Structural and Electronic Properties of Boranes Containing Boron‐Chalcogen Multiple Bonds and Stabilized by Amido Imidazoline‐2‐imine Ligands

Abstract

The stabilization of elusive monomeric species containing multiple boron‐chalcogen bonds has motivated the investigation of sophisticated ligand systems in the past few years. Recently, a series of neutral, Lewis acid‐free chalcogenboranes were prepared by incorporation of an amido imidazoline‐2‐imine as the supporting ligand (Frank et al., Angew. Chem. Int. Ed. 2021, 60, 4633), resulting in well‐defined molecular entities with pronounced multiple bond character, B=X (X=O, S, Se, Te). In view of the potential use of N‐heterocyclic boranes (NHB=X) as ligands in catalysis and fine chemistry, we evaluated in this work the bonding properties of the new B=X compounds based on a π‐backdonation model. The electronic properties of systems in question were modulated via systematic modifications of the NHB ring with respect to ligand variation, saturation, size, and heteroatom substitutions. Investigations into the B=X bond length and order, calculated by means of density functional theory methods, reveal enhanced B=X bonding properties for NHB rings with high electron delocalization in the NHB ring and bearing electron‐withdrawing substituents; a fact that was also confirmed by computational assessment of electron interactions of the B=X species with a dicarbonyl manganese complex. We expect that the analysis will contribute to the rational optimization of existing ligands as well as the development of new moieties, which would further allow for exploration of new boron chemistry.

Electrophilicity of Hoveyda‐Grubbs Olefin Metathesis Catalysts as the Driving Force that Controls Initiation Rates

“…The Ru=C length reduction is also reflected in a steady and linear enlargement of NHCÀ Ru distance (R 2 = 0.91). Although variations in a range of 0.02 Å are small in accordance with the rigidity of HG catalysts (standard deviation, SD < 0.01 Å), and uncertainty can be argued, [42] we were able to observe the effect of the catalyst substituent on k D , which is discussed later.…”

“…We previously obtained similar results in N-heterocyclic boranes. [42] It is also interesting to note that Δμ is positive for NO 2 and ketone substituents, which means that a higher amount of energy is released when the number of electrons changes in the corresponding complexes 1 (see Table 2). That is, catalysts 1(EWG) are more reactive due to more accessible LUMOs (reduced μ) and reduced HOMO-LUMO gaps.…”

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

“…However, the experimental trend of BÀ O bond lengths and strength of BÀ O stretching among X, 3, and XI are contradictory (rows 2 and 3 in Table 1), possibly due to the difference in the measurement methods. Since Martínez and Trzaskowski reported a good correlation between BÀ O bond length and BÀ O bond strength in their computational analysis of various chalcogenoboranes, [41] we also theoretically investigated the nature of BÀ O double bonds at the B3LYP/ def2-TZVP level of theory. Wiberg bond indices reproduced the order of experimental BÀ O bond strength based on their bond lengths (See rows 2 and 4 in Table 1).…”

Iron(I) and Iron(II) Amido-imidazolin-2-imine Complexes as Catalysts for H/D Exchange in Hydrosilanes

“…In light of these findings, we sought to synthesize related iron complexes containing the AmIm ligand, − which has been shown to be a stronger and more electron-rich monoanionic N,N′ -donor ligand compared to β-diketiminates, due to the strong π-electron donating ability of both the amido and the imidazolin-2-imine moieties. , Hence, in this work, we present the iron­(I) and iron­(II) complexes 5 and 7 supported by the AmIm ligand, which allow a systematic comparison with Webster’s iron­(II) catalyst 1 and with our Co­(I) catalyst 2 (Chart ). , The compounds 5 and 7 were used as precatalysts in H/D exchange reactions with D 2 in hydrosilanes.…”