Structures and stability of I2 and ICl complexes with pyridine: Ab initio and DFT study.

Theoretical investigation of thermodynamic stability and bonding features of possible isomers of the molecular and ionic complexes of pyridine with molecular iodine and iodine monochloride IX (X = I,Cl) is presented. M06-2X DFT functional is found to provide bond distances and dissociation energies which are close to those obtained at high-level ab initio CCSD(T)/aug-cc-pvtz//CCSD/aug-cc-pvtz benchmark computations for the most stable isomers, formed via donation of a lone pair of nitrogen atom of pyridine to the iodine atom. These isomers are by 23-33 kJ mol-1 (in case of I2) and by 39-56 kJ mol-1 (in case of ICl) more stable than other molecular complexes. T-shaped π-σ* bonded isomers turn out to be energetically comparable with van der Waals bound compounds. Among the ionic isomers, structures featuring [IPy2]+ cation with I3 - or ICl2 - counterions are more stable. Oligomerization favors ionic isomers starting from the tetrameric clusters of the composition (IX)4Py4.

The Field of Main Group Lewis Acids and Lewis Superacids: Important Basics and Recent Developments.

New developments in the field of Lewis acidity are highlighted, with the focus of novel Lewis acids and Lewis superacids of group 2, 13, 14, and 15 elements. Several important basics, illustrated by modern examples (classification of Donor-Acceptor (DA) complexes, amphoteric nature of any compound in terms of DA interactions, reorganization energies of main group Lewis acids and the role of the energies of frontier orbitals) are presented and discussed. It is emphasized that the Lewis acidity phenomena are general and play vital role in different areas of chemistry: from weak "atomophilic" interactions to the complexes of Lewis superacids.

Characterization of the Ligand Properties of Donor-stabilized Pnictogenyltrielanes.

A general synthesis and the characterization of novel alkyl-substituted NHC-stabilized pnictogenylboranes NHC ⋅ BH2 ER2 (NHC=N-heterocyclic carbene, E=P, As; R2 =Me2 , Ph2 , t BuH, Cy2 , (SiMe3 )2 ) are reported. These compounds were reacted with Ni(CO)4 to the corresponding complexes of the type [(NHC ⋅ BH2 ER2 )Ni(CO)3 ] to determine their donor strength by Tolman Electronic Parameters (TEPs) and their steric demand as ligands compared to classical phosphines, superbasic phosphines and other commonly applied donor systems. The results show that the NHC-stabilized pnictogenyltrielanes can be considered as being highly basic, while their steric influence depends strongly on the organic residues as well as the donor attached to the {BH2 } moiety. Although weaker than commonly used superbasic phosphines, the donor strength of pnictogenyltrielanes in general can be classified as of similar strength as NHCs. The steric and electronic properties can easily be modified by alkyl substitution as evident from the TEP trends.

NHC-Stabilized Mixed Group 13/14/15 Element Hydrides.

The syntheses of novel N-heterocyclic carbene (NHC) adducts of group 13, 14 and 15 element hydrides are reported. Salt metathesis reactions between NaPH2 and IDipp ⋅ GeH2 BH2 OTf (1) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) led to mixtures of the two isomers IDipp ⋅ GeH2 BH2 PH2 (2 a) and IDipp ⋅ BH2 GeH2 PH2 (2 b); by altering the reaction conditions an almost exclusive formation of 2 b was achieved. Attempts to purify mixtures of 2 a and 2 b by re-crystallization from THF afforded a salt [IDipp ⋅ GeH2 BH2 ⋅ IDipp][PHGeH2 BH2 PH2 BH2 GeH2 ] (4) that contains the novel anionic cyclohexyl-like inorganic heterocycle [PHGeH2 BH2 PH2 BH2 GeH2 ]- . In addition, the borane adducts IDipp ⋅ GeH2 BH2 PH2 BH3 (3 a) and IDipp ⋅ BH2 GeH2 PH2 BH3 (3 b) as even longer chain compounds were obtained from reactions of 2 a/2 b with H3 B ⋅ SMe2 and were studied by NMR spectroscopy. Accompanying DFT computations give insight into the mechanism and energetics associated with 2 a/2 b isomerization as well as their decomposition pathways.

Reactivity of [Cp*Fe(η5 -As5 )] towards Carbenes, Silylenes and Germylenes.

