Complexes of adamantane-based group 13 Lewis acids and superacids: Bonding analysis and thermodynamics of hydrogen splitting

The electronic structure and chemical bonding in donor-acceptor complexes formed by group 13 element adamantane and perfluorinated adamantane derivatives EC9R15 (E=B, Al; R=H, F) with Lewis bases XR3 and XC9H15 (X=N, P; R= H, CH3) have been studied using energy decomposition analysis at the BP86/TZ2P level of theory. Larger stability of complexes with perfluorinated adamantane derivatives is mainly due to better electrostatic and orbital interactions. Deformation energies of the fragments and Pauli repulsion are of less importance, with exception for the boron-phosphorus complexes. The MO analysis reveals that LUMO energies of EC9R15 significantly decrease upon fluorination (by 4.7 and 3.6 eV for E=B and Al, respectively) which results in an increase of orbital interaction energies by 27-38 (B) and 15-26 (Al) kcal mol(-1). HOMO energies of XR3 increase in order PH3<NH3<PMe3<PC9H15<NMe3<NC9H15. For the studied complexes, there is a linear correlation between the dissociation energy of the complex and the energy difference between HOMO of the donor and LUMO of the acceptor. The fluorination of the Lewis acid significantly reduces standard enthalpies of the heterolytic hydrogen splitting H-2+D+A=[HD](+)+[HA](-). Analysis of several types of the [HD](+)center dot center dot center dot[HA](-) ion pair formation in the gas phase reveals that structures with additional H center dot center dot center dot F interactions are energetically favorable. Taking into account the ion pair formation, hydrogen splitting is predicted to be highly exothermic in case of the perfluorinated derivatives both in the gas phase and in solution. Thus, fluorinated adamantane-based Lewis superacids are attractive synthetic targets for the construction of the donor-acceptor cryptands

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

The reaction behavior of [Cp*Fe(η5-As5)] (I) (Cp*=C5Me5) 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-As5NHC)] (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 EtCAAC (EtCAAC=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(AsEtCAAC)4] (2). The reaction of (LE)2 (L=PhC(NtBu)2; E=Si, Ge) with I resulted in a rearrangement and an insertion of LE fragments, forming unique silicon- (4: [Cp*Fe(η4-As4SiL)], 5 a: [Cp*Fe(η4-As6SiL)) and germanium-containing (5 b: [Cp*Fe(η4-As6GeL)) cyclic polyarsenic ligand complexes

Reactivity of the stibinidene complex [ClSb{Cr(CO) 5 } 2 (thf)]

Stibinidene complexes are rare and highly sensitive low-valent main group compounds, which have not been studied extensively for their reaction behavior so far. In the reaction with GaCl3, the stibinidene complex [ClSb{Cr(CO)5}2(thf)] (1) shows a dimerization to [ClSb{Cr(CO)5}2]2 (2) and yields the anionic double-chlorinated compound [Cl2Sb{Cr(CO)5}2]− (3) in the reaction with different ionic nucleophiles. When using neutral nucleophiles (such as amines, isocyanides and phosphines) as reaction partners, tetrahedral complexes of the type [ClSb{Cr(CO)5}2Nu] (4: Nu=NH2Mes; 5: Nu=CN(dmp); 6: Nu=PPh3; 7: Nu=PPh2H) are formed which can be used in subsequent reactions. All of these products are among the first of their type to be synthesized and isolated

Stepwise activation of “non-innocent” Cp* substituents – a Cp* based cascade reaction

Reactions of Cp* substituted pentelidene complexes with the primary phosphine Cp*PH2 yield novel polycyclic phosphorus/arsenic and carbon containing cage compounds via cascade-like reactions. These reactions include a sequence of nucleophilic addition reactions, intramolecular hydrophosphination (partially hydroarsination) reactions, retro-Diels–Alder reactions with Cp*H elimination and subsequent [2+4]-cycloadditions

