Rotation-Triggered Transmetalation on a Heterobimetallic Cu/Al N-Phosphine-Oxide-Substituted Imidazolylidene Complex

Abstract

A novel strategy for the preparation of heterobimetallic N-heterocyclic carbene (NHC) complexes is demonstrated using N-phosphine-oxide-substituted imidazolylidenes (PoxIms). In these heterobimetallic Cu/Al complexes, the Cu and Al centers can be either completely separated or brought near each other via the rotation of the N-phosphinoyl group in the PoxIm ligands. Triggered by this rotation, transmetalation to exchange the Cu–OtBu and Al–C6F5 bonds occurs on in situ-generated Cu/Al PoxIm complexes, and the Cu–C6F5 and Al–OtBu bonds are formed in excellent yield. On the basis of the results of mechanistic studies, including the isolation/in situ observation of key complexes and theoretical calculations, a plausible reaction mechanism for an intramolecular transmetalation is proposed to proceed via an activation complex that includes the simultaneous coordination of the phosphinoyl oxygen atom to the Cu as well as the Al centers. Furthermore, the formation of carbon–carbon bonds between Al­(C6F5)3 and allyl bromide mediated/catalyzed by Cu/Al PoxIm complexes is demonstrated. Upon the consecutive transfer of three C6F5 groups from a single molecule of Al­(C6F5)3, allyl pentafluorobenzene derivatives were obtained. The present results demonstrate the role of phosphine oxide in the activation of organoaluminum reagents for the transmetalation between Cu­(I) complexes bearing NHCs as well as the benefit of constructing an intramolecular system based on a heterobimetallic complex to achieve efficient transmetalation by programming the encounter of two organometallic fragments.

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.…”

N‐Phosphine Imide‐Substituted Imidazolylidenes

“…These molecules contain two distinct Lewis bases, i. e. a carbene moiety and a phosphine oxide group, and an electrophilic phosphorus center (Figure 1). [1l,m] Given the multifunctionality of the N ‐phosphinoyl group, PoxIms have been used in frustration revival strategies, [2] for the facile transformation of carbon dioxide into unsymmetrical carbonyl compounds, [3] and the synthesis of mono‐ [4] or hetero‐bimetallic [5] complexes through different coordination modes (e. g. κ ‐ C , κ ‐ O , or κ ‐ C,O ). 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).…”

Complexation-Induced N‒P Axial Chirality in Sm(II) N-Phosphine-Oxide-Substituted Imidazolylidene and Imidazolinylidene Complexes

“…Given that the utility of the multifunctional NHCs reported so far has been limited to their use as multidentate ligands for the complexation of metals, the exploration of an unprecedented application of multifunctional NHCs would significantly advance the development of their chemistry. [7][8][9][10][11] Previously, we have proposed a concept of multifunctional multipurpose carbenes, [12][13][14][15][16][17][18][19][20][21][22] which are carbenes that include functional groups applicable to a variety of purposes beyond solely possessing additional coordination sites. In this context, the N-phosphine-oxidesubstituted imidazolylidene, PoxIm (Figure 1A), and the corresponding imidazolinylidene, SPoxIm, are pioneering examples.…”