The reaction behavior of [Cp*Fe(η5 -As5 )] (I) (Cp*=C5 Me5 ) towards carbenes and their heavier analogs was investigated. The reaction of I with NHCs (NHCs=N-heterocyclic carbenes) results in the first substitution products of polyarsenic ligand complexes by NHCs [Cp*Fe(η4 -As5 NHC)] (1 a: NHC=IMe=1,3,4,5-tetramethylimidazolin-2-ylidene, 1 b: NHC=IMes=1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene). In contrast, the reaction of I with Et CAAC (Et CAAC=2,6-diisopropylphenyl)-4,4-diethyl-2,2-dimethyl-pyrrolidin-5-ylidene) leads to a fragmentation and the formation of an unprecedented As6 -sawhorse-type compound [As2 (AsEt CAAC)4 ] (2). The reaction of (LE)2 (L=PhC(Nt Bu)2 ; E=Si, Ge) with I resulted in a rearrangement and an insertion of LE fragments, forming unique silicon- (4: [Cp*Fe(η4 -As4 SiL)], 5 a: [Cp*Fe(η4 -As6 SiL)) and germanium-containing (5 b: [Cp*Fe(η4 -As6 GeL)) cyclic polyarsenic ligand complexes.

Lewis acid stabilized group 13-15 element analogs of ethylene.

Stabilization of hydrogen-substituted group 13-15 compounds H2 EE'H2 (E = B, Al, Ga; E' = P, As, Sb) by Lewis acids is considered at B3LYP/def2-TZVP, B3LYP-D3/def2-TZVP and M06-2X/def2-TZVP levels of theory. It is shown, that for many Lewis acids additional reactivity beyond the DA complex formation with H2 EE'H2 monomer is expected. In case of complexation with E(C6 F5 )3 , F/H exchange reactions with group 13 bound hydrides are predicted to be exothermic and accompanied by the activation energies which are smaller than dissociation of the complex into components. In case of complex formation with transition metal (TM) carbonyls, additional O → Al, TM-C → Al interactions are observed, which in several cases lead to cyclic structures. The most promising candidates for the experimental studies have been identified. Synthetic approaches to the most promising LA-only stabilized compounds are recommended.

Coordination of Pnictogenylboranes Towards Tl(I) Salts and a Tl- Mediated P-P Coupling.

The coordination chemistry of only Lewis-base (LB)-stabilized pnictogenylboranes EH2 BH2 ⋅NMe3 (E=P, As) towards Tl(I) salts has been studied. The reaction of Tl[BArCl ] (BArCl =[B(3,5-C6 H3 Cl2 )4 ]- ) with the corresponding pnictogenylborane results in the formation of [Tl(EH2 BH2 ⋅NMe3 )][BArCl ] (1 a: E=P; 1 b: E=As). Whereas the Tl ion in 1 a/b is monocoordinated, the exchange of the weakly coordinating anion (WCA) in the Tl(I) salt leads to the formation of a trigonal pyramidal coordination mode at the Tl atom by coordination of three equivalents of EH2 BH2 ⋅ NMe3 in [Tl(EH2 BH2 ⋅ NMe3 )3 ][WCA] (2 a: E=P, WCA=TEFCl ; 2 b: E=As, WCA=TEF) (TEF=[Al{OC(CF3 )3 }4 ]- , TEFCl =[Al{(OC(CF3 )2 (CCl3 )}4 ]- ). Furthermore, by using two equivalents of PH2 BH2 ⋅NMe3 , a Tl(I)-mediated P-P coupling takes place in CH2 Cl2 as solvent resulting in [Me3 N⋅BH2 PH2 PHBH2 ⋅NMe3 ][WCA] (WCA=TEF, 3 a; BArCl , 3 b; TEFCl , 3 c). In contrast, for the arsenic derivatives 1 b and 2 b, no coupling reaction is observed. The underlying chemical processes are elucidated by quantum chemical computations.

Reactivity of Yellow Arsenic towards Cyclic (Alkyl)(Amino) Carbenes (CAACs).

