Synthesis of an Extremely Bent Acyclic Allene (A “Carbodicarbene”): A Strong Donor Ligand

Abstract

Bis ans Limit: Werden CC‐π‐Bindungen durch Push‐push‐Substitution aufs Äußerste gespannt, so entstehen gebogene Allene (siehe Struktur; C türkis, N blau). In einem acyclischen Allen beträgt der CCC‐Bindungswinkel nur noch 134.8°; das üblicherweise sp‐hybridisierte zentrale Kohlenstoffatom nähert sich daher einer Konfiguration mit zwei freien Elektronenpaaren an und wirkt als sehr starker η1‐Donorligand für Übergangsmetallzentren.

Recent Advances in the Field of Main‐Group Mono‐ and Diatomic “Allotropes” Stabilised by Neutral Ligands

“…[11] The group of Bertrand met this challenge a year later, with the synthesis of the "bent allene" (2 a), which can be interpreted as an NHC-stabilised C 1 , represented by dative model 2 b. [4] Theoretical studies have also accompanied all of the synthetic reports, allowing for a more complete understanding of the bonding and electronic structure within the complexes.…”

“…As often happens in p-block chemistry, C and N are outliers; their syntheses proceeds by means of deprotonation of dicationic precursors generated by organic protocols. [4,14] Some phosphorus(0) compounds could also be considered outliers synthetically, being generated by carbene activation of P 4 . [8,9] Activation of P 4 by carbenes and other main-group compounds has been reviewed.…”

“…Compounds 1-5 are representative examples of syntheses achieved prior to the material that forms the focus of this review. Successful isolations have been carried out for C 1 , [4] Si 2 , [2] Ge 2 , [5] P 2 , [6] and As 2 [7] stabilised by NHC (Ar 2 NHC; Ar = 2,6-diispropylphenyl in most cases) ligands, and P 1 /P 2 by the cyclic alkyl amino carbene ligand (CAAC, for example, 5). [8] Stabilisation of larger P n fragments and clusters by either NHC or CAAC ligands has also been accomplished.…”

Synthesis and Ligand Properties of Stable Five‐Membered‐Ring Allenes Containing Only Second‐Row Elements

“…[1] Because of their rigidity, allene frameworks can only be accommodated into a ring with difficulty, and calculations predict that the ring strain increases considerably with each successive removal of a carbon atom from the backbone of cyclic allenes [from 1,2-cyclooctadiene (12 kcal mol À1 ) to 1,2-cyclobutadiene (90 kcal mol À1 )]. [2] We showed recently [9] that a push-push substitution pattern [10] can induce a severe deviation from the classical geometry of acyclic allenes. [4] The kinetically protected 1,2-cyclooctadiene A 3 (calculated C-C-C angle: 1588), [5] the trisilicon- [6] and diphosphorus-containing [7] hexacycles A 4 -A 6 (crystallographically observed C-C-C angles: 166, 161, and 1568, respectively; Mes = mesityl), and the recently isolated five-membered halfnium-containing allenoid A 7 (C-C-C angle: 1568) [8] are the most bent cyclic allenes isolated to date.…”

Observation of Carbodicarbene Ligand Redox Noninnocence in Highly Oxidized Iron Complexes

“…[1] Their utility has spurred intense efforts to explore the chemistry of carbon compounds possessing unusual valency.O ne of the more recent additions to this class of compounds are carbodicarbenes (CDCs), also referred to as bent allenes, which were first synthesized by the groups of Bertrand [2] and Fürstner [3] in 2008. [1] Their utility has spurred intense efforts to explore the chemistry of carbon compounds possessing unusual valency.O ne of the more recent additions to this class of compounds are carbodicarbenes (CDCs), also referred to as bent allenes, which were first synthesized by the groups of Bertrand [2] and Fürstner [3] in 2008.…”