Boraiminolithium: An Iminoborane-Transfer Reagent

Abstract

BN/CC isosterism can give rise to attractive molecules with unique physical or chemical properties. We report here the synthesis, characterization, and reactivities of the boraiminolithium species 2, a room-temperature-stable crystalline solid accessible through a facile dehydrohalogenation/deprotonation reaction. This species, bearing a polarized BN triple bond and an anionic N center, is the first example of a BN analogue to the well-known alkynyllithium molecules (lithium acetylides). It has demonstrated a remarkable ability for iminoborane-transfer reactions, which allows for the isolation of a series of unprecedented Nfunctionalized iminoboranes as well as novel main-group heterocycles. Stable boraiminolithium reagents may become powerful tools in the exploration of new BN-containing building blocks for synthetic chemistry and materials science.

Metathesis Reactions of a NHC‐Stabilized Phosphaborene

“…The BN unit features a polarized bond, but it is particularly stable due to the strong π‐bond [10] . Iminoboranes, despite being well‐known as monomeric alkyne analogues, [11] only recently Liu and Kong have reported BN transfer reagent ( IX ), the first‐ever example of a Group 13/15 unit transfer reagent [12] . In contrast, the heavier BP‐analogues (phosphaborenes) possess a considerably weaker π‐bond, [10] and, consequently, a strong tendency to dimerize [13] .…”

“…[10] Iminoboranes, despite being well-known as monomeric alkyne analogues, [11] only recently Liu and Kong have reported BN transfer reagent (IX), the first-ever example of a Group 13/15 unit transfer reagent. [12] In contrast, the heavier BP-analogues (phosphaborenes) possess a considerably weaker π-bond, [10] and, consequently, a strong tendency to dimerize. [13] For sterically enriched systems, transient monomeric phosphaborene species can be thermally generated in solution and subsequently reacted with unsaturated organic compounds, including phenylacetylene, aldehydes, ketones, esters, or amides, to produce [2+2] cycloaddition or phosphaalkenes products, respectively.…”

Metathese Reaktionen eines NHC‐stabilisierten Phosphaborens

“…Die BN‐Einheit stellt eine polarisierte Bindung dar, ist aber, aufgrund der starken π‐Bindung, besonders stabil [10] . Iminoborane sind zwar als Alkin‐Analoga bekannt, [11] doch erst kürzlich wurde von dem ersten Beispiel eines Transferreagenzes für Gruppe 13/15‐Einheiten überhaupt (IX) durch Liu and Kong berichtet [12] . Im Gegensatz dazu haben die schwereren BP‐Analoga (Phosphaborene) eine erheblich schwächere π‐Bindung, [10] und aufgrund dessen eine starke Tendenz, zu dimerisieren [13] .…”

“…[10] Iminoborane sind zwar als Alkin-Analoga bekannt, [11] doch erst kürzlich wurde von dem ersten Beispiel eines Transferreagenzes für Gruppe 13/15-Einheiten überhaupt (IX) durch Liu and Kong berichtet. [12] Im Gegensatz dazu haben die schwereren BP-Analoga (Phosphaborene) eine erheblich schwächere π-Bindung, [10] und aufgrund dessen eine starke Tendenz, zu dimerisieren. [13] Für sterisch anspruchsvollere Systeme können transiente monomere Phosphaboren-Spezies thermisch in Lösung generiert werden und dann mit ungesättigten organischen Verbindungen, Phenylacetylene, Aldehyde, Ketone, Ester oder Amide eingeschlossen, umgesetzt werden, um [2+2]-Cycloadditionen einzugehen oder entsprechende Phosphaalken-Produkte zu produzieren.…”

Synthesis of Iminoboryl o-Carboranes by Lewis Base Promoted Aminoborirane-to-Iminoborane Isomerization

“…Since then, BN-containing compounds have attracted tremendous attention, as the replacement of CC with BN bonds has turned out to be an ingenious strategy to create novel molecules featuring unique chemical and physical properties. A variety of iminoboranes have been synthesized, allowing the expansion of the reactivity patterns − over the past half century, including adduct formation, cycloaddition with MC, EC (E = O, S, Se), CC, and RN 3 , and polar bond addition. ,,, Very recently, the Kong group reported boraiminolithium, which displayed potential in the synthesis of N-functionalized iminoboranes . However, the variation of substituents on the boron site is still of great challenge, and the scope of B-substituents is limited to alkyl, aryl, amino, silyl groups, and transition-metal fragments (Figure a).…”