Different cyclic (alkyl)(amino)carbenes (CAACs) were reacted with yellow arsenic. Several products [(CAAC-n)2 (µ,η1:1 -As2 )] (n=1 (1), 4 (2)), [(CAAC-2)3 (µ3 ,η1:1:1 -As4 )] (3) and [(CAAC-3)4 (µ4 ,η1:1:1:1 - As8 )] (6) were isolated due to the differing steric properties of CAAC-1-4. The products contain As2 , As4 or As8 units and represent the first examples of CAACs-substituted products of yellow arsenic. The reactivity of As4 was compared with the reactivities of P4 and the interpnictogen compound AsP3 , which led to a series of phosphorus-containing derivatives such as ([(CAAC-3)3 (µ3 ,η1:1:1 -P4 )] (4) and [(CAAC-3)4 (µ4 ,η1:1:1:1 -P8 )] (7)) and [(CAAC-3)3 (µ3 ,η1:1:1 -AsP3 )] (5). The products were characterized by spectroscopic and crystallographic methods and DFT computations were performed to clarify their formation pathway.

Three- and Five-Membered Anionic Chains of Pnictogenylboranes.

An unprecedented family of three- and five-membered substituted anionic derivatives of parent pnictogenylboranes is herein reported. Reacting various combinations of the pnictogenylboranes H2 E'-BH2 -NMe3 (E'=P, As) with pnictogen-based nucleophiles MER1R2 (E=P, As; R1=H, R2=t Bu; R1=R2=Ph; M=Na, K) allows for the isolation of the unsymmetrical products [Na(18-crown-6)][H2 E'-BH2 -EHt Bu] (3: E=E'=P; 4: E=E'=As; 5: E=As, E'=P) and [M(C)][H2 E'-BH2 -EPh2 ] (7: E=E'=P, M=Na, C=18-crown-6; 8: E=E'=As; M=K, C=[2.2.2]cryptand; 9: E=P, E'=As, M=Na, C=[2.2.2]cryptand; 10: E=As, E'=P, M=K, C=[2.2.2]cryptand). [Na(18-crown-6)][H2 As-BH2 -t BuPH-BH3 ] (6) is only accessible by a different pathway, using t BuPH2 , BH3 ⋅ SMe2 and NaNH2 as starting materials. Additionally, the synthesis of symmetrical diphenyl-substituted compounds [M(18-crown-6)][Ph2 E-BH2 -EPh2 ] (11: E=P, M=Na; 12: E=As, M=K) is reported which can be regarded as isostructural inorganic, negatively charged analogs of dppm (1,1-bis(diphenylphosphino)methane) and dpam (1,1-bis(diphenylarsino)methane). Furthermore, an elongation of the pnictogen boron backbone in compounds 3, 7 and 9' (similar compound to 9, stabilized however by 18-crown-6), is attainable by reacting them with the pnictogenylboranes H2 E'-BH2 -NMe3 leading to corresponding five-membered chain-like compounds [Na(18-crown-6)][H2 E-BH2 -R1R2P-BH2 -E'H2 ] (E=E'=P, R1=H, R2=t Bu (13); E=E'=P, R1=R2=Ph (14); E=E'=As, R1=R2=Ph (15); E=P, E'=As, R1=R2=Ph (16)). Finally, the thermodynamics of the reaction pathways were evaluated by quantum chemical computations.

Structures and Stability of Mixed Main Group Hydrides [PBEH6]n (E = C, Si, Ge; n = 1-4) and Donor-Acceptor Stabilization of Monomeric Chain Isomers.

Structures and stability of mixed group 13-14-15 element hydrides PBEH6 (E = C, Si, Ge), their oligomers, and complexes with Lewis acids and Lewis base are computationally studied at the B3LYP-D3/def2-TZVP level of theory. Unsubstituted chain hydrides are unstable and are expected to form cyclic oligomers. Cyclization can be prevented by the donor-acceptor complex formation. For complexes of chain hydrides with Lewis acid in many cases additional reactivity beyond the donor-acceptor complex formation is observed: cyclization and migration of terminal group from the group 13 Lewis acid to the boron or group 14 terminal atoms of the hydride. The most promising compounds for the experimental studies have been identified. Joint stabilization by both W(CO)5 and trimethylamine provides a synergetic effect, allowing stabilization of 13-14-15 chain compounds.

An NHC-Stabilized H2 GeBH2 Precursor for the Preparation of Cationic Group 13/14/15 Hydride Chains.

