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Calcium fluoride is the ultimate source of all fluorochemicals. Current synthetic approaches rely on the use of HF, generated from naturally occurring fluorspar and sulfuric acid. Methods for constructing E-F bonds directly from CaF 2 have long been frustrated by its high lattice energy, low solubility and impaired fluoride ion nucleophilicity. Little fundamental understanding of the reactivity of Ca-F moieties is available to guide methodology development; well-defined molecular species containing Ca-F bonds are extremely rare, and existing examples are strongly aggregated and evidence no nucleophilic fluoride delivery. Here, by contrast, we show that by targeting anionic systems of the type [L n (X) 2 CaF] - , monomeric calcium fluoride complexes containing single Ca-F bonds can be synthesized, including via routes involving fluoride abstraction from existing C-F bonds. Comparative structural and spectroscopic studies of mono- and dinuclear systems allow us to define structure-activity relationships for E-F bond formation from molecular calcium fluorides., (© 2024. The Author(s).)

Bimetallic compounds containing direct metal-group 13 element bonds have been shown to display unprecedented patterns of cooperative reactivity towards small molecules, which can be influenced by the identity of the group 13 element. In this context, we present here a systematic appraisal of group 13 metallo-ligands of the type [(NON)E] - (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) for E=Al, Ga and In, through a comparison of structural and spectroscopic parameters associated with the trans L or X ligands in linear d 10 complexes of the types LM{E(NON)} and XM'{E(NON)}. These studies are facilitated by convenient syntheses (from the In(I) precursor, InCp) of the potassium indyl species [{K(NON)In}⋅KCp] n (1) and [(18-crown-6) 2 K 2 Cp] [(NON)In] (1'), and lead to the first structural characterisation of Ag-In and Hg-E (E=Al, In) covalent bonds. The resulting structural, spectroscopic and quantum chemical probes of Ag/Hg complexes are consistent with markedly stronger σ-donor capabilities of the aluminyl ligand, [(NON)Al] - , over its gallium and indium counterparts., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The homoleptic magnesium bis(aluminyl) compound Mg[Al(NON)] 2 (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) can be accessed from K 2 [Al(NON)] 2 and MgI 2 and shown to possess a non-linear geometry (∠Al-Mg-Al=164.8(1)°) primarily due to the influence of dispersion interactions. This compound acts a four-electron reservoir in the reductive de-fluorination of SF 6 , and reacts thermally with polar substrates such as MeI via nucleophilic attack through aluminium, consistent with the QT-AIM charges calculated for the metal centres, and a formal description as a Al(I)-Mg(II)-Al(I) trimetallic. On the other hand, under photolytic activation, the reaction with 1,5-cyclooctadiene leads to the stereo-selective generation of transannular cycloaddition products consistent with radical based chemistry, emphasizing the covalent nature of the Mg-Al bonds and a description as a Al(II)-Mg(0)-Al(II) synthon. Consistently, photolysis of Mg[Al(NON)] 2 in hexane in the absence of COD generates [Al(NON)] 2 together with magnesium metal., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

While the nucleophilic addition of ammonia to ketones is an archetypal reaction in classical organic chemistry, the reactivity of heavier group 14 carbonyl analogues (R 2 E=O; E=Si, Ge, Sn, or Pb) with NH 3 remains sparsely investigated, primarily due to the synthetic difficulties in accessing heavier ketone congeners. Herein, we present a room-temperature stable boryl-substituted amidinato-silanone {(HCDippN) 2 B}{PhC(tBuN) 2 }Si=O (Dipp=2,6-iPr 2 C 6 H 3 ) (together with its germanone analogue), formed from the corresponding silylene under a N 2 O atmosphere. This system reacts cleanly with ammonia in 1,2-fashion to give an isolable sila-hemiaminal complex {(HCDippN) 2 B}{PhC(tBuN) 2 }Si(OH)(NH 2 ). Quantum chemical calculations reveal that the formation of this sila-hemiaminal is crucially dependent on the nature of the ancillary ligand scaffold. It is facilitated thermodynamically by the hemi-lability of the amidinate ligand (which allows for the formation of an energetically critical intramolecular N⋅⋅⋅HO hydrogen bond within the product) and is enabled mech-anistically by a process in which the silanone initially acts in umpolung fashion as a base (rather than an acid), due to the strongly electron-releasing and sterically bulky nature of the ancillary boryl ligand., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A tetraboryl digermene synthesized by the reaction between a dianionic digermanide nucleophile and a boron halide electrophile is dimeric both in the solid state and in hydrocarbon solution. It features both a planar 'alkene-like' geometry for the Ge 2 B 4 core, and an exceptionally short GeGe double bond. These structural features are consistent with the known electronic properties of the boryl group, and with lowest energy ( in silico ) fragmentation into two triplet bis(boryl)germylene fragments.

