Intramolecularly Coordinated 2‐Iminomethylphenyltellurium Compounds

Abstract

Procedures for the synthesis of 2-(tBuNCH)-C 6 H 4 Te(S 2 CNEt 2 ) (1a), 2-(2′,6′-iPr 2 C 6 H 3 NCH)C 6 H 4 Te(S 2 CNEt 2 ) (1b), [2-(tBuNCH)C 6 H 4 ] 2 Te (2a), 2-(tBuNCH)C 6 H 4 TeCl (3a), and 2-(tBuNCH)C 6 H 4 TeCl 3 (4a) have been developed. Compounds 1a-4a possess 2-iminomethylphenyl groups that provide intramolecular N donation to the Te atoms, which was investigated by multinuclear NMR spectroscopy and X-ray crystallography. The Te-N bond lengths increase in the order 3a [2.203 (2) Å] < 4a [2.286(1) Å] < 1b [2.337(2) Å] < 1a [2.407(2) Å] < 2a [a] 3435 Scheme 1. Tellurium compounds stabilized by intramolecular N(sp 3 ) donation (top row) and N(sp 2 ) donation (bottom row). Full PaperScheme 2. General route for the synthesis of 2-iminomethylphenyltellurium compounds reported in the literature. analyzed through DFT calculations and real-space bonding indicators (RSBI), which are derived from the computed electron and pair densities. Topological dissection of the electron density (ED) according to the atoms-in-molecules (AIM) space-partitioning scheme [88] provides a bond-path motif that resembles the molecular structure as well as details of atomic properties such as charges and volumes. Analysis of the reduced density gradient, s(r) = [1/2(3π 2 ) 1/3 ]|∇ρ|/ρ 4/3 , according to the recently introduced noncovalent interactions (NCI) index [89] affords noncovalent bonding aspects. Notably, the assignment of different contact types, including steric/repulsive (λ 2 > 0), van der Waals like (λ 2 ≈ 0), and attractive (λ 2 < 0) interactions is facilitated by mapping the product of the ED and the sign of the second eigenvalue of the Hessian [sign(λ 2 )ρ] on the isosurfaces of s(r). Finally, topological dissection of the pair density according to the electron localizability indicator (ELI-D) [90] provides core, bonding, and lone-pair basins, which are especially valuable for the analysis of covalent (including dative) bonds. ELI-D isosurfaces (localization domain representations of the basins) and NCI isosurfaces show a complementary spatial distribution, [91] which suggests spatial separation of covalent and noncovalent bonding aspects, which has been a matter of recent debate. [92] The combination of AIM, NCI, and ELI-D thus allows the monitoring of minute electronic changes in the Te-N interaction, which is dominated by covalent bonding aspects for short Te-N distances and ionic bonding aspects for longer Te-N distances. These calculations extend previous computational studies on intramolecularly coordinated N-donor tellurium compounds by us [93] and others. [94,95] Scheme 3. Synthesis of 1a-4a and 1b.

The Aromatic 2-Iminomethylphenyltellurenyl Cation. A Lewis Superacid Despite the Intramolecularly Coordinating N-Donor Ligand

“…2.1129(10), 2.0755(15), and 2.051(4) Å for 1–3 , respectively, and these values correspond to or are even shorter than a value for a single bond [∑ cov (Te–N) = 2.07 Å], indicating very strong mutual interaction. This value is shorter than those found either in the starting material 2-( tert -butyliminomethyl)­phenyltellurenyl chloride [2.203(2) Å] or in known examples of the tellurenyl cations stabilized with tridentate N,C,N-pincer ligands reported by Singh et al [in the range of 2.210(7)–2.287(2) Å]. Furthermore, the C1–N1 bonds in 1–3 are elongated in comparison with the typical CN bond [cf.…”

“…Compounds 1–3 were obtained by a chloride abstraction starting from 2-( tert -butyliminomethyl)­phenyltellurenyl chloride, 2-( t BuNCH)­C 6 H 4 TeCl, using silver salts of weakly coordinating anions AgX {X = O 3 SCF 3 , SbF 6 , or Al­[OC­(CF 3 ) 3 ] 4 (Scheme )}. All compounds were isolated as yellow to orange crystalline solids in nearly quantitative yields that are only almost insoluble in nonpolar solvents but exhibit good solubility in dichloromethane and THF.…”

“…2-(tBuNCH)C 6 H 4 TeCl was synthesized according to a published procedure. 16 Silver trifluoro m e t h a n e s u l f o n a t e ( A g O 3 S C F 3 , ≥ 9 9 % ) a n d s i l v e r hexafluoroantimonate(V) (AgSbF 6 , 98%) were obtained from Sigma-Aldrich. Silver tetrakis(perfluoro-tert-butoxy)aluminate (Ag-{Al[OC(CF 3 ) 3 ] 4 }, 99%) was obtained from IOLITEC GmbH.…”

Lewis Superacidic Tellurenyl Cation‐Induced Electrophilic Activation of an Inert Carborane

“…[3] These ion pairs , which is known as robust entity with a very low reactivity. [4] However, the salt metathesis reaction of 2-(tBuNCH)C 6 H 4 TeCl (II) [5] with Ag[CB 11 H 12 ] [6] provided again a contact ion pair [2-(tBuNCH)C 6 H 4 Te][CB 11 H 12 ] (1), which was isolated as yellow crystals in 99 % yield (Scheme 1, Figure 2). [7] In the solid state, the dative N!Te bond (2.088(2) Å) of 1 is shorter than that of (tBuNCH)C…”

“…In an effort to obtain an essentially isolated [2‐( t BuNCH)C 6 H 4 Te] + ( I ) cation, we turned our attention to an alternative WCA, namely, the closo ‐carborane anion [CB 11 H 12 ] − , which is known as robust entity with a very low reactivity. [4] However, the salt metathesis reaction of 2‐( t BuNCH)C 6 H 4 TeCl ( II ) [5] with Ag[CB 11 H 12 ] [6] provided again a contact ion pair [2‐( t BuNCH)C 6 H 4 Te][CB 11 H 12 ] ( 1 ), which was isolated as yellow crystals in 99 % yield (Scheme 1 , Figure 2 ). [7] In the solid state, the dative N→Te bond (2.088(2) Å) of 1 is shorter than that of ( t BuNCH)C 6 H 4 Te][O 3 SCF 3 ] (2.113(1) Å), but longer than those of ( t BuNCH)C 6 H 4 Te][SbF 6 ] (2.076(2) Å) and ( t BuNCH)C 6 H 4 Te][Al{OC(CF 3 ) 3 } 4 ] (2.051(4) Å).…”