1,3‐Bis(tricyanoborane)imidazoline‐2‐ylidenate Anion—A Ditopic Dianionic N‐Heterocyclic Carbene Ligand

Abstract

The 1,3-bis(tricyanoborane)imidazolate anion 1 was obtained in high yield from lithium imidazolate and B(CN) 3 À pyridine adduct. Anion 1 is chemically very robust and thus allowed the isolation of the corresponding H 5 O 2 + salt. Furthermore, monoanion 1 served as starting species for the novel dianionic N-heterocyclic carbene (NHC), 1,3-bis(tricyanoborane)imidazoline-2-ylidenate anion 3 that acts as ditopic ligand via the carbene center and the cyano groups at boron. First reactions of this new NHC 3 with methyl iodide, elemental selenium, and [Ni(CO) 4 ] led to the methylated imidazolate ion 4, the dianionic selenium adduct 5, and the dianionic nickel tricarbonyl complex 6. These NHC derivatives provide a first insight into the electronic and steric properties of the dianionic NHC 3. Especially the combination of properties, such as double negative charge, different coordination sites, large buried volume and good s-donor and p-acceptor ability, make NHC 3 a unique and promising ligand and building block.

Tricyanoborane‐Functionalized Anionic N‐Heterocyclic Carbenes: Adjustment of Charge and Stereo‐Electronic Properties

“…The most significant difference was observed in the 13 C{ 1 H} NMR spectrum for the C2 nucleus. Its signal was shifted from 139.7 (1) to 205.4 ppm (Li2) or 211.9 ppm (K2), which is in the typical range observed for C carbene nuclei, for example 205.9 ppm for IIb, [12] 215.2 ppm for IIa, [24] or 211.2 ppm for D. [8] Furthermore the signal is split into a quartet due to the coupling to 11 B with 2 J( 13 C, 11 B) of 11.8 Hz. This coupling constant is close to the coupling of the two 11 B nuclei with the C2 Chemistry-A European Journal nucleus of IIb ( 2 J( 13 C, 11 B) = 11.7 Hz).…”

“…The B1 À N3 distance of 155.3 (2) pm is in the range of related B(CN) 3 Lewis base adducts, for example 157.1 pm in B(CN) 3 •py [25a] or 153.4(4)/ 155.8(4) pm in lithium 1,3-bis(tricyanoborane)imidazolate. [12] With the neutral imidazole 1 as starting material in hand, its deprotonation was investigated. Lithium and potassium hexamethyldisilazide were found to be suitable bases for the formation of the 1-methyl-3-(tricyanoborane)imidazolin-2ylidenate anion 2.…”

“…[11] Recently, we reported on the synthesis of a new type of a borane-substituted NHC, the dianionic ditopic 1,3bis(tricyanoborane)imidazolin-2-ylidenate IIb (Figure 1). [12] The reason for the unprecedented stability of dianion IIb are the B(CN) 3 moieties that are connected via B À N bonds to the central NHC core. Tricyanoborane is a Lewis superacid, [13] which explains the very robust B À N bonds and thus the stability of IIb.…”

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

“…Synthese von Li1 und Kristallstrukturen von Li1 und Li2 (thermischeE llipsoide entsprechen 25 %Aufenthaltswahrscheinlichkeit;H -Atome sind mit willkürlichen Radien gezeigt). [43] Angewandte Chemie [29] Die gute Verfügbarkeit des Lithium-und des Trimethylammonium-Salzes von 1 bildeten die Grundlage fürd ie Untersuchung der Deprotonierung von 1 zum 1,3-Bis(tricyanoboran)imidazolin-2-ylidenat-Dianion [43] Angewandte Chemie Forschungsartikel IV wurden 77 Se-NMR-Verschiebungen von 35, 87 ((CD 3 ) 2 CO) [33] und 114 ppm ([D 8 ]THF) [8c] berichtet. Die 77 Se- 13 C-Kopplungskonstante 214.5 Hz (Abbildung 6) deutet darauf hin, dass es sich bei 5 um einen guten s-Donor handelt.…”

“…Abbildung 5. Synthese von Li 2 3•thf, NMR-Spektren von Li1 und Li 2 3•thf und ein Dimer in der Kristallstruktur von 3 1 [Li 2 1(thf)]•C 6 H 6 (thermische Ellipsoide entsprechen 25 %Aufenthaltswahrscheinlichkeit;H -Atome sind mit willkürlichenR adien gezeigt;d ie H-Atome der THF-Moleküle sind weggelassen und die THF-C-Atomeals Stabmodell dargestellt) [43]. …”