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Dimorpholinoacetylene and Its Use for the Synthesis of Tetraaminocyclobutadiene Species.

Lukas KörnerLuong Phong HoRalph PuchtaAmnon StangerMatthias Tamm
Published in: Chemistry (Weinheim an der Bergstrasse, Germany) (2022)
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.
Keyphrases
  • transition metal
  • molecular dynamics
  • high resolution
  • crystal structure