Development and Applications of Sterically Demanding Ligands in Main Group Chemistry

A special issue of Inorganics (ISSN 2304-6740). This special issue belongs to the section "Coordination Chemistry".

Deadline for manuscript submissions: 31 March 2025 | Viewed by 3574

Special Issue Editor


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Guest Editor
EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews KY16 9ST, UK
Interests: molecular main group of compounds; low-oxidation state complexes; metal–metal-bonded complexes; main group of metal hydride complexes; main group of organometallics; sterically demanding ligands

Special Issue Information

Dear Colleagues,

Many recent advances in main group chemistry have been achieved with compounds bearing highly sterically demanding ligand systems. This has led, for example, to the discovery of complexes with elements in low coordination and novel bonding modes, rare oxidation states, and compounds with unique properties. Many of these compounds have been capable of activating highly inert small molecules under mild conditions, leading to the discovery of novel stoichiometric and catalytic reactivity. The sterically demanding ligands in these complexes can shape compound geometries and properties, facilitate, or prevent certain reaction pathways, and thus enable new forms of chemistry with main group elements.

These endeavours often started with exploratory fundamental studies on sterically demanding ligand systems at main group element centres, leading to a wide range of both broadly anticipated findings and highly surprising discoveries. Many efforts have been made in synthesising, characterising, and studying these compound classes, helping to shape our understanding of the fine balance of steric and electronic effects in these compounds, which is still developing. The synthesis of new sterically demanding ligand systems, their connection to main group fragments, and the further transformations of their complexes can lead to new challenges; however, because of the significant impact of the ligand bulk, in some instances, minor differences in ligand architecture have led to significantly different reaction outcomes and this field still holds many surprises and opportunities for main group chemistry.

In this Special Issue, we welcome contributions to this field that shed light on new findings in main group chemistry with sterically demanding ligand systems.

Dr. Andreas Stasch
Guest Editor

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Keywords

  • sterically demanding ligands
  • ligand design and synthesis
  • s- and p-block complexes
  • low-coordination modes
  • main group synthesis and catalysis

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Published Papers (4 papers)

