Tuning the Electronic Properties of Carbenes: A Systematic Comparison of Neighboring Amino versus Amido Groups

Abstract

A related series of six-membered carbenes featuring adjoining amino and/or amido groups (i.e, a diaminocarbene, a monoamido-aminocarbene (3), and a a diamidocarbene (6)) were systematically compared using crystallographic, spectroscopic, electrochemical, and density functional theory methods. The solid-state structure of 3 was found to exhibit inequivalent nitrogen− carbon bond lengths (C carbene −N amide = 1.395(4) Å vs C carbene −N amine = 1.323(4) Å). Moreover, the C carbene −N amide distance was longer than that measured in the solid-state structure of 6 (1.371(3) Å), while the C carbene −N amine distance was similar to that measured in the solid-state structure of a cyclic alkyl-aminocarbene (1.315(3) Å). Iridium complexes of the aforementioned carbenes were also evaluated, and the collected data revealed that the introduction of carbonyl groups to the carbene-containing scaffold had a nearly linear, additive effect on the E 1/2 potential of the carbene-ligated iridium I/II redox couple (+165 mV per carbonyl added) as well as the Tolman electronic parameter value of the corresponding carbene−Ir(CO) 2 Cl complex (ca. 7 cm −1 per carbonyl added). Beyond attenuated ligand donicity, the introduction of carbonyl groups was found to broaden the chemical reactivity: unlike prototypical N-heterocyclic carbenes, including diaminocarbenes, the monoamido-aminocarbene was found to couple to isonitriles to form the respective ketenimines.

Cyclische Alkylaminocarbene (CAACs): Neues von guten Bekannten

“…Heute hingegen zählen stabile Carbene zu den leistungsfähigsten Hilfsmitteln in der anorganischen, metallorganischen und organischen Chemie und haben sogar Anwendungen in den Materialwissenschaften und der Medizin gefunden . Verschiedene Singulett‐Carbene wurden bislang isoliert (Abbildung ; I – XXXVIII ), die alle, abgesehen von den Cyclopropenylidenen XXXIV und den mesoionischen Carbenen XXXVI , durch ein Phosphor‐ oder Stickstoffatom in direkter Nachbarschaft des Carbenzentrums gekennzeichnet sind. Für viele Jahre waren die N‐heterocyclischen Carbene (NHCs), d. h. Imidazolin‐2‐ylidene XII , Imidazol‐2‐ylidene XIII und 1,2,4‐Triazol‐5‐ylidene XVI , die bestuntersuchten Vertreter .…”

Isolation of a Neutral P8 Cluster by [2+2] Cycloaddition of a Diphosphene Facilitated by Carbene Activation of White Phosphorus

“…As described previously by Bertrand,7a the formation of 6 most likely results from the addition of two CDCs 1 to an initially formed species of type H . Curiously, when the carbene is changed to the less electrophilic carbene 2 ,10, 11b the product obtained is quite different (Scheme ). Indeed, when three equivalents of 2 (featuring single carbonyl) are added to P 4 in Et 2 O, an instantaneous dark green suspension is observed.…”

Development of new methods in modern selective organic synthesis: preparation of functionalized molecules with atomic precision

“…Aminoamido- (35) 264 and diamidocarbenes (36), 265 carbenes with a malonate anion moiety (37) or with a neutral alkyl malonate moiety (38) were also reported. 266,267 Structures 32 ± 38…”