Calix[4]pyrrolato Aluminates: The Effect of Ligand Modification on the Reactivity of Square‐Planar Aluminum Anions

Abstract

Structural constraint represents an attractive tool to modify p‐block element properties without the need for unusual oxidation or valence states. The recently reported methyl‐calix[4]pyrrolato aluminate established the effect of forcing a tetrahedral aluminum anion into a square‐planar coordination mode. However, the generality of this structural motif and any consequence of ligand modification remained open. Herein, a systematic ligand screening was launched, and the class of square‐planar aluminum anions was extended by two derivatives that differ in the meso‐substitution at the calix[4]pyrrolato ligand. Strikingly, this modification provoked opposing trends in the preference for a Lewis acidic binding mode with σ‐donors versus the aluminum‐ligand cooperative binding mode with carbonyls. Insights into the origin of these counterintuitive experimental observations were provided by computation and bond analysis. Importantly, this rationale might allow to exploit mode‐selective binding for catalytic rate control.

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

“…All publication charges for this article have been paid for by the Royal Society of Chemistry aluminum compounds (189.3(2) and 188.3(1) pm). 14,15 The average cis-and trans-N-Ga-N angles are 90.0(1) and 90.0(1) , and 178.6(1) and 178.7(1) , respectively. The s 4 value of 0.02 for both gallates indicates essentially perfect square planarity.…”

“…The mean Ga–N bond lengths are 193.8(1) and 195.0(1) pm (the data for [ Me 1] − is always given first), which are larger compared to the analogous aluminum compounds (189.3(2) and 188.3(1) pm). 14,15 The average cis - and trans -N–Ga–N angles are 90.0(1) and 90.0(1)°, and 178.6(1) and 178.7(1)°, respectively. The τ 4 value of 0.02 for both gallates indicates essentially perfect square planarity.…”

“…1 While these so-called van't-Hoff-Le-Bel congurations 2,3 are found in most chemical compounds, precise ligand design allowed unique exceptions to this paradigm. [4][5][6][7][8][9][10][11][12][13] Most recent additions are the square planar anti-van't-Hoff-Le-Bel cases for aluminum 14,15 and silicon 16 by using the macrocyclic calix [4]pyrrolato ligand (Fig. 1A).…”

BAl4Mg−/0/+: Global Minima with a Planar Tetracoordinate or Hypercoordinate Boron Atom

“…From the time that the concept of planar tetracoordinate carbon (ptC) emerged [1,2], it was extended not only to its group elements (Si, Ge, Sn, etc.) [3][4][5][6][7][8][9][10] but also to other elements such as B [11][12][13][14][15][16][17], Al [18,19], N [20][21][22], P [23], O [24], and lately even to the F atom [25]. There are two main reasons why experimentalists [5,6,[26][27][28][29][30][31][32][33] and theoreticians [2,[34][35][36][37][38][39][40][41][42][43] have put a great deal of effort into studying these special class of molecules: (i) ptC is a fundamental deviation from the conventional ideas of tetrahedral tetracoordinate carbon [44,…”

Calix[4]pyrrolato Aluminate Catalyzes the Dehydrocoupling of Phenylphosphine Borane to High Molar Weight Polymers

“…Herein, we describe the application of calix [4]pyrrolato aluminates, [17] well-known for metal-ligand cooperativity, [17b, 18] as the first transition metal-free catalysts for the synthesis of high molar mass polyphosphinoboranes (Scheme 1C).…”