The synthesis, characterization and reactivity studies of the NHC-stabilized complex IDipp ⋅ GeH2 BH2 OTf (1) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) are reported. Nucleophilic substitution of the triflate (OTf) group in 1 by phosphine or arsine donors provides access to the cationic group 13/14/15 chains [IDipp ⋅ GeH2 BH2 ERR1 R2 ]+ (2 E=P; R, R1 =H; R2 =t Bu; 3 E=P; R=H; R1 , R2 =Ph; 4 a E=P; R, R1 , R2 =Ph; 4 b E=As; R, R1 , R2 =Ph). These novel cationic chains were characterized by X-ray crystallography, NMR spectroscopy and mass spectrometry. Moreover, the formation of the parent complexes [IDipp ⋅ GeH2 BH2 PH3 ][OTf] (5) and [IDipp ⋅ GeH3 ][OTf] (6) were achieved by reaction of 1 with PH3 . Accompanying DFT computations give insight into the stability of the formed chains with respect to their decomposition.

Influence of the solvent on the Lewis acidity of antimony pentahalides and group 13 Lewis acids toward acetonitrile and pyridine.

Energetic effects of solvation of SbF5 , SbCl5 , and 21 group 13 Lewis acids (LA) and their molecular complexes with acetonitrile and pyridine are evaluated using SMD approach. Compared to the gas phase, solvation increases the stability of boron- and aluminum-containing complexes but decreases the stability of gallium and indium-containing homologs due to larger solation energies of free LA. New Lewis acidity scales, based on the Gibbs energy of dissociation of the molecular complexes LA·pyridine and LA·acetonitrile in the gas phase, in benzene and acetonitrile solutions, are proposed.

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 .

Stability and Electronic Structure of Donor-Acceptor Stabilized Group 13/15 Oligomers.

Electronic structures and thermodynamic characteristics of chain inorganic group 13-15 oligomers [H2MEH2]n (M = B, Al, Ga, E = P, As; n = 4-15) are presented. Donor-acceptor interaction with both Lewis acids and Lewis bases effectively stabilizes chain isomers with respect to spontaneous cyclization and significantly changes their electronic structure.

NHC-stabilized Parent Arsanylalanes and -gallanes.

The synthesis and characterization of the unprecedented compounds IDipp⋅E'H2 AsH2 (E'=Al, Ga; IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) are reported, the first monomeric, parent representatives of an arsanylalane and arsanylgallane, respectively, stabilized only by a LB (LB=Lewis Base). They are prepared by a salt metathesis reaction of KAsH2 with IDipp⋅E'H2 Cl (E'=Al, Ga). The H2 -elimination pathway through the reaction of AsH3 with IDipp⋅E'H3 (E'=Al, Ga) was found to be a possible synthetic route with some disadvantages compared to the salt metathesis reaction. The corresponding organo-substituted compounds IDipp⋅GaH2 AsPh2 (1) and IDipp⋅AlH2 AsPh2 (2) were obtained by the reaction of KAsPh2 with IDipp⋅E'H2 Cl (E'=Al, Ga). The novel branched parent compounds IDipp⋅E'H(EH2 )2 (E'=Al, Ga; E=P, As) were synthesized by salt metathesis reactions starting from IDipp⋅E'HCl2 (E'=Al, Ga). Supporting DFT computations give insight into the different synthetic pathways and the stability of the products.

NHCs as Neutral Donors towards Polyphosphorus Complexes.

The first adducts of NHCs (=N-heterocyclic carbenes) with aromatic polyphosphorus complexes are reported. The reactions of [Cp*Fe(η5 -P5 )] (1) (Cp*=pentamethyl-cyclopentadienyl) with IMe (=1,3,4,5-tetramethylimidazolin-2-ylidene), IMes (=1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene) and IDipp (=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) led to the corresponding neutral adducts which can be isolated in the solid state. However, in solution, they quickly undergo a dissociative equilibrium between the adduct and 1 including the corresponding NHC. The equilibrium is influenced by the bulkiness of the NHC. [Cp''Ta(CO)2 (η4 -P4 )] (Cp''=1,3-di-tert-butylcyclopentadienyl) reacts with IMe under P atom abstraction to give an unprecedented cyclo-P3 -containing anionic tantalum complex. DFT calculations shed light onto the energetics of the reaction pathways.

Structures and Chemical Bonding in Antimony(III) Bromide Complexes with Pyridine.

