Donor Acceptor Complexes between the Chalcogen Fluorides SF2 , SeF2 , SeF4 and TeF4 and an N-Heterocyclic Carbene.

The majority of binary chalcogen fluorides are fiercely reactive and extremely difficult to handle. Here, we show that access to crystalline donor-acceptor complexes between chalcogen difluorides (sulfur, selenium) and tetrafluorides (selenium, tellurium) with the N-heterocyclic carbene (NHC) 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) is possible conveniently and safely without the need to generate the highly unstable EF2 (E=S, Se) or the very toxic and corrosive SeF4 .

Bulky Polyfluorinated Terphenyldiphenylboranes: Water Tolerant Lewis Acids.

Protocols for the synthesis of the bulky polyfluorinated triarylboranes 2,6-(C6 F5 )2 C6 F3 B(C6 F5 )2 (1), 2,6-(C6 F5 )2 C6 F3 B[3,5-(CF3 )2 C6 H3 ] (2), 2,4,6-(C6 F5 )3 C6 H2 B(C6 F5 )2 (3), 2,4,6-(C6 F5 )3 C6 H2 B[3,5-(CF3 )2 C6 H3 ] (4) were developed. All boranes are water tolerant and according to the Gutmann-Beckett method, 1-3 display Lewis acidities larger than that of the prominent B(C6 F5 )3 .

Cationic Carbene Analogues: Donor-Free Phosphenium and Arsenium Ions.

Carbenes and their analogues have constantly enthralled chemists with their intriguing reactivity of ambiphilic character stemming from their electronic structures. Phosphenium and arsenium ions are fiercely reactive cationic species, the stabilization of which has been so far achieved in the condensed phase by dispersing the positive charge through electromeric conjugation with at least one electron-rich substituent (frequently amido groups). Although observed in the gas phase, the isolation of dicoordinate phosphenium and arsenium ions lacking such stabilizing ligands has eluded chemists for decades. Herein we show that by judicious choice of aromatic substituents, dicoordinate, donor-free, Lewis-superacidic phosphenium and arsenium ions can be kinetically stabilized. They feature singlet electronic ground states possessing a vacant p-orbital and an electron lone pair with predominantly s-character.

A Small Cationic Organo-Copper Cluster as Thermally Robust Highly Photo- and Electroluminescent Material.

Organic light-emitting diodes (OLEDs) are revolutionizing display applications. In this aspect, luminescent complexes of precious metals such as iridium, platinum, or ruthenium still playing a significant role. Emissive compounds of earth-abundant copper with equivalent performance are desired for practical, large-scale applications such as solid-state lighting and displays. Copper(I)-based emitters are well-known to suffer from weak spin-orbit coupling and a high reorganization energy upon photoexcitation. Here we report a cationic organo-copper cluster [Cu4(PCP)3]+ (PCP = 2,6-(PPh2)2C6H3) that features suppressed nonradiative decays, giving rise to a robust narrow-band green luminophore with a photoluminescent (PL) efficiency up to 93%. PL decay kinetics corroborated by DFT calculations reveal a complex emission mechanism involving contributions of both thermally activated delayed fluorescence and phosphorescence. This robust compound was solution-processed into a thin film in prototype OLEDs with external quantum efficiency up to 11% and a narrow emission bandwidth (65 nm fwhm).

Tri- and Tetranuclear Metal-String Complexes with Metallophilic d10 -d10 Interactions.

The reaction of 2,6-F2 C6 H3 SiMe3 with Ph2 PLi provided 2,6-(Ph2 P)2 C6 H3 SiMe3 (1), which can be regarded as precursor for the novel anionic tridentate ligand [2,6-(Ph2 P)2 C6 H3 ]- (PCP)- . The reaction of 1 with [AuCl(tht)] (tht=tetrahydrothiophene) afforded 2,6-(Ph2 PAuCl)2 C6 H3 SiMe3 (2). The subsequent reaction of 2 with CsF proceeded with elimination of Me3 SiF and yielded the neutral tetranuclear complex linear-[Au4 Cl2 (PCP)2 ] (3) comprising a string-like arrangement of four Au atoms. Upon chloride abstraction from 3 with NaBArF 4 (ArF =3,5-(CF3 )2 C6 H3 ) in the presence of tht, the formation of the dicationic tetranuclear complex linear-[Au4 (PCP)2 (tht)2 ](BArF 4 )2 (4) was observed, in which the string-like structural motif is retained. Irradiation of 4 with UV light triggered a facile rearrangement in solution giving rise to the dicationic tetranuclear complex cyclo-[Au4 (PCP)2 (tht)2 ](BArF 4 ) (5), which comprises a rhomboidal motif of four Au atoms. In 3-5, the Au atoms are associated by a number of significant aurophilic interactions. The atom-economic and selective reaction of 3 with HgCl2 yielded the neutral trinuclear bimetallic complex [HgAu2 Cl3 (PCP)] (6) comprising significant metallophilic interactions between the Au and Hg atoms. Therefore, 6 may be also regarded as a metallopincer complex [ClHg(AuCAu)] between HgII and the anionic tridentate ligand [2,6-(Ph2 PAuCl)2 C6 H3 ]- (AuCAu)- containing a central carbanionic binding site and two "gold-arms" contributing pincer-type chelation trough metallophilic interactions. Compounds 1-6 were characterized experimentally by multinuclear NMR spectroscopy and X-ray crystallography and computationally using a set of real-space bond indicators (RSBIs) derived from electron density (ED) methods including Atoms In Molecules (AIM), the Electron Localizability Indicator (ELI-D) as well as the Non-Covalent Interaction (NCI) Index.