We report on a comprehensive reactivity study starting from [AuF 3 (SIMes)] to synthesize different motifs of monomeric gold(III) fluorides. A plethora of different ligands has been introduced in a mono-substitution yielding trans-[AuF 2 X(SIMes)] including alkynido, cyanido, azido, and a set of perfluoroalkoxido complexes. The latter were better accomplished via use of perfluorinated carbonyl-bearing molecules, which is unprecedented in gold chemistry. In case of the cyanide and azide, triple substitution gave rise to the corresponding [AuX 3 (SIMes)] complexes. Comparison of the chemical shift of the carbene carbon atom in the 13 C{ 1 H} NMR spectrum, the calculated SIMes affinity and the Au-C bond length in the solid state with related literature-known complexes yields a classification of trans-influences for a variety of ligands attached to the gold center. Therein, the mixed fluorido perfluoroalkoxido complexes have a similar SIMes affinity to AuF 3 with a very low Gibbs energy of formation when using the perfluoro carbonyl route., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

All fluorochemicals-including elemental fluorine and nucleophilic, electrophilic, and radical fluorinating reagents-are prepared from hydrogen fluoride (HF). This highly toxic and corrosive gas is produced by the reaction of acid-grade fluorspar (>97% CaF 2 ) with sulfuric acid under harsh conditions. The use of fluorspar to produce fluorochemicals via a process that bypasses HF is highly desirable but remains an unsolved problem because of the prohibitive insolubility of CaF 2 . Inspired by calcium phosphate biomineralization, we herein disclose a protocol of treating acid-grade fluorspar with dipotassium hydrogen phosphate (K 2 HPO 4 ) under mechanochemical conditions. The process affords a solid composed of crystalline K 3 (HPO 4 )F and K 2- x Ca y (PO 3 F) a (PO 4 ) b , which is found suitable for forging sulfur-fluorine and carbon-fluorine bonds.

The reduction of the boryl-substituted Sn II bromide {(HCDippN) 2 B}Sn(IPrMe)Br with 1.5 equivalents of potassium graphite leads to the generation of the cyclic tetratin tetraboryl system K 2 [Sn 4 {B(NDippCH) 2 } 4 ], a homo-metallic heavier analogue of the cyclobutadiene dianion. This system is non-aromatic as determined by Nucleus Independent Chemical Shift Calculations (NICS(0)=-0.28, NICS(1)=-3.17), with the primary contributing resonance structures shown by Natural Resonance Theory (NRT) to involve a Sn=Sn double bond and 1,2-localized negative charges. Abstraction of the K + cations or oxidation leads to contraction or cleavage of the Sn 4 unit, respectively, while protonation generates the neutral dihydride 1,2-Sn 4 {B(NDippCH) 2 } 4 H 2 (a heavier homologue of cyclobutene) in a manner consistent with the predicted charge distribution in the [Sn 4 {B(NDippCH) 2 } 4 ] 2- dianion., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

A new synthetic access to the Lewis acid [Au(OTeF 5 ) 3 ] and the preparation of the related, unprecedented anion [Au(OTeF 5 ) 4 ] - with inorganic or organic cations starting from commercially available and easy-to-handle gold chlorides are presented. In this first extensive study of the Lewis acidity of a transition-metal teflate complex by using different experimental and quantum chemical methods, [Au(OTeF 5 ) 3 ] was classified as a Lewis superacid. The solid-state structure of the triphenylphosphine oxide adduct [Au(OPPh 3 )(OTeF 5 ) 3 ] was determined, representing the first structural characterization of an adduct of this highly reactive [Au(OTeF 5 ) 3 ]. Therein, the coordination environment around the gold center slightly deviates from the typical square planar geometry. The [Au(OTeF 5 ) 4 ] - anion shows a similar coordination motif., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The reactions of anionic aluminium or gallium nucleophiles {K[E(NON)]} 2 (E = Al, 1 ; Ga, 2 ; NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di tert -butyl-9,9-dimethylxanthene) with beryllocene (BeCp 2 ) led to the displacement of one cyclopentadienyl ligand at beryllium and the formation of compounds containing Be-Al or Be-Ga bonds (NON)EBeCp (E = Al, 3 ; Ga, 4 ). The Be-Al bond in the beryllium-aluminyl complex [2.310(4) Å] is much shorter than that found in the small number of previous examples [2.368(2) to 2.432(6) Å], and quantum chemical calculations suggest the existence of a non-nuclear attractor (NNA) for the Be-Al interaction. This represents the first example of a NNA for a heteroatomic interaction in an isolated molecular complex. As a result of this unusual electronic structure and the similarity in the Pauling electronegativities of beryllium and aluminium, the charge at the beryllium center (+1.39) in 3 is calculated to be less positive than that of the aluminium center (+1.88). This calculated charge distribution suggests the possibility for nucleophilic behavior at beryllium and correlates with the observed reactivity of the beryllium-aluminyl complex with N,N' -diisopropylcarbodiimide─the electrophilic carbon center of the carbodiimide undergoes nucleophilic attack by beryllium, thereby yielding a beryllium-diaminocarbene complex.

