprotonation of the corresponding ketone (IDipp)O or thione (IDipp)S with n-BuLi and subsequent reaction with B(C6F5)3 or by direct reaction of [WCA-IDipp]Li(toluene) with elemental Se or Te. The oxygen, sulfur and selenium adducts can be protonated to give derivatives (WCA-IDipp)EH (E = O, S, Se), whereas the oxidation of the sulfur and selenium adducts yielded neutral disulfide and diselenide species (WCA-IDipp)2E2 (E = S, Se). [ABSTRACT FROM AUTHOR]

Several pnictogen dihalide complexes of the type (WCA‐IDipp)EX2 (E=P, As, Sb; X=Cl, Br) that bear an anionic N‐heterocyclic carbene ligand with a weakly coordinating borate moiety (WCA‐IDipp, WCA=B(C6F5)3, IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) were prepared by salt metathesis reactions between the respective pnictogen trihalides EX3 and the lithium salt (WCA‐IDipp)Li⋅toluene. Two‐electron reduction of the dihalides (WCA‐IDipp)EX2 with 1,3‐bis(trimethylsilyl)‐1,4‐dihydropyrazine or elemental magnesium afforded the dipnictenes (WCA‐IDipp)2E2, which display typical element‐element double bonds as observed in diaryldiphosphenes, ‐arsenes and ‐stibenes. To provide an insight into the factors contributing to the structural stability of the pnictogen dihalide and dipnictene compounds, quantum chemical calculations were performed at the domain‐based local pair natural orbital coupled‐cluster (DLPNO‐CCSD(T)) level. A local energy decomposition (LED) analysis of the interaction between the carbene and the pnictogen dihalide or dipnictene moiety demonstrates that London dispersion is an essential factor for the stabilization of these compounds.London calling: Several pnictogen complexes of the type (WCA‐IDipp)EX2 and (WCA‐IDipp)2E2 (E=P, As, Sb; X=Cl, Br) that bear anionic N‐heterocyclic carbene ligands with a weakly coordinating borate moiety were prepared. To provide an insight into the factors contributing to the structural stability, quantum chemical calculations were performed involving for instance Local Energy Decomposition (LED) analysis. [ABSTRACT FROM AUTHOR]

The new diaminoacetylene (DAA) dimorpholinoacetylene (3) was prepared from 1,1-dimorpholinoethene (1) by bromination to form the dibromoketene aminal 2, which upon lithiation afforded 3 through a Fritsch-Buttenberg-Wiechell rearrangement. Heating 3 at elevated temperatures resulted in a complete conversion into the dimer 1,1,2,4-tetramorpholino-1-buten-3-yne (4), which was used for the synthesis of four-membered cyclic bent allene (CBA) transition-metal complexes of the type [(CBA)ML n ] (5-7; ML n =AuCl, RhCl(COD), RhCl(CO) 2 ; CBA=1,3,4,4-tetramorpholino-1,2-cyclobutadiene; COD=1,5-cyclooctadiene). The reaction of 3 with tetraethylammonium bromide gave 1,2,3,4-tetramorpholinocyclobutenylium bromide (8), which reacted with bromine to form 1,2,3,4-tetra(morpholino)cyclobutenediylium bis(tribromide) (9). Compound 9 represents the first fully characterized compound containing a tetraaminocyclobutadiene dication and displays a nearly planar C 4 N 4 core as shown by X-ray diffraction analysis. Detailed quantum chemical calculations were performed to assess the aromaticity of tetraaminocyclubutadiene dications by employing the Nucleus Independent Chemical Shift (NICS) method and current density analysis., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

In this Concept article we provide a brief overview of the design and preparation of N-heterocyclic carbenes carrying weakly coordinating anions (WCA-NHCs). The anionic charge in these ligand systems is located on an exocyclic group, for example, B(C 6 F 5 ) 3 , tethered to the backbone of the imidazole ring, thus resembling a weakly coordinating moiety. With the general guiding principle behind the application of WCA-NHCs being the conversion of otherwise cationic NHC complexes into their overall neutral congeners, numerous transition metal as well as main group element complexes were isolated during the last decade, which are summarized herein., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Anionic N-heterocyclic carbenes with weakly coordinating borate, aluminate, and gallate moieties of the type [(F 5 C 6 ) 3 E-NHC] - (E = B, Al, Ga) were isolated as lithium salts by the lithiation of 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (IMes) or 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (IDipp) followed by the addition of E(C 6 F 5 ) 3 (E = B, Al, Ga). Treatment with elemental selenium afforded the lithium salts of the corresponding anionic selenourea derivatives [{(F 5 C 6 ) 3 E-NHC}Se] - (NHC = IMes, E = B; NHC = IDipp, E = B, Al, Ga), which were examined, among other things, by means of 77 Se{ 1 H} NMR spectroscopy to assess the π-accepting properties of the WCA-NHC ligands in comparison with their neutral NHC congeners.

A series of group 13 complexes of the general type [{(WCA-IDipp)EX 3 }Li(solv)] (E=B, Al, Ga, In; X=Cl, Br) that bear an anionic N-heterocyclic carbene ligand with a weakly coordinating borate moiety (WCA-IDipp, WCA=B(C 6 F 5 ) 3 and IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were prepared by the reaction of the respective group 13 trihalides (EX 3 ) with the lithium salt [(WCA-IDipp)Li ⋅ toluene]. The molecular structures of the BBr 3 , AlCl 3 , AlBr 3 , GaCl 3 and InCl 3 adducts were established by X-ray diffraction analyses, revealing the formation of coordination polymers linked by halide-lithium interactions, except for the indium derivative, which consists of isolated [Li(THF) 4 ] + and [(WCA-IDipp)InCl 3 ] - ions in the solid state., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Several pnictogen dihalide complexes of the type (WCA-IDipp)EX 2 (E=P, As, Sb; X=Cl, Br) that bear an anionic N-heterocyclic carbene ligand with a weakly coordinating borate moiety (WCA-IDipp, WCA=B(C 6 F 5 ) 3 , IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were prepared by salt metathesis reactions between the respective pnictogen trihalides EX 3 and the lithium salt (WCA-IDipp)Li⋅toluene. Two-electron reduction of the dihalides (WCA-IDipp)EX 2 with 1,3-bis(trimethylsilyl)-1,4-dihydropyrazine or elemental magnesium afforded the dipnictenes (WCA-IDipp) 2 E 2 , which display typical element-element double bonds as observed in diaryldiphosphenes, -arsenes and -stibenes. To provide an insight into the factors contributing to the structural stability of the pnictogen dihalide and dipnictene compounds, quantum chemical calculations were performed at the domain-based local pair natural orbital coupled-cluster (DLPNO-CCSD(T)) level. A local energy decomposition (LED) analysis of the interaction between the carbene and the pnictogen dihalide or dipnictene moiety demonstrates that London dispersion is an essential factor for the stabilization of these compounds., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)