The Bis(ferrocenyl)phosphenium Ion Revisited.

The bis(ferrocenyl)phosphenium ion, [Fc2 P]+ , reported by Cowley et al. (J. Am. Chem. Soc. 1981, 103, 714-715), was the only claimed donor-free divalent phosphenium ion. Our examination of the molecular and electronic structure reveals that [Fc2 P]+ possesses significant intramolecular Fe⋅⋅⋅P contacts, which are predominantly electrostatic and moderate the Lewis acidity. Nonetheless, [Fc2 P]+ undergoes complex formation with the Lewis bases PPh3 and IPr to give the donor-acceptor complexes [Fc2 P(PPh3 )]+ and [Fc2 P(IPr)]+ (IPr=1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene).

Intramolecular Reaction of Transient Phosphenium and Arsenium Ions Giving Rise to Isolable 9-Phospha- and 9-Arsena-Fluorenium Ions.

Transient phosphenium and arsenium ions, generated by fluoride abstraction from bis(m-terphenyl)fluoropnictogens, underwent intramolecular electrophilic attack prior to methyl group migration and gave rise to isolable 9-phospha- and 9-arsena-fluorenium ions.

Transient Phosphenium and Arsenium Ions versus Stable Stibenium and Bismuthenium Ions.

Fluoride abstraction from bis-m-terphenylelement fluorides (2,6-Mes2 C6 H3 )2 EF (E=P, As) generated the highly reactive phosphenium ion [(2,6-Mes2 C6 H3 )2 P]+ and the arsenium ion [(2,6-Mes2 C6 H3 )2 As]+ , which immediately underwent intramolecular electrophilic substitution and formation of an 1,2,4-trimethyl-6-mesityl-5-m-terphenyl-benzo[b]phospholium ion and an 1,2,4-trimethyl-6-mesityl-5-m-terphenyl-benzo[b]arsolium ion, respectively. The formation of the latter involved a methyl group migration from the ortho-position of a flanking mesityl group to the meta-position. This reactivity of [(2,6-Mes2 C6 H3 )2 E]+ (E=P, As) is in sharp contrast to the related stibenium ion [(2,6-Mes2 C6 H3 )2 Sb]+ and bismuthenium ion [(2,6-Mes2 C6 H3 )2 Bi]+ , which have been recently isolated and fully characterized (Angew. Chem. Int. Ed. 2018, 57, 10080-10084). On the basis of DFT calculations, a mechanism for the rearrangement of the phosphenium and arsenium ions into the phospholium and arsolium ions is proposed, which is not feasible for the stibenium and bismuthenium ions.

Functionalized Fluorophosphonium Ions.

Efforts to prepare an elusive donor-free phosphenium ion, [R2 P]+ , led us to synthesize functionalized fluorophosphonium cations of the type [R2 P(F)X]+ (X=SiEt3 , H, F), which were obtained from the related neutral fluorophosphines R2 PF and R2 PF3 upon protonation and reaction with solvated [Et3 Si]+ ions (R=2,6-Mes2 C6 H3 ). The hypothetical reductive elimination of [R2 P(F)SiEt3 ]+ and [R2 P(F)H]+ affording [R2 P]+ , Et3 SiF and HF, respectively, was calculated to be endothermic by 40.1 and 190.6 kJ mol-1 .

Heavy Carbene Analogues: Donor-Free Bismuthenium and Stibenium Ions.

Kinetically stabilized congeners of carbenes, R2 C, possessing six valence electrons (four bonding electrons and two non-bonding electrons) have been restricted to Group 14 elements, R2 E (E=Si, Ge, Sn, Pb; R=alkyl or aryl) whereas isoelectronic Group 15 cations, divalent species of type [R2 E]+ (E=P, As, Sb, Bi; R=alkyl or aryl), were unknown. Herein, we report the first two examples, namely the bismuthenium ion [(2,6-Mes2 C6 H3 )2 Bi][BArF4 ] (1; Mes=2,4,6-Me3 C6 H2 , ArF =3,5-(CF3 )2 C6 H3 ) and the stibenium ion [(2,6-Mes2 C6 H3 )2 Sb][B(C6 F5 )4 ] (2), which were obtained by using a combination of bulky meta-terphenyl substituents and weakly coordinating anions.

