American Chemical Society
ic302184h_si_002.cif (102.82 kB)

Role of Wingtip Substituents on Benzene-Platform-Based Tetrapodal Ligands toward the Formation of a Self-Assembled Silver Carbene Cage

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posted on 2013-04-15, 00:00 authored by B. Nisar Ahamed, Ranjan Dutta, Pradyut Ghosh
Tetrapodal imidazolium ligands L1L3 as their PF6 salts are synthesized in good yields by reacting 1,2,4,5-tetrakis­(bromomethyl)­benzene with N-methylimidazole, N-benzylimidazole, and N-ethylimidazole, respectively. Single-crystal X-ray diffraction studies of L1·4PF6, L2·4PF6, and L3·4PF6 show the chair conformation of the tetrapodal imidazoliums (L1L3), where 1,5- and 2,4-imidazolium moieties are oriented in opposite directions of the benzene plane. The PF6 salts of L1L3 are reacted with Ag2O to synthesize different silver complexes of N-heterocyclic carbene (NHC), 13, respectively, in good yields. Crystals of all three complexes suitable for single-crystal X-ray diffraction study are also isolated. Structural analysis of 1, i.e., the complex of L1·4PF6 containing methyl as a wingtip substituent, and Ag2O shows the formation of a bimetallic silver NHC (NHC-Ag) complex, [(L1-4H)·2Ag]·2PF6, which is rotationally disordered over an inversion of symmetry of the space group P21/c. Elemental analysis and solution-state 1H and 13C NMR studies confirm the above molecular formula of complex 1. When L2·4PF6 functionalized with the benzyl wingtip moiety is explored for similar complexation with Ag2O, the isolated complex 2 shows the formation of a simple NHC-Ag complex with molecular formula [(L2-4H)·2Ag]·2PF6, as observed in the case of 1. Interestingly, the reaction of L3·4PF6 containing ethyl as the wingtip substituent and Ag2O shows the formation of a silver-ion-assisted tetranuclear molecular box of [Ag4(L3-4H)2]4+ (3).