Boryltin compounds featuring the metal in the+1 or 0 oxidation states can be synthesized from the carbene-stabilized tin(II) bromide (boryl)Sn(NHC)Br (boryl={B(NDippCH) 2 }; NHC=C{(N i PrCMe) 2 }) by the use of strong reducing agents. The formation of the mono-carbene stabilized distannyne and donor-free distannide systems (boryl)SnSn(IPrMe)(boryl) (2) and K 2 [Sn 2 (boryl) 2 ] (3), using Mg(I) and K reducing agents mirrors related germanium chemistry. In contrast to their lighter congeners, however, systems of the type [Sn(boryl)] n are unstable with respect to disproportionation. Carbene abstraction from 2 using BPh 3 , and two-electron oxidation of 3 both result in the formation of a 2 : 1 mixture of the Sn(II) compound Sn(boryl) 2 , and the hexatin cluster, Sn 6 (boryl) 4 (4). A viable mechanism for this rearrangement is shown by quantum chemical studies to involve a vinylidene intermediate (analogous to the isolable germanium compound, (boryl) 2 Ge=Ge), which undergoes facile atom transfer to generate Sn(boryl) 2 and trinuclear [Sn 3 (boryl) 2 ]. The latter then dimerizes to give the observed hexametallic product 4, with independent studies showing that similar trigermanium species aggregate in analogous fashion., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The synthesis and the first structural characterization of the halogenated pyridinium salts [C 5 F 5 NH] + , [C 5 F 4 ClNH] + , [(C 5 F 5 N) 2 H] + , [(C 5 Cl 5 N) 2 H] + of the weakly coordinating anion (WCA) [Al(OTeF 5 ) 4 ] - , showing noncovalent interactions in the solid state, are presented. The salts were characterized by the multinuclear NMR and IR spectroscopy as well as X-ray diffraction. Hirshfeld surface analysis and solid state structures reveal various intermolecular anion-π and σ-hole interactions between the corresponding halogenated pyridinium cations and the anion [Al(OTeF 5 ) 4 ] - ., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

A systematic study to access stable stannaimines is reported, by combining different heteroleptic stannylenes with a range of organic azides. The reactions of terphenyl-/hypersilyl-substituted stannylenes yield the putative tin nitrogen double bond, but is directly followed by 1,2-silyl migration to give Sn II systems featuring bulky silylamido ligands. By contrast, the transition from a two σ donor ligand set to a mixed σ-donor/π-donor scaffold allows access to three new stannaimines which can be handled at room temperature. The reactivity profile of these Sn=N bonded species is crucially dependent on the substituent at the nitrogen atom. As such, the Sn=NMes (Mes=2,4,6-Me 3 C 6 H 2 ) system is capable of activating a broad range of substrates under ambient conditions via 1,2-addition reactions, [2+2] and [4+2] cycloaddition reactions. Most interestingly, very rare examples of main group multiple bond metathesis reactions are also found to be viable., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The reaction of amido-substituted stannylenes with phospha-Wittig reagents (Me 3 PPR) results in release of hexamethyldisilazane and tethering of the resulting -CH 2 PMe 2 PR fragment to the tin center to give P-donor stabilized stannylenes featuring four-membered Sn , C , P , P heterocycles. Through systematic increases in steric loading, the structures of these systems in the solid state can be tuned, leading to successive P-P bond lengthening and Sn-P contraction and, in the most encumbered case, to complete P-to-Sn transfer of the phosphinidene fragment. The resulting stannaphosphene features a polar Sn═P double bond as determined by structural and computational studies. The reversibility of phosphinidene transfer can be established by solution phase measurements and reactivity studies.

