<i>N</i>,<i>N</i>‘-Diferrocenyl-<i>N</i>-heterocyclic Carbenes and Their
Derivatives
Benno Bildstein
Michael Malaun
Holger Kopacka
Klaus Wurst
Martin Mitterböck
Karl-Hans Ongania
Giuliana Opromolla
Piero Zanello
10.1021/om990377h.s003
https://acs.figshare.com/articles/journal_contribution/_i_N_i_i_N_i_-Diferrocenyl-_i_N_i_-heterocyclic_Carbenes_and_Their_Derivatives/3785166
In continuation of our work on Wanzlick/Arduengo carbenes containing redox-active
ferrocenyl substituents we report on the synthesis of <i>N</i>,<i>N</i>‘-diferrocenyl imidazol(in)ium salts
as precursors of imidazol(in)-2-ylidenes. The necessary starting material for this chemistry
is aminoferrocene, which was prepared by an improved and large-scale synthesis by the
sequence solid lithioferrocene, iodoferrocene, <i>N</i>-ferrocenylphthalimide, aminoferrocene. The
preparation of <i>N</i>,<i>N</i>‘-diferrocenyl heterocycles involves condensation of aminoferrocene with
glyoxal to afford <i>N</i>,<i>N</i>‘-diferrocenyldiazabutadiene [Fc-DAB], reduction, condensation with
formaldehyde, and oxidation with trityl salts to yield <i>N</i>,<i>N</i>‘-diferrocenylimidazol(in)ium salts.
In situ deprotonation and trapping with electrophiles yielded the expected metal complexes
and derivatives in some cases [Ag<sup>+</sup> or S<sub>8</sub>], but attempted reaction with other transition metals
[e.g., Pd(II)] failed to give the corresponding complexes, due to (i) steric hindrance by the
two <i>N</i>-ferrocenyl substituents, (ii) reduced acidity of the imidazol(in)ium precursors, and
(iii) inaccessibility of the free carbenes. Spectroscopic [IR, Raman, UV−vis, MS, NMR (<sup>1</sup>H,
<sup>13</sup>C, <sup>109</sup>Ag)], structural [X-ray], and electrochemical [CV] properties are reported and compared
to those of other <i>N</i>-heterocyclic carbene derivatives.
1999-09-16 00:00:00
metal complexes
heterocyclic carbene derivatives
13 C
ferrocenyl substituents
trityl salts
aminoferrocene
precursor
heterocyclic Carbenes
MS
transition metals
diferrocenyl
synthesis
1 H
imidazol
CV
NMR
UV
steric hindrance
IR
condensation
Ag