Axial Chirality around N–P Bonds Induced by Complexation between E(C₆F₅)₃ (E = B, Al) and an N-Phosphine Oxide-Substituted Imidazolinylidene: A Key Intermediate in the Catalytic Phosphinoylation of CO₂

Abstract

Complexation-induced axial chirality around an N–P bond occurs upon the predominant coordination of the N-phosphinoyl group in the N-phosphine oxide-substituted imidazolinylidene (SPoxIm) to B­(C6F5)3. (R a) and (S a) atropisomers of (κ-O-SPoxIm)­B­(C6F5)3 were observed independently in the single-crystal lattice and the optimized gas-phase structure. Experimental and theoretical studies confirmed that this axial chirality arises from the restricted rotation around the N–P bond, caused by the steric repulsion between the C5–H atoms of the imidazolinylidene ring and the C6F5 rings on the B­(C6F5)3 unit. Conversely, this axial chirality was not certainly observed via the complexation between SPoxIm and Al­(C6F5)3. The carbene carbon atoms in (κ-O-SPoxIm)­E­(C6F5)3 (E = B, Al) remain sufficiently nucleophilic to react with CO2, and the phosphinoylation of CO2 with SPoxIm proceeds far more rapidly in the presence of a catalytic amount of Al­(C6F5)3 than in the absence of Al­(C6F5)3.

N‐Phosphine Imide‐Substituted Imidazolylidenes

“…For example, the complexation of (S)PoxIms with E(C 6 F 5 ) 3 (E=B, Al) furnishes ( κ ‐ O ‐(S)PoxIm)E(C 6 F 5 ) 3 complexes that contain the carbene carbon atoms (Figure 1a). In the case of SPoxIm, axial chirality was induced around the N−P bond in the solid state [4e] . These examples demonstrate that complexation between Lewis acids and the phosphinoyl oxygen atom of (S)PoxIms can afford novel functionalized carbene species.…”

“…Although significant differences are not observed in the bond lengths and angles, ( S a )‐ 3 b and ( R a )‐ 3 b exhibit different C1−N1−P−N3 torsion angles (( S a )‐ 3 b : +161.0(3)°; ( R a )‐ 3 b : −164.9(3)°), demonstrating the presence of axial chirality around their N1−P bonds in the crystalline lattice. The absolute values of these torsion angles are inequivalent, whereas the ( S a ) and ( R a ) atropisomers found in the single‐crystal of ( κ ‐ O ‐SPoxIm)E(C 6 F 5 ) 3 (E=B, Al) exhibited identical structural parameters, including the absolute values of the C−N−P−O torsion angles [4e] . To gain further insight into the axial chirality observed in 3 b , DFT calculations were carried out for both ( S a )‐ 3 b and ( R a )‐ 3 b at the ω B97X‐D/6‐311G(d,p)// ω B97X‐D/6‐31G(d) level of theory (gas phase).…”

A boron-transfer mechanism mediating the thermally induced revival of frustrated carbene–borane pairs from their shelf-stable adducts

“…The molecular structure of (R a )-2aB 2 is shown in Fig. 2b and demonstrates a rare example of complexation-induced N-P axial chirality 29 . As the reaction progressed, 2aB 2 was converted to 3aB 2 and 4a; 2aB 2 was fully consumed within 6 h to afford these compounds in 75% and 25% yield, respectively.…”

“…1) that are comprised of N-phosphine-oxide-substituted imidazolylidenes (PoxIms; 1) and B(C 6 F 5 ) 3 (B 1 ). Here, the revival of the FLP from the CLA is closely controlled by a thermally induced conformational isomerization of the N-phosphinoyl moiety 17,[27][28][29][30] . In 2018, Stephan et al reported a system to control the generation of FLPs from CLAs via a light-induced E/Z isomerization of (C 6 F 5 ) 2 B((p-Tol)S)C = CCH( t Bu) 31 .…”

Room-Temperature Reversible Chemisorption of Carbon Monoxide on Nickel(0) Complexes

“…2A) (25,26). To date, (S)PoxIms have demonstrated various coordination modes toward metals, including coordination by only the carbene atom (-C) (27,28), by only the N-phosphinoyl oxygen atom (-O) (29,30), and by both the carbene and oxygen atoms (-C,O) (31,32); however, dynamic coordination exchange between the -C and -C,O modes remains unknown.…”