Kyle Pearce

Publication date: 15 May 2024

Source: Journal of Organometallic Chemistry, Volume 1012

Author(s): Dat T. Nguyen, Matthew J. Evans, Cameron Jones

Hyping up Europium: Here we report the first examples of molecular europium (II) hydrides, which can be conveniently isolated from the reaction of either symmetrical or unsymmetrical β-diketiminato europium (II) alkyls with 1,4-cyclohexadiene.

Abstract

The bulky β-diketiminate ligand frameworks [BDI^DCHP]⁻ and [BDI^Dipp/Ar]⁻ (BDI=[HC{C(Me)₂N-Dipp/Ar}₂]⁻ (Dipp=2,6-diisopropylphenyl (Dipp); Ar=2,6-dicyclohexylphyenyl (DCHP) or 2,4,6-tricyclohexylphyenyl (TCHP)) have been developed for the kinetic stabilisation of the first europium (II) hydride complexes, [(BDI^DCHP)Eu(μ-H)]₂, [(BDI^Dipp/DCHP)Eu(μ-H)]₂ and [(BDI^Dipp/TCHP)Eu(μ-H)]₂, respectively. These complexes represent the first step beyond the current lanthanide(II) hydrides that are all based on ytterbium. Tuning the steric profile of β-diketiminate ligands from a symmetrical to unsymmetrical disposition, enhanced solubility and stability in the solution–state. This provides the first opportunity to study the structure and bonding of these novel Eu(II) hydride complexes crystallographically, spectroscopically and computationally, with their preliminary reactivity investigated.

A simple and easy to access heterobimetallic system based on Al/Zn combinations is installed. Utilizing Cp*, HMDS and TMP ligands enables regioselective insertions of carbodiimides and ligand substitutions directly at the metal-metal bond. These transformations are accompanied by state-of-the-art quantum chemical calculations.

Abstract

Recent advances on low valent main group metal chemistry have shown the excellent potential of heterobimetallic complexes derived from Al(I) to promote cooperative small molecule activation processes. A signature feature of these complexes is the use of bulky chelating ligands which act as spectators providing kinetic stabilization to their highly reactive Al−M bonds. Here we report the synthesis of novel Al/Zn bimetallics prepared by the selective formal insertion of AlCp* into the Zn−N bond of the utility zinc amides ZnR₂ (R=HMDS, hexamethyldisilazide; or TMP, 2,2,6,6-tetramethylpiperidide). By systematically assessing the reactivity of the new [(R)(Cp*)AlZn(R)] bimetallics towards carbodiimides, structural and mechanistic insights have been gained on their ability to undergo insertion in their Zn−Al bond. Disclosing a ligand effect, when R=TMP, an isomerization process can be induced giving [(TMP)₂AlZn(Cp*)] which displays a special reactivity towards carbodiimides and carbon dioxide involving both its Al−N bonds, leaving its Al−Zn bond untouched.

For over half a century, Mg(anthracene) has been a well-known complex that reacts as a form of “atomic” Mg⁰, however, heavier alkaline-earth metal anthracene complexes are unknown. Reaction of Ba⁰ vapour with an anthracene ligand gave a Ba anthracene complex that crystallizes as a cyclic octamer and reacts as a Ba⁰ synthon.

Abstract

A hydrocarbon-soluble barium anthracene complex was prepared by means of metal vapour synthesis. Reaction of 9,10-bis(trimethylsilyl)anthracene (Anth′′) with barium vapour gave deep purple Ba(Anth′′) which after extraction with diethyl ether crystallised as the cyclic octamer [Ba(Anth′′)⋅Et₂O]₈. Dissolution in benzene or toluene led to replacement of the Et₂O ligand with a softer arene ligand and isolation of Ba(Anth′′)⋅arene. Diffusion ordered spectroscopy (DOSY NMR ) measurements in benzene-d ₆ indicate solution species with a molecular weight that equals a trimeric constitution. Natural population analysis (NPA) assigned charges of +1.70 and −1.70 to Ba and Anth′′, respectively, relating to highly ionic Ba²⁺/Anth′′²⁻ bonding. Preliminary reactivity studies with air, Ph₂C=NPh, or H₂ show that the complex reacts as a Ba⁰ synthon by release of neutral Anth′′. This soluble molecular Ba⁰/Ba^II redox synthon provides new routes for the syntheses of barium complexes under mild conditions.

A non-solvated alkyl-substituted Al(I) anion dimer was synthesized by a reduction of haloalumane precursor using a mechanochemical method. The crystallographic and theoretical analysis revealed its structure and electronic properties. Experimental XPS analysis of the Al(I) anions with reference compounds revealed the lower Al 2p binding energy corresponds to the lower oxidation state of Al species. It should be emphasized that the experimentally obtained XPS binding energies were reproduced by delta SCF calculations and were linearly correlated with NPA charges and 2p orbital energies.

Abstract

A non-solvated alkyl-substituted Al(I) anion dimer was synthesized by a reduction of haloalumane precursor using a mechanochemical method. The crystallographic and theoretical analysis revealed its structure and electronic properties. Experimental XPS analysis of the Al(I) anions with reference compounds revealed the lower Al 2p binding energy corresponds to the lower oxidation state of Al species. It should be emphasized that the experimentally obtained XPS binding energies were reproduced by delta SCF calculations and were linearly correlated with NPA charges and 2p orbital energies.

