X-Type Aluminyl Ligands for Transition-Metal Catalysis

Abstract

Transition-metal complexes that bear group-13 X-type metalloligands have attracted considerable interest on account of their strong σ-donicity, which can dramatically tune the reactivity of transition-metal catalysts. Among the group-13 X-type metalloligands, X-type aluminyl ligands are especially interesting due to the low electronegativity and strong Lewis acidity of the Al atom. However, transition-metal complexes that bear X-type aluminyl ligands had until recently remained elusive. In this perspective, we describe the reactivity of transition-metal complexes that carry a well-designed X-type PAlP pincer-ligand and their characteristic features, i.e., strong σ-donicity, trans-influence, reverse bond polarization, and Lewis acidity. These properties enable various catalytic transformations, including transfer dehydrogenation, highly efficient CO2 reduction, site-selective C–H-bond functionalization, and cooperative C–F- and C–O-bond functionalization, which are challenging to achieve using conventional catalyst systems.

Reactivity of Unsupported Transition Metal-Aluminyl Complexes: A Nucleophilic TM-Al Bond

“…). − Indeed, the TM-aluminyl complexes have shown their potential in small-molecule activation in recent studies, as exemplified by their insertion reactions with heteroallenes like carbon dioxide (CO 2 ) ( vide infra ). Because of the possible implication of TM-aluminyl complexes in catalysis, they have recently attracted increasing attention in the aspects of synthesis, reactivity, and electronic structure studies. − …”

“…Among those TM-aluminyl complexes reported to react with heteroallenes, there are simple structures with a clear TM–Al σ bond ,,− and more sophisticated structures with extensive bridging across the TM center and the aluminyl unit. − The focus of this study will be on the understanding of reactivity for those simpler cases with an unsupported TM–Al bond, in which there should be less influence from the other coordinations and it would allow us to pinpoint the source of reactivity.…”

Diverse reactivity of an iron–aluminium complex with substituted pyridines

“…21 This provides a further example how heterobimetallic cooperativity can affect the reactivity or selectivity of a main group species. 22–24…”

“…21 This provides a further example how heterobimetallic cooperativity can affect the reactivity or selectivity of a main group species. [22][23][24] Further variation of the substrate revealed that 1 can react selectively at sp 3 C-H bonds of pyridines in the presence of sp 2 C-H bonds. Hence, addition of 2-methylpyridine to 1 resulted in deprotonation of the CH 3 group to afford 7 in 495% NMR yield (Fig.…”

Diverse Reactivity of an Iron–Aluminium Complex with Substituted Pyridines

“…21 This provides a further example how heterobimetallic cooperativity can affect the reactivity or selectivity of a main group species. [22][23][24] Further variation of the substrate revealed that 1 can react selectively at sp 3 C-H bonds of pyridines in the presence of sp 2 C-H bonds. Hence, addition of 2-methylpyridine to 1 resulted in deprotonation of the CH3 group to afford 7 in >95 % NMR yield (Figure 3).…”