The “Wanzlick Equilibrium”

Silver(i) N-Heterocyclic Carbenes

“…[3] Based on these results, Herrmann stated that Wanzlick's equilibrium exists between stable carbenes and the corresponding eneteramines and that the equilibrium depends on several factors. [4] Wanzlick, again in 1970, noticed that deprotonation of an imidazolium salt by potassium tertiary butoxide yielded an imidazol-2-ylidene, which, however, was trapped but not isolated. [5] Nevertheless his contributions in the chemistry of NHCs stimulated much related research.…”

Synthesis of electron-rich platinum centers: Platinum0(carbene)(alkene)2 complexes

“…Recently, the equilibrium between monomer and dimer proposed by Wanzlick [25] has indeed been observed by Hahn et al and Lemal et al [26][27][28]. These authors were actually able to observe a mixture of the dimer and monomer by 1 H NMR spectroscopy, by using sterically larger aromatic N-substituents.…”

“…We added dihydrogen gas to the reaction mixture to see if the putative compound 6ax could be trapped by reaction with H 2 . This reaction was carried out in acetone-d 6 in an NMR tube and was followed (4) C(1)-Pt(1)-C (22) 96.96(10) C(1)-Pt(1)-C (28) 94.21(10) C(1)-Pt(1)-C (23) 136.16(10) C(1)-Pt(1)-C (29) 133.38 (10) by 1 H NMR spectroscopy. Indeed platinum hydrides were observed in the expected chemical shift-range similarly to known analogues [21] at about À14.5 ppm, indicating a hydride trans to an iodide, as in trans-hydrido 3,5-dimethyl-imidazol-2-yliden iodo 3,5-dimesitylimidazol-2-yliden platinum(II) (6ay) after reductive elimination of methane.…”

NHC ligands versus cyclopentadienyls and phosphines as spectator ligands in organometallic catalysis

“…Such methods are less easy to apply to chelate bis-imidazolium salts because free NHCs tend to dimerize by the Wanzlick equilibrium (Eq. (1)) [16]. Perhaps because the equilibrium very much favors the dimer, this dimer has not proved generally useful for synthesis of NHC complexes, although notable exceptions exist [17].…”