Weakly or "partially" bonded molecules are an important link between the chemical and van der Waals interactions. Molecular structures of six new SbBr3 -Py complexes in the solid state have been determined by single-crystal X-ray diffraction analysis. In all complexes all Sb atoms adopt a pseudo-octahedral coordination geometry which is completed by additional Sb⋅⋅⋅Br contacts shorter than the sum of the van der Waals radii, with Br-Sb⋅⋅⋅Br angles close to 180°. To reveal the nature of Sb-Br and Sb-N interactions, the DFT calculations were performed followed by the analysis of the electrostatic potentials, the orbital interactions and the topological analysis. Based on Natural Bond Orbital (NBO) analysis, the Sb-Br interactions range from the covalent bonds to the pnictogen bonds. A simple structural parameter, non-covalence criterion (NCC) is defined as a ratio of the atom-atom distance to the linear combination of sums of covalent and van der Waals radii. NCC correlates with E(2) values for Sb-N, Sb-Cl and Sb-Br bonds, and appears to be useful criterion for a preliminary evaluation of the bonding situation.

Phosphanylalanes and Phosphanylgallanes Stabilized only by a Lewis Base.

The synthesis and characterization of the first parent phosphanylalane and phosphanylgallane stabilized only by a Lewis base (LB) are reported. The corresponding substituted compounds, such as IDipp⋅GaH2 PCy2 (1) (IDipp=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) were obtained by the reaction of LiPCy2 with IDipp⋅GaH2 Cl. However, the LB-stabilized parent compounds IDipp⋅GaH2 PH2 (3) and IDipp⋅AlH2 PH2 (4) were prepared via a salt metathesis of LiPH2 ⋅DME with IDipp⋅E'H2 Cl (E'=Ga, Al) or by H2 -elimination reactions of IDipp⋅E'H3 (E'=Ga, Al) and PH3 , respectively. The compounds could be isolated as crystalline solids and completely characterized. Supporting DFT computations gave insight into the reaction pathways as well as into the stability of these compounds with respect to their decomposition behavior.

Hydrogen splitting by pyramidalized 13-15 donor-acceptor cryptands: A computational study.

A series of new donor-acceptor cryptands, where pyramidalized donor (azaadamantane) and acceptor (bora/ala/adamantane) molecules are spatially oriented toward each other and linked via aromatic spacer, are constructed and computationally studied at M06-2X and ωB97X-D levels of theory. Kinetic stability of the perfluorinated bora- and ala-adamantane with respect to F migration to group 13 element is demonstrated. The effectiveness of the constructed cryptands, featuring pyramidalized perfluorinated acceptor moieties, in the heterolytic splitting of molecular hydrogen is predicted. Hydrogen splitting is highly exothermic and exergonic and is accompanied by small activation barriers. The most promising candidates for the experimental studies are identified. © 2019 Wiley Periodicals, Inc.

Monomeric ß-Diketiminato Group†13 Metal Dipnictogenide Complexes with Two Terminal EH2 Groups (E=P, As).

The pnictogenyl Group 13 compounds (Dipp2 Nacnac)M[E(SiMe3 )2 ]Cl and (Dipp2 Nacnac)M(EH2 )2 (Dipp2 Nacnac=HC[C(Me)N(Ar)]2 , Ar: Dipp=2,6-iPr2 C6 H3 ; M=Al, Ga, In; E=P, As) were successfully synthesized. The salt metathesis between (Dipp2 Nacnac)MCl2 and LiE(SiMe3 )2 only led to monosubstituted compounds (Dipp2 Nacnac)M[E(SiMe3 )2 ]Cl [E=P, M=Ga(1), In (2); E=As, M=Ga (3), In (4)], regardless of the stoichiometric ratios used. In contrast to the steric effect of the SiMe3 groups in 1-4, the reactions of the corresponding halides with LiPH2 ⋅DME (or KAsH2 ) facilely yielded the dipnictogenide compounds (Dipp2 Nacnac)M(EH2 )2 (E=P, M=Al (5), Ga (6), In (7); E=As, M=Al (8), Ga (9)), avoiding the use of flammable and toxic PH3 and AsH3 for their synthesis. The compounds 5-9 are the first examples of monomeric Group 13 diphosphanides and diarsanides in which the metal center is bound to two terminal PH2 and AsH2 groups, respectively. In contrast to the successful synthesis of the indium diphosphanide (Dipp2 Nacnac)In(PH2 )2 , the reaction of (Dipp2 Nacnac)InCl2 with KAsH2 led to an indium mirror due to the instability of the target product.