Trapping the Parent Inorganic Ethylenes H(2) SiGeH(2) and H(2) SiSnH(2) in the Form of Stable Adducts at Ambient Temperature

Putting on some weight: A series of stable adducts featuring the hitherto unknown mixed heavy ethylene analogues H(2) SiGeH(2) and H(2) SiSnH(2) were prepared using a versatile donor-acceptor method.     

Preparation of Stable Low‐Oxidation‐State Group 14 Element Amidohydrides and Hydride‐Mediated Ring‐Expansion Chemistry of N‐Heterocyclic Carbenes

Various low oxidation state (+2) group 14 element amidohydride adducts, IPr ? EH(BH₃)NHDipp (E=Si or Ge; IPr=[(HCNDipp)₂C:], Dipp=2,6‐iPr₂C₆H₃), were synthesized. Thermolysis of the reported adducts was investigated as a potential route to Si‐ and Ge‐based clusters; however, unexpected transmetallation chemistry occurred to yield the carbene–borane adduct, IPr ? BH₂NHDipp. When a solution of IPr ? BH₂NHDipp in toluene was heated to 100 °C, a rare C? N bond‐activation/ring‐