Das 1,3‐Bis(tricyanoboran)imidazolin‐2‐ylidenat‐Anion – Ein ditopischer dianionischer N‐heterocyclischer Carben‐Ligand

Abstract

Das 1,3‐Bis(tricyanoboran)imidazolat‐Anion 1 wurde in hoher Ausbeute ausgehend von Lithiumimidazolat und B(CN)3‐Pyridin‐Addukt erhalten. Das Anion 1 ist chemisch sehr robust, was sich in der Isolierung des H5O2+‐Salzes widerspiegelt. Ferner dient 1 als Startmaterial für das neuartige dianionische N‐heterocyclische Carben (NHC), das 1,3‐Bis(tricyanoboran)imidazolin‐2‐ylidenat‐Anion 3, das mit seinem Carben‐Kohlenstoffatom und den Cyano‐Gruppen an Bor ein ditopischer Ligand ist. Erste Reaktionen des neuen NHC 3 mit Methyliodid, elementarem Selen und [Ni(CO)4] gaben das methylierte Imidazolat‐Ion 4, das dianionische Selen‐Addukt 5 und den dianionischen Nickeltricarbonyl‐Komplex 6. Diese NHC‐Derivate geben erste Einblicke in die elektronischen und sterischen Eigenschaften von 3. Insbesondere die Kombination von Eigenschaften – wie die zweifach negative Ladung, verschiedene Donorzentren, ein großes verdecktes Volumen und gute σ‐Donor‐ und π‐Akzeptor‐Eigenschaften – macht NHC 3 zu einem einzigartigen und vielversprechenden Liganden und Baustein.

Boranes Paving the Way to Anionic Cyclic (Alkyl)(amino)carbenes (Ani‐cAACs)

“…The small 1 J( 77 Se, 13 C) coupling constant of Li8 • (THF) 1.5 of 206.0 Hz underlines the strong σ-donor ability of 6 compared to Ani-cAAC-B(CN) 3 , which is 5) pm [20] and IB(CN) 3 2À (III) d(C=Se) = 184.2(4) pm. [14] The Li ion in Li8 • (THF) 2 is tetrahedrally coordinated by the O atoms of two THF ligands, the boron bonded fluorine substituent F1, and Se1.…”

“…So, it is larger than %V bur reported for cAAC Me -5 (38.0 %) [34] and identical to %V bur reported for IB(CN) 3 2À (III). [14] Noteworthy, a significantly larger %V bur of 43.3 % was evaluated for 6 from the structural parameters of the selenium compound Li8 • (THF) 2 (see steric maps in the SI). This difference in %V bur is attributed to the rotational freedom of the C 2 F 5 BF 2 unit, rendering Ani-cAAC 6 a ligand with a flexible steric environment.…”

“…Herein, we report on a straightforward high yield strategy towards anionic cAACs, using the modular synthetic strategy towards tricyanoborane-substituted imidazoline-2-ylidenate anions developed by us, earlier. [14,20] The synthesis relies on literature-known Lewis basic hydropyridines [27] and different borane adducts as key starting compounds. Thus, a tedious multistep ring closure synthesis, as currently used for the preparation of neutral cAACs, was circumvented.…”

“…The unprecedented stereo‐electronic properties of the tricyanoborane substituted anionic NHCs III and IV stimulated our interest in related, so far unknown anionic cAACs (Ani‐cAACs, Figure 1). Herein, we report on a straightforward high yield strategy towards anionic cAACs, using the modular synthetic strategy towards tricyanoborane‐substituted imidazoline‐2‐ylidenate anions developed by us, earlier [14,20] . The synthesis relies on literature‐known Lewis basic hydropyridines [27] and different borane adducts as key starting compounds.…”

N-Heterocyclic carbene and cyclic (alkyl)(amino)carbene complexes of vanadium(iii) and vanadium(v)

“…Tamm, Nomura and coworkers demonstrated that anionic NHC ligands 16 featuring a B(C 6 F 5 ) 3 moiety in the NHC backbone can substitute a chloride ligand of [V(NR)Cl 3 ] to yield vanadium( v ) imido complexes [V(NR)Cl 2 (WCA-NHC)] (WCA = B(C 6 F 5 ) 3 , R = adamantyl, phenyl, 2,6-dimethylphenyl). These complexes are active catalysts for the ethylene polymerization in presence of Al i Bu 3 .…”