NHC-stabilized Parent Arsanylalanes and –gallanes. NHC-stabilisierte Stammverbindungen der Arsanylalane und -gallane

The synthesis and characterization of the unprecedented compounds IDipp⋅E′H2AsH2 (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′H2Cl (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⋅GaH2AsPh2 (1) and IDipp⋅AlH2AsPh2 (2) were obtained by the reaction of KAsPh2 with IDipp⋅E′H2Cl (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

Coordination of Pnictogenylboranes Towards Tl(I) Salts and a Tl‐ Mediated P−P Coupling

The coordination chemistry of only Lewis-base (LB)-stabilized pnictogenylboranes EH2BH2⋅NMe3 (E=P, As) towards Tl(I) salts has been studied. The reaction of Tl[BArCl] (BArCl=[B(3,5-C6H3Cl2)4]−) with the corresponding pnictogenylborane results in the formation of [Tl(EH2BH2⋅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 EH2BH2 ⋅ NMe3 in [Tl(EH2BH2 ⋅ 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 PH2BH2⋅NMe3, a Tl(I)-mediated P−P coupling takes place in CH2Cl2 as solvent resulting in [Me3N⋅BH2PH2PHBH2⋅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

Characterization of the Ligand Properties of Donor‐stabilized Pnictogenyltrielanes

A general synthesis and the characterization of novel alkyl-substituted NHC-stabilized pnictogenylboranes NHC ⋅ BH2ER2 (NHC=N-heterocyclic carbene, E=P, As; R2=Me2, Ph2, tBuH, Cy2, (SiMe3)2) are reported. These compounds were reacted with Ni(CO)4 to the corresponding complexes of the type [(NHC ⋅ BH2ER2)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

Reaktivität von [Cp*Fe(η5‐As5)] gegenüber Carbenen, Silylenen und Germylenen

Das Reaktionsverhalten von [Cp*Fe(η5-As5)] (I) (Cp*=C5Me5) gegenüber Carbenen und ihren schwereren Analoga wurde untersucht. Die Reaktion von I mit NHCs (NHCs=N-heterocyclische Carbene) gibt die ersten Substitutionsprodukte von Polyarsen-Ligandkomplexen mittels NHCs [Cp*Fe(η4-As5NHC)] (1 a: NHC=IMe=1,3,4,5-Tetramethylimidazolin-2-yliden, 1 b: NHC=IMes=1,3-Bis(2,4,6-trimethylphenyl)-imidazolin-2-yliden). Im Gegensatz dazu führt die Reaktion von I mit EtCAAC (EtCAAC=2,6-Diisopropylphenyl)-4,4-diethyl-2,2-dimethyl-pyrrolidin-5-yliden) zu einer Fragmentierung und Bildung einer neuartigen As6-sägebockartigen Verbindung [As2(AsEtCAAC)4] (2). Die Reaktion von (LE)2 (L=PhC(NtBu)2; E=Si, Ge) mit I resultiert in einer Umlagerung und einer Insertion von LE-Fragmenten, was zur Bildung einzigartiger silizium- (4: [Cp*Fe(η4-As4SiL)], 5 a: [Cp*Fe(η4-As6SiL)) und germanium-haltiger (5 b: [Cp*Fe(η4-As6GeL)) cyclischer Polyarsen-Ligandkomplexe führt

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

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 ⋅ GeH2BH2OTf (1) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) led to mixtures of the two isomers IDipp ⋅ GeH2BH2PH2 (2 a) and IDipp ⋅ BH2GeH2PH2 (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 ⋅ GeH2BH2 ⋅ IDipp][PHGeH2BH2PH2BH2GeH2] (4) that contains the novel anionic cyclohexyl-like inorganic heterocycle [PHGeH2BH2PH2BH2GeH2]−. In addition, the borane adducts IDipp ⋅ GeH2BH2PH2BH3 (3 a) and IDipp ⋅ BH2GeH2PH2BH3 (3 b) as even longer chain compounds were obtained from reactions of 2 a/2 b with H3B ⋅ 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