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Research

24 pages, 5030 KiB  
Article
EtIDip (EtIPr)—Synthesis, Characterisation and Reactivity of a Robust, Backbone-Modified N-Heterocyclic Carbene and Group 13 Element Complexes
by Huanhuan Dong, Albert Martinez-Segura, Riley W. Kelehan, Connor Bourne, Aidan P. McKay, Alexandra M. Z. Slawin, David B. Cordes and Andreas Stasch
Inorganics 2025, 13(1), 27; https://doi.org/10.3390/inorganics13010027 - 17 Jan 2025
Viewed by 531
Abstract
We report the synthesis, characterisation and reactivity of the stable imidazol-2-ylidene EtIDip (EtIPr), {EtCN(Dip)}2C:, Dip = 2,6-iPr2C6H3, as a chemically robust alternative to IDip (IPr), {HCN(Dip)}2C:. The N-heterocyclic [...] Read more.
We report the synthesis, characterisation and reactivity of the stable imidazol-2-ylidene EtIDip (EtIPr), {EtCN(Dip)}2C:, Dip = 2,6-iPr2C6H3, as a chemically robust alternative to IDip (IPr), {HCN(Dip)}2C:. The N-heterocyclic carbene EtIDip could be further converted to the oxidised species [EtIDipCl]Cl, EtIDipF2, EtIDipO, and EtIDipSe, and the group 13 element complexes EtIDipEX3, with E = B, X = Br; E = Al, X = I; E = Ga, X = I; E = Al, X = H. The properties of the EtIDip and IDip ligands are compared and the molecular structures of (DipNCEt)2, [EtIDipH]Cl, [EtIDipH]I, EtIDip, [EtIDipCl]Cl, EtIDipF2, EtIDipO, EtIDipBBr3, EtIDipAlI3, EtIDipGaI3, and EtIDipAlH3 have been determined. Full article
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12 pages, 3093 KiB  
Article
Tetrazenyl-, Imido-, and Azidoaluminate Derivatives of a Sterically Demanding Bis-Silazide Ligand
by Han-Ying Liu, Ryan J. Schwamm, Jakub Kenar, Mary F. Mahon and Michael S. Hill
Inorganics 2025, 13(1), 25; https://doi.org/10.3390/inorganics13010025 - 16 Jan 2025
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Abstract
The potassium alumanyl [{SiNDipp}AlK]2 (SiNDipp = {CH2SiMe2NDipp}2; Dipp = 2,6-i-Pr2C6H3) reacts with organic azides via reductive N2 elimination. With the less sterically encumbered azides [...] Read more.
The potassium alumanyl [{SiNDipp}AlK]2 (SiNDipp = {CH2SiMe2NDipp}2; Dipp = 2,6-i-Pr2C6H3) reacts with organic azides via reductive N2 elimination. With the less sterically encumbered azides PhN3 and C10H15N3 (1-azidoadamantane), the putative initially formed aluminium imide undergoes facile [2 + 3] cycloaddition to provide the tetrazenylaluminates [{SiNDipp}Al-κ2-N,N′-({N(R)}2N2)]K (R = Ph, C10H15). In contrast, each Al(I) centre of [{SiNDipp}AlK]2 only reacts with a single equivalent of 2,4,6-Me3C6H2N3 to provide the imidoaluminate [{SiNDipp}AlN(2,4,6-Me3C6H2)(K∙C6H6)], which crystallises as a monomer and displays a short Al-N distance of 1.7040(13) Å. Attempts to synthesise the azide [{SiNDipp}AlN3] by reaction of [{SiNDipp}AlI] with an excess of KN3 resulted in exclusive formation of the bis(azido)aluminate [{SiNDipp}Al(N3)2K], which crystallises as an infinite 1-dimensional polymer propagated by μ-(1,3)-N3 bridging interactions between the potassium cations and azide anions. Although the THF-adducted azide [{SiNDipp}AlN3(THF)] may be synthesised and characterised by more stringent control of the reaction stoichiometry, the synthetic viability of this route remains compromised by competitive generation of [{SiNDipp}Al(N3)2K]. Full article
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10 pages, 6891 KiB  
Article
Oxidative Addition to Group 1 (K, Rb, Cs) Alumanyl Anions as a Route to o-Carboranyl (hydrido)aluminates
by Han-Ying Liu, Kyle G. Pearce, Michael S. Hill and Mary F. Mahon
Inorganics 2024, 12(12), 309; https://doi.org/10.3390/inorganics12120309 - 27 Nov 2024
Viewed by 889
Abstract
The kinetic stability provided by the sterically demanding {SiNDipp}2− dianion (SiNDipp = {CH2SiMe2NDipp}2; Dipp = 2,6-i-Pr2C6H3) is intrinsic to the isolation of not only the [...] Read more.
The kinetic stability provided by the sterically demanding {SiNDipp}2− dianion (SiNDipp = {CH2SiMe2NDipp}2; Dipp = 2,6-i-Pr2C6H3) is intrinsic to the isolation of not only the group 1 alumanyl reagents ([{SiNDipp}AlM]2; M = K, Rb, Cs) but also facilitates the completely selective oxidative addition of a C-H bond of 1,2-C2B10H12 to the aluminium centre. In each case, the resultant compounds comprise a four-coordinate o-carboranyl (hydrido)aluminate anion, [(SiNDipp)Al(H)(1,2-C2B10H11)], in which the carboranyl cage is bonded to aluminium by an Al-C σ bond. Although the anions further assemble as extended network structures based on Al-H∙∙∙M, B-H∙∙∙M, and C-H∙∙∙M interactions, each structure is unique due to the significant variation in M+ ionic radius as group 1 is descended. The potassium derivative crystallises as a one-dimensional polymer, its rubidium analogue is a dimer due to the polyhapto-sequestration of a molecule of benzene solvent within the alkali metal coordination sphere, and the caesium species is a two-dimensional assembly of hexameric aggregates. Full article
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14 pages, 2218 KiB  
Article
Synthesis and Characterization of Extremely Bulky Aminopyridinate Ligands and a Series of Their Groups 1 and 2 Metal Complexes
by Arif M. Earsad, Albert Paparo, Matthew J. Evans and Cameron Jones
Inorganics 2024, 12(10), 270; https://doi.org/10.3390/inorganics12100270 - 15 Oct 2024
Cited by 1 | Viewed by 1307
Abstract
High-yielding synthetic routes to five new extremely bulky aminopyridine pro-ligands were developed, viz. (C5H3N-6-Ar1)N(H)Ar2-2; Ar1 = Trip, Ar2 = TCHP (HAmPy1), Ar* (HAmPy2) or Ar (HAmPy3); [...] Read more.
High-yielding synthetic routes to five new extremely bulky aminopyridine pro-ligands were developed, viz. (C5H3N-6-Ar1)N(H)Ar2-2; Ar1 = Trip, Ar2 = TCHP (HAmPy1), Ar* (HAmPy2) or Ar (HAmPy3); Ar1 = TCHP, Ar2 = Ar* (HAmPy4) or Ar (HAmPy5) (Trip = 2,4,6-triisopropylphenyl, TCHP = 2,4,6-tricyclohexylphenyl, Ar* = C6H2(CHPh2)2Me-2,6,4, Ar = C6H2(CHPh2)2Pri-2,6,4. Four of these were deprotonated with LiBun in diethyl ether to give lithium aminopyridinate complexes which were dimeric for the least bulky ligand, [{Li(AmPy1)}2] or monomeric for the bulkier aminopyridinates, i.e., in [Li(AmPy2−4)(OEt2)]. One aminopyridine was deprotonated with MeMgI to give monomeric [Mg(AmPy3)I(OEt2)2]. When treated with sodium or potassium mirrors or 5% w/w Na/NaCl, over-reduction occurred, leading to the alkali metal aminopyridinates, [M(AmPy3)(η6-toluene)] (M = Na or K) or [{Na(AmPy3)}]. An attempted reduction of [Mg(AmPy3)I(OEt2)2] with a dimagnesium(I) compound led only to partial loss of diethyl ether and the formation of [(AmPy3)Mg(μ-I)2Mg(AmPy3)(OEt2)]. All prepared complexes have potential as ligand transfer reagents in salt metathesis reactions with metal halide complexes. Full article
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