Calix[4]pyrrolato gallate: square planar-coordinated gallium(iii) and its metal–ligand cooperative reactivity with CO₂ and alcohols

Abstract

Forcing a priori tetracoordinate atoms into planar configuration represents a promising concept for enhanced reactivity of p-block element-based systems. Herein, the synthesis, characterization, and reactivity of calix[4]pyrrolato gallates, constituting square...

Ligand-enforced geometric constraints and associated reactivity in p-block compounds

“…5c) showing unusually high Lewis acidity for anionic species. 75,76 The origins of the high Lewis acidity have been thoroughly-discussed with referenced to Walsh analysis elsewhere, and are therefore not reproduced here. 77 Highlighting consequences for reactivity, the adjacency of a low-lying vacant p-orbital and heteroatoms or other electron-dense components of an anionic ligand unlocks metal-ligand cooperativity that can be harnessed for catalytic reactivity (Fig.…”

“…5d) such as dehydropolymerization of phosphine-boranes. 75,78,79 Compounds with a group 14 central element Four-coordinate carbon compounds were long believed to only exist in the tetrahedral geometry, as first proposed in 1874 by van't Hoff and Le Bel. 80,81 Since then, several carbon centres featuring unusual geometries have been considered, [82][83][84][85][86] initially as transition state models, 87 and later experimentally by stabilization using transition metals 88 or highly strained cyclic systems.…”

Reversible O–H Bond Activation by Tripodal tris(Nitroxide) Aluminum and Gallium Complexes

“…This is also in agreement with the chemistry reported by the Greb group, who showed enhanced ELC between their calix [4]pyrrolato gallate complex with i-PrOH with preprotonation of the ligand framework. 13 At this point, it is unclear whether one or both pathways are operative, and the specific nature of the proton transfer steps involved in either pathway is not fully elucidated. With these qualifiers, it is tempting to hypothesize that the two complexes 1 and 2 may proceed through different pathways, especially given the difference in rate constants between the complexes.…”

Diverse Cooperative Reactivity at a Square Planar Aluminium Complex and Catalytic Reduction of CO2

“…[11][12][13][14] Examples of structurally constrained tetracoordinate (square planar) group 13 complexes are rare (Figure 1). [15][16][17][18][19] However, those reported remain appreciably Lewis acidic due to their unusual geometry and exhibit MLC reactivity. [20][21][22][23][24][25] We proposed that using an appropriate pincer ligand could induce Lewis acidity at aluminium by structural constraint and the formation of a nucleophilic ligand site to promote MLC reactivity.…”