1280193-45-4Relevant academic research and scientific papers
Preparation of 2-alkylidene-substituted 1,3,4,5-tetramethylimidazolines and their reactivity towards RhI Complexes and B(C6F 5)3
Kronig, Sabrina,Jones, Peter G.,Tamm, Matthias
, p. 2301 - 2314 (2013)
In addition to the known 1,3,4,5-tetramethyl-2-methyleneimidazoline (1a), which exhibits a highly polarized exocyclic C-C bond, a series of novel 2-alkylidene-substituted 1,3,4,5-tetramethylimidazolines 1b-e were synthesized and characterized. The molecular structures of 1b, 1d, and 1e were determined by X-ray diffraction analysis and revealed an increase in the polarization of the exocyclic C-C bond with increasing steric demand of the 2-substituent. On the basis of their ylidic nature, 1a-e show enhanced basicity and reactivity towards Lewis acidic centers. Treatment of 1a and 1b with [{RhCl(cod)}2] or B(C6F5)3 afforded complexes of the type [(L)RhCl(cod)] (4a,b), [(L)RhCl(CO)2] (7a,b) (L = 1a,b) or classical Lewis acid/base adducts [(1a)B(C6F5)3] (8a) and [(1b)B(C6F5)3] (8b). In contrast, complexes [(L)RhCl(cod)] with 1c and 1d as ligands are not stable, and imidazolium dichlororhodate salts 6a and 6b were isolated instead. Rhodium-alkyl complexes 5a and 5b are assumed to be intermediates in this decomposition process, and 5a was characterized by X-ray diffraction analysis. Furthermore, treatment of 1c and 1d with B(C6F5)3 did not afford classical Lewis adducts, and instead imidazolium hydridoborate salts 9a and 9b are formed by hydride abstraction. Surprisingly, we found that 1e does not react with [{RhCl(cod)}2] and forms an abnormal Lewis adduct 10 when treated with B(C6F5)3. Several 1,3,4,5-tetramethyl-2- alkylideneimidazolines were prepared, and their reactivity towards Rh I complexes and B(C6F5) was studied. Depending on the alkylidene substituent, diverse reaction patterns were observed that involved not only coordination through the exocyclic carbon atom, but also formation of unusual adducts as illustrated for the CPh2 derivative and its reaction with B(C6F5)3. Copyright
