Main Group Multiple Bonds for Bond Activations and Catalysis

Abstract

Since the discovery that the so‐called “double‐bond” rule could be broken, the field of molecular main group multiple bonds has expanded rapidly. With the majority of homodiatomic double and triple bonds realised within the p‐block, along with many heterodiatomic combinations, this Minireview examines the reactivity of these compounds with a particular emphasis on small molecule activation. Furthermore, whilst their ability to act as transition metal mimics has been explored, their catalytic behaviour is somewhat limited. This Minireview aims to highlight the potential of these complexes towards catalytic application and their role as synthons in further functionalisations making them a versatile tool for the modern synthetic chemist.

Synthesis and Reactivity of Acyclic Germanimines: Silyl Rearrangement and Cycloadditions

“…Investigations into compounds containing multiple bonds between main group elements have evolved from structural curiosity to active catalysis over the past four decades. − Although postulated to behave as reactive substrates, − early germanimine complexes (L 2 GeNR) were unstable and reactive; hence, their existence was postulated through trapping reactions with polar unsaturated molecules . The reported reactivity studies typically involved dialkyl- or diaryl-germanimines engaging in 1,2-addition (including [2+2] cycloaddition) reactions with substrates across the polar GeN multiple bond, similar to that observed with transition metal imido complexes. − …”

Carbon–chalcogen bond formation initiated by [Al(NONDipp)(E)]−anions containing Al–E{16} (E{16} = S, Se) multiple bonds

“… 5 Furthermore there has been an important shift in the focus of main group research away from being directed solely at the isolation of challenging synthetic targets of academic interest, and towards exploiting the reactivity of these systems in new chemical applications. 6 …”

NHC-Stabilized 1,2-Dihalodiborenes: Synthesis, Characterization, and Reactivity Toward Elemental Chalcogens

“…The last 2 decades have seen an increasing interest in the synthesis and reactivity of low oxidation state main group compounds, which are formally isolobal and/or isoelectronic to classical organic molecules, but most often significantly more reactive than the latter. − Doubly Lewis-base-stabilized diborenes of the form B 2 Y 2 L 2 (Y = anionic substituent, L = neutral Lewis base) display a BB double bond and are thereby isoelectronic to alkenes. In 2007, Robinson and co-workers reported the first examples of isolable diborenes, B 2 H 2 (IDip) 2 and B 2 H 2 (IMes) 2 (Figure , IDip = 1,3-bis­(di iso propylphenyl)­imidazol-2-ylidene; IMes = 1,3-bis­(trimethylphenyl)­imidazol-2-ylidene), stabilized by highly sterically demanding and strongly σ-donating N-heterocyclic carbenes (NHCs). , Since then the range of synthetically accessible B 2 Y 2 L 2 diborenes has greatly expanded. − NHC-stabilized diborenes (B 2 Y 2 (NHC) 2 ) are best accessed through the reductive coupling of the corresponding (NHC)­BYX 2 precursors (X = halide) and can be isolated for a wide range of Y substituents, including various aryl (e.g., B 2 Dur 2 (IMe) 2 , Dur = 2,3,5,6-tetramethylphenyl; IMe = 1,3-dimethylimidazol-2-ylidene, Figure ), , furyl and thienyl derivatives, , i Pr, vinyl, and organometallic fragments such as ferrocenediyl and cymantrenyl .…”