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 =...

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The reaction of 1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene (IDipp) with n‐BuLi in the presence of sodium and potassium bis(trimethylsilyl)amide was studied, and the resulting polymeric dicarbene species were reacted with the fluoroboranes tris(pentafluorophenyl)borane, B(C6F5)3, and tris[3,5‐bis(trifluoromethyl)phenyl]borane, B(m‐XyF6)3 to produce sodium and potassium salts of an anionic N‐heterocyclic carbene with a weakly coordinating borate moiety (WCA‐NHC).

A stable cyclobutadiene dication was isolated and structurally characterized as a bis(tribromide) salt. Unlike the folded minimum structure calculated for the parent C4H42+ system, this dication exhibits a planar geometry in the solid state. However, calculations reveal a nearly isoenergetic folded isomer, and detailed studies employing advanced NICS methods show that, counterintuitively, cyclobutadiene dications are more aromatic when puckered rather than planar. For more information on this topic and related applications of diaminoacetylenes, see the Research Article by M. Tamm and co‐workers (DOI: 10.1002/chem.202202737).

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 1,1,2,4tetramorpholino-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.