A Monoaryllead Trichloride That Resists Reductive Elimination.

Transmetallation of Pb(OAc)4 with R2 Hg (1), followed by treatment with HCl in Et2 O, provided RPbCl3 (2), the first kinetically stabilized monoorganolead trihalide that resists reductive elimination under ambient conditions. The kinetic stabilisation relies on an intramolecularly coordinating O-donor substituent (R=6-Ph2 P(O)-Ace-5-). The gram-scale preparation of 2 was key for the synthesis of unsymmetrically substituted diaryllead dichlorides RR'PbCl2 (3 a, R'=Ph; 3 b, R'=4-MeOC6 H4 ; 3 c, R'=4-Me2 NC6 H4 ).

Mapping the Trajectory of Nucleophilic Substitution at Silicon Using a peri-Substituted Acenaphthyl Scaffold.

The second-order nucleophilic substitution (SN 2) reaction at a silicon atom is scrutinized by means of snapshots along a pseudoreaction coordinate. Phosphine and fluoride represent both attacking and leaving groups in the modeled SN 2 reaction. In the experimentally obtained 5-diphenylphosphinoacenaphth-6-yl-dimethylfluorosilane, 1, the phosphine and fluorosilane moieties are forced into immediate proximity through an acenaphthyl scaffold, that is, they exhibit peri interactions that serve as the model of the reactant ion-molecule complex and starting point for a theoretical potential-energy surface (PES) scan. Upon dissociation of fluoride, the experimentally obtained silylphosphonium cation 2 serves as a model of the product and end point of the PES scan. The pseudoreaction pathway is studied using geometric, energetic, spectroscopic, molecular-orbital, and topological real-space bonding indicators. It becomes evident that it is crucial to combine such methods to understand the pseudoreaction because they reveal different aspects based on different sensitivity to dispersive, electrostatic, and polar-covalent contributions to bonding, as shown by the reduced density gradient analysis. For example, atoms-in-molecules theory describes a late topological catastrophe, whereas the electron localizability indicator describes an early concerted reaction and natural resonance theory describes a more gradual change of properties. This case study encourages the use of a well-balanced toolbox equipped with complementary methods to emphasize different aspects of bonding.

The Weakly Coordinating Tris(trichlorosilyl)silyl Anion.

Closely following the procedure for the preparation of the base-stabilized dichlorosilylene complex NHCDipp ⋅SiCl2 reported by Roesky, Stalke, and co-workers (Angew. Chem. Int. Ed. 2009, 48, 5683-5686), a few crystals of the salt [NHCDipp -H⋅⋅⋅Cl⋅⋅⋅H-NHCDipp ]Si(SiCl3 )3 were isolated, aside from the reported byproduct [NHCDipp -H+ ⋅⋅⋅Cl- ], and characterized by X-ray crystallography (NHCDipp =N,N-di(2,6-diisopropylphenyl)imidazo-2-ylidene). They contain the weakly coordinating anion Si(SiCl3 )3- , which was also obtained in high yields upon deprotonation of the conjugate Brønsted acid HSi(SiCl3 )3 with NHCDipp or PMP (PMP=1,2,2,6,6-pentamethylpiperidine). The acidity of HSi(SiCl3 )3 was estimated by DFT calculations to be substantially higher than those of other H-silanes. Further DFT studies on the electronic structure of Si(SiCl3 )3- , including the electrostatic potential and the electron localizability, confirmed its low basicity and nucleophilicity compared with other silyl anions.

Synthesis of a stable crystalline nitrene.

Nitrenes are a highly reactive, yet fundamental, compound class. They possess a monovalent nitrogen atom and usually a short life span, typically in the nanosecond range. Here, we report on the synthesis of a stable nitrene by photolysis of the arylazide MSFluindN3 (1), which gave rise to the quantitative formation of the arylnitrene MSFluindN (2) (MSFluind is dispiro[fluorene-9,3'-(1',1',7',7'-tetramethyl-s-hydrindacen-4'-yl)-5',9''-fluorene]) that remains unchanged for at least 3 days when stored under argon atmosphere at room temperature. The extraordinary life span permitted the full characterization of 2 by single-crystal x-ray crystallography, electron paramagnetic resonance spectroscopy, and superconducting quantum interference device magnetometry, which supported a triplet ground state. Theoretical simulations suggest that in addition to the kinetic stabilization conferred by the bulky MSFluind aryl substituent, electron delocalization across the central aromatic ring contributes to the electron stabilization of 2.

