Superseding β‐Diketiminato Ligands: An Amido Imidazoline‐2‐Imine Ligand Stabilizes the Exhaustive Series of B=X Boranes (X=O, S, Se, Te)

Abstract

Boron reluctantly forms B=X (X=O, S, Se, Te) moieties, which has stimulated the quest for such species in the past few years. Based on the N,N′‐chelating β‐diketiminato ligand (HNacNac), a new amido imidazoline‐2‐imine ligand system (HAmIm) is presented, giving rise to the isolation of an exhaustive series of Lewis acid free, monomeric chalcogen B=X boranes with documented π‐bond character between boron and the chalcogen. The chalcogenoboranes are isoelectronic and isolobal to the respective ketones. The chemical behavior of the oxoborane (B=O) strongly resembles the classical carbonyl reactivity in C=O bonds. The improved stability provided by HAmIm arises from the formation of more‐stable five‐membered boron chelates versus the six‐membered NacNac analogues and from the imidazoline‐2‐imine moiety providing enhanced σ‐ and π‐donation. The HAmIm ligand class may supersede the widely employed NacNac system in certain applications.

Iminoboranes With Parent B=NH Entity: Imino Group Metathesis, Nucleophilic Reactivity and N−N Coupling

“…Compounds 3A and 3B correspond to the dimeric and monomeric lithium bromide adducts of 3 , respectively, and 3C refers to the free monomer. The WBI value of 3C strongly resembles the previously reported value of 1.86 for the B=O double bond in the free oxoborane (AmIm)B=O, [12a] which displays the identical AmIm ligand backbone, see compound 6C in Table S10. The B=NH π‐bond character in compound 3 is also clearly evident from the canonical molecular orbitals (e.g., HOMO‐13, see Table S12), which show distinct π‐bonding interactions between boron and nitrogen.…”

“…In a similar fashion, the reaction of compound 3 with carbon disulfide or an excess of hydrogen sulfide afforded compound 7 , which was reported earlier by us and identified by 1 H and 11 B{ 1 H} NMR spectroscopy [12a] . Again the side products, i. e., ammonia and thiocyanic acid / isothiocyanic acid, were elusive but the reaction with thiobenzophenone afforded benzophenone imine as an isolated material.…”

Amino Imidazolin‐2‐imine Ligands in Magnesium Complexes: Approaches Towards Low‐Valent Mg(I) Species

“…The amido imidazoline‐2‐imine ligand C was recently employed in the preparation of a series of triel(I) carbenoids H including gallium, indium and thallium, which showed ligand donor qualities better than ß ‐diketiminate stabilized analogues [14] . The amido imidazoline‐2‐imine ligand D was employed for the isolation of monomeric boraketones G of type (AmIm)B=E (E=O, S, Se, Te), which provided systematic insight into a complete series with terminal B=E double bonds [15] …”

Base‐Stabilized Neutral Oxoborane and Thioxoborane Supported by a Bis(oxazolinyl)(phenyl)methanide Ligand

“…Even with the Lewis base coordination, however, acid‐free stable neutral oxoboranes have remained elusive until recently. The chemistry of acid‐free oxoborane analogs was opened by the isolation of anionic oxoborane IX by Aldridge in 2019 [23] and a closely related net‐neutral betaine compound X by Trzaskowski and Frank in 2021 [24] . It should also be noted that the latter group has successfully synthesized the whole series of chalcogenoboranes IV , including the first example of telluroxoborane [24] .…”

“…The chemistry of acid‐free oxoborane analogs was opened by the isolation of anionic oxoborane IX by Aldridge in 2019 [23] and a closely related net‐neutral betaine compound X by Trzaskowski and Frank in 2021 [24] . It should also be noted that the latter group has successfully synthesized the whole series of chalcogenoboranes IV , including the first example of telluroxoborane [24] . Recently, Xie and coworkers have reported an NHC‐stabilized oxoborane XI , taking advantage of the sterically bulky and highly σ‐donating carboranyl substituent [25] .…”