By employing the highly reducing aluminyl complex [K{(NON)Al}] 2 (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene), we demonstrate the controlled formation of P 4 2- and P 4 4- complexes from white phosphorus, and chemically reversible inter-conversion between them. The tetra-anion features a unique planar π-bonded structure, with the incorporation of the K + cations implicit in the use of the anionic nucleophile offering additional stabilization of the unsaturated isomer of the P 4 4- fragment. This complex is extremely reactive, acting as a source of P 3- : exposure to ammonia leads to the release of phosphine (PH 3 ) under mild conditions (room temperature and pressure), which contrast with those necessitated for the direct combination of P 4 and NH 3 (>5 kbar and >250 °C)., (© 2021 Wiley-VCH GmbH.)

Trifluoromethylation of [AuF 3 (SIMes)] with the Ruppert-Prakash reagent TMSCF 3 in the presence of CsF yields the product series [Au(CF 3 ) x F 3-x (SIMes)] (x=1-3). The degree of trifluoromethylation is solvent dependent and the ratio of the species can be controlled by varying the stoichiometry of the reaction, as evidenced from the 19 F NMR spectra of the corresponding reaction mixtures. The molecular structures in the solid state of trans-[Au(CF 3 )F 2 (SIMes)] and [Au(CF 3 ) 3 (SIMes)] are presented, together with a selective route for the synthesis of the latter complex. Correlation of the calculated SIMes affinity with the carbene carbon chemical shift in the 13 C NMR spectrum reveals that trans-[Au(CF 3 )F 2 (SIMes)] and [Au(CF 3 ) 3 (SIMes)] nicely follow the trend in Lewis acidities of related organo gold(III) complexes. Furthermore, a new correlation between the Au-C carbene bond length of the molecular structure in the solid state and the chemical shift of the carbene carbon in the 13 C NMR spectrum is presented., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Molecular alkali tetrafluorido aurate ion pairs M[AuF 4 ] (M=K, Rb, Cs) are produced by co-deposition of IR laser-ablated AuF 3 and MF in solid neon under cryogenic conditions. This method also yields molecular AuF 3 and its dimer Au 2 F 6 . The products are characterized by their Au-F stretching bands and high-level quantum-chemical calculations at the CCSD(T)/triple-ζ level of theory. Structural changes in AuF 4 - associated with the coordination of the anion to different alkali cations are proven spectroscopically and discussed., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The synthesis and structural characterisation of the difluorido organo gold(iii) complexes [AuClF2(SIMes)] and [AuF2(OTeF5)(SIMes)] are presented. The substitution of a fluorido ligand in [AuF3(SIMes)] by an OTeF5 group increases the Lewis acidity of the Au moiety. A scale for carbene affinities is presented, which correlates calculated and experimental values for the Lewis acidity of the metal centre in akin compounds.

Two different reaction routes are described to access the unprecedented trifluoridoorganogold(III) complex [AuF 3 (SIMes)]. The compound bears the N-heterocyclic carbene SIMes (1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) as a ligand for a molecular Lewis acidic AuF 3 unit and was characterized by NMR spectroscopy as well as X-ray crystallography. Apart from the use of a [AuF 4 ] - salt as precursor, the strong oxidizing compound AuF 3 can be employed neat as starting material. The reaction proceeded even in organic solvents in the presence of SIMes as the ligand precursor. Decomposition reactions with the solvent can, therefore, be prevented by using this strategy., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis of [NMe 4 ][AuF 4 ] and [NEt 4 ][AuF 4 ], as well as an improved one-pot synthesis of Cs[AuF 4 ], is reported. The new [AuF 4 ] - salts were structurally characterized by single crystal X-ray diffraction, NMR spectroscopy, vibrational spectroscopy, and mass spectrometry. These salts are the first gold(III) fluoride salts that can be isolated in pure form and are convenient to be used in usual organic solvents for subsequent synthesis. The formation of molecular AuF 3 complexes in solution is further reported, characterized as [F 3 Au(NCCH 3 )] at low temperature, as [F 3 Au(py)] and a binuclear derivative which are stable at room temperature. The stability of these species in common organic solvents was investigated and they showed a satisfying stability., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)