Aspects of Nucleophilic Carbene Chemistry

Abstract

Fig. 23. "Quantasomes" from spinach chloroplasts; 880 8, diameter polystyrene latex marker molecules made up of fairly uniform oblate spheroids which we have called "quantasomes" ; this work was performed by Drs. Roderic B. Park and Ning G. Pon. Within these quantosomes the chlorophyll itself is highly organized, as we have been able to demonstrate, particularly by the electric dichroism experiments performed by Dr. Kenneth H. Sauer [23].We are now in the midst of trying to determine precisely what happens after the chiorophyll has absorbed the quantum to become an excited chlorophyll molecule, a problem that involves the physicist and physical chemist as well as organic and biochemists. The determination of the next stage in the energy conversion process is one of our immediate concerns. It is either an electron transfer process [20], and thus comes close in its further stages to the electron transfer processes which are being explored in mitochondria [24], or it is some independent nonredox method of energy conversion [21]. This remains for the future to decide.Chemical biodynamics, involving as it does the fusion of many scientific disciplines, will play a role in this problem, as it already has done in the elucidation of the carbon cycle. It can be expected to take an increasingly important place towards the understanding on a molecular level of the dynamics of living organisms. Bis [ I ,3-diphenyl-2-imidazolidinylidene] shows a considerable tendency towards dissociation into two carbenes. Reactions with this easily accessible carbene source lead to an understanding of nucleophilic carbene chemistry. The question of the existence of particularly stable carbenes is discussed, and it is suggested that a surprisingly large area of preparative possibilities and theoretical knowledge awaits development.

Evidence for an Equilibrium between an N-heterocyclic Carbene and Its Dimer in Solution

“…The simultaneous detection of 3 d and (3 d) 2 by NMR spectroscopy in a solution prepared from pure (3 d) 2 constituted evidence of the equilibrium between the N-heterocyclic carbene and the corresponding enetetramine as well as the dissociation of the enetetramine into two carbenes in a direct route, rather than the indirect route via the metathesis products. We are convinced that catalytically active electrophiles were absent under the reaction conditions specified.…”

“…Dedicated to Professor Wolf-Peter Fehlhammer on the occasion of his 60th birthday Shortly after the isolation of the first stable N-heterocyclic carbene 1 (derived from imidazole), [1] the synthesis and characterization of saturated carbenes 2 (derived from imidazoline and postulated by Wanzlick more than 40 years ago [2] ) was successfully carried out. [3] However, carbenes of type 2 were not prepared by the dissociation of electron-rich enetetramines (2) 2 as suggested by Wanzlick (Scheme 1); they were obtained by deprotonation of imidazolinium salts [3a] or by reduction of imidazoline-2-thiones.…”

Copper(I) carbene hydride complexes acting both as reducing agent and precursor for Cu ALD: a study through density functional theory

“…mercury, copper and isothiocyanate [18][19][20]. Copper carbene complexes have a number of uses in organic chemistry.…”

Advances in the Knowledge of N-Heterocyclic Carbenes Properties. The Backing of the Electrochemical Investigation

“…Nevertheless, since the investigations of Wanzlich in 1968 [12], the subsequent studies of (Bertrand and coworkers, 1998) [13] and especially thanks to the isolation and characterization of 1,3-di(adamantyl)imidazole-2-ylidene (Arduengo and coworkers, 1991) [14], NHCs are regarded as organic structures of considerable significance.…”