A ring-expanded NHC, 6-Dipp ((6-Dipp=C{NDippCH₂}₂CH₂, Dipp=2,6-iPr₂C₆H₃)), has been shown to support two acyclic boryls. Reaction of (6-Dipp)CuOtBu with B₂(OMe)₄ provided access to (6-Dipp)CuB(OMe)₂, the first acyclic boryl of copper, which was shown to react similarly to its cyclic cousins. Remarkably, however, it could also be subjected to salt metathesis to access (6-Dipp)CuB(OMe)NMe₂, the second acyclic boryl of copper.

Abstract

Reaction of (6-Dipp)CuOtBu (6-Dipp=C{NDippCH₂}₂CH₂, Dipp=2,6-iPr₂C₆H₃) with B₂(OMe)₄ provided access to (6-Dipp)CuB(OMe)₂ via σ-bond metathesis. (6-Dipp)CuB(OMe)₂ was characterised by NMR spectroscopy and X-ray crystallography and shown to be a monomeric acyclic boryl of copper. (6-Dipp)CuB(OMe)₂ reacted with ethylene and diphenylacetylene to provide insertion compounds into the Cu-B bond which were characterised by NMR spectroscopy in both cases and X-ray crystallography in the latter. It was also competent in the rapid catalytic deoxygenation of CO₂ in the presence of excess B₂(OMe)₄. Alongside π-insertion, (6-Dipp)CuB(OMe)₂ reacted with LiNMe₂ to provide a salt metathesis reaction at boron, giving (6-Dipp)CuB(OMe)NMe₂, a second monomeric acyclic boryl, which also cuproborated diphenylacetylene. Computational interrogation validated these acyclic boryl species to be electronically similar to (6-Dipp)CuBpin.

Publication date: 1 November 2023

Source: Polyhedron, Volume 244

Author(s): Henry T.W. Shere, Michael S. Hill, Mary F. Mahon

Unlocking the metalation potential of Zn(TMP)₂ the addition of KOtBu enables the activation of its amide groups to promote the regioselective zincation of a range of fluoroarenes forming higher order potassium zincates. This methodology can even be extended to non-activated arenes toluene and benzene under mild reaction conditions.

Abstract

Reminiscent of Lochmann-Schlosser superbase recipes, the addition of two molar equivalents of KOtBu to Zn(TMP)₂ (TMP=2,2,6,6-tetramethylpiperidide) transforms this mild zinc bis-amide base to a powerful metalating agent able to perform facile regioselective zincation of a wide range of sensitive fluoroarenes. Structural authentication of the intermediates post Zn−H exchange demonstrates activation of both TMP groups to form a range of higher order bis-aryl potassium zincates, isolable as solids and further functionalized in electrophilic interception reactions. Studies assessing the role of KOtBu reveal that the first equivalent undergoes co-complexation with Zn(TMP)₂, enabling kinetic activation of the amide groups; whereas the second equivalent stabilizes the metalated intermediate preventing ligand redistribution. Showcasing its metalating power, this bimetallic KOtBu/Zn(TMP)₂ partnership, can effect zincation of toluene and benzene at room temperature.

We describe three distinct oligomerization reactions of metal complexes bonded to the cyaphide ligand (CP⁻). Reductive coupling of a gold cyaphido complex was found to afford a species containing a C₂P₂ ⁴⁻ dimer. By contrast, sterically unprotected metal complexes with more polar M−CP (M=Ni, Sc) bonds were found to spontaneously oligomerize giving rise to species with bridging C₂P₂ ²⁻ and C₃P₃ ³⁻ ligands.

Abstract

The cyaphide anion, CP⁻, is shown to undergo three distinct oligomerization reactions in the coordination sphere of metals. Reductive coupling of Au(IDipp)(CP) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) by Sm(Cp*)₂(OEt₂) (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl), was found to afford a tetra-metallic complex containing a 2,3-diphosphabutadiene-1,1,4,4-tetraide fragment. By contrast, non-reductive dimerization of Ni(SIDipp)(Cp)(CP) (SIDipp=1,3-bis(2,6-diisopropylphenyl)-imidazolidin-2-ylidene; Cp=cyclopentadienyl), gives rise to an asymmetric bimetallic complex containing a 1,3-diphosphacyclobutadiene-2,4-diide moiety. Spontaneous trimerization of Sc(Cp*)₂(CP) results in the formation of a trimetallic complex containing a 1,3,5-triphosphabenzene-2,4,6-triide fragment. These transformations show that while cyaphido transition metal complexes can be readily accessed using metathesis reactions, many such species are unstable to further oligomerization processes.

A frustrated Lewis pair (FLP) chelation approach was employed to access low-valent phosphorus centers. The resulting adducts act as P atom sources for phosphinidene (PR) transfer, indium phosphide synthesis, and neutral P₂ transfer to organic substrates.

Abstract

We report phosphinidenes (PR) stabilized by an intramolecular frustrated Lewis pair (FLP) chelate. These adducts include the parent phosphinidene, PH, which is accessed via thermolysis of coordinated HPCO. The reported FLP-PH species acts as a springboard to other phosphorus-containing compounds, such as FLP-adducts of diphosphorus (P₂) and InP₃. Our new adducts participate in thermal- or light-induced phosphinidene elimination (of both PH and PR, R=organic group), transfer P₂ units to an organic substrate, and yield the useful semiconductor InP at only 110 °C from solution.