(2,4,6-Trimethyl-phen-yl)boronic acid-triphenyl-phosphine oxide (1/1).

In the crystal structure of the title compound, C(9)H(13)BO(2)·C(18)H(15)OP, there are O-H⋯O hydrogen bonds between the O atom of triphenyl-phosphine oxide and one hy-droxy group of the boronic acid. Boronic acid mol-ecules form inversion-related hydrogen-bonded dimers in an R(2) (2)(8) motif. The structure is consolidated by inter-molecular C-H⋯O bonds and C-H⋯π inter-actions.

2'-Iodo-2,2'',3,3'',4,4'',5,5'',6,6''-deca-methyl-1,1':3',1''-terphenyl chloro-form monosolvate.

The title compound, C(28)H(33)I·CHCl(3), forms dimers through C-I⋯π inter-actions. The crystal structure is consolidated by the presence of C-H⋯π inter-actions between the chloro-form solvent and the main mol-ecule.

3,5-Dibromo-2',3',4',5',6'-penta-methyl-1,1'-biphen-yl.

In the crystal structure of the title compound, C(17)H(18)Br(2), the benzene rings are almost perpendicular [dihedral angle = 84.0 (3)°]. The crystal structure is consolidated by the presence of C-Br⋯π inter-actions.

Taking a snapshot of the triplet excited state of an OLED organometallic luminophore using X-rays.

OLED technology beyond small or expensive devices requires light-emitters, luminophores, based on earth-abundant elements. Understanding and experimental verification of charge transfer in luminophores are needed for this development. An organometallic multicore Cu complex comprising Cu-C and Cu-P bonds represents an underexplored type of luminophore. To investigate the charge transfer and structural rearrangements in this material, we apply complementary pump-probe X-ray techniques: absorption, emission, and scattering including pump-probe measurements at the X-ray free-electron laser SwissFEL. We find that the excitation leads to charge movement from C- and P- coordinated Cu sites and from the phosphorus atoms to phenyl rings; the Cu core slightly rearranges with 0.05 Å increase of the shortest Cu-Cu distance. The use of a Cu cluster bonded to the ligands through C and P atoms is an efficient way to keep structural rigidity of luminophores. Obtained data can be used to verify computational methods for the development of luminophores.

Chloridobis{2-[(dimethyl-amino)-meth-yl]phen-yl}anti-mony(III).

In the title compound, [Sb(C(9)H(12)N)(2)Cl], the Sb atom adopts a Ψ-trigonal-bipyramidal geometry. The two 2-[(dimethyl-amino)-methyl]-phenyl ligands are coordinated asymmetrically to the Sb atom. The carbon atoms of one of the ligands are disordered over sets of sites with equal occupancy, resulting in two conformational isomers in the crystal. The Sb-C and Sb-N distances in the ordered ligand are: 2.153 (4) and 3.326 (5) Å, respectively. The corresponding distances in the disordered ligand are: 2.103 (5)/2.188 (5) and 2.454 (3) Å, respectively. The structure displays intra-molecular C-H⋯Cl hydrogen bonding.

Transmetallation of bis(6-diphenylphosphinoxy-acenapth-5-yl)mercury with tin tetrachloride, antimony trichloride and bismuth trichloride.

We recently communicated (Angew. Chem. Int. Ed., 2018, 57, 5917-5920) the transmetallation of [6-Ph2P(O)-Ace-5-]2Hg (1) with Pb(OAc)4, which, after work-up with HCl in Et2O, provided the first aryl lead trichloride, 6-Ph2P(O)-Ace-5-PbCl3 (2), and 6-Ph2P(O)-Ace-5-HgCl (3). With LiCl, 1 forms a complex, [{[6-Ph2P(O)-Ace-5]2Hg}2Li]Cl (1a), that shows no reactivity towards Pb(OAc)4 anymore, which highlights the role of the intramolecularly coordinated P(O) functionality in transmetallation. In this work, we have broadened the scope of the transmetallation reagent by the reaction of 1 with SnCl4, SbCl3 and BiCl3 giving rise to the formation of 6-Ph2P(O)-Ace-5-SnCl3 (4), 6-Ph2P(O)-Ace-5-SbCl2 (5) and 6-Ph2P(O)-Ace-5-BiCl2 (6), respectively. The high Lewis acidity permits 4 and 5 to undergo complexation with THF, whereas no such complexes were formed with 2 and 6. The molecular structures of 1a, 3, 4, 4·THF, 5, 5·THF and 6 were established by X-ray crystallography. The different P-O distances of 2, 4, 4·THF, 5, 5·THF and 6, reflecting the relative strength of the P(O)E coordination (E = Pb, Sn, Sb, Bi), were discussed. The nature of the P(O)E interactions of 2, 4, 4·THF, 5, 5·THF and 6 was studied using a set of real-space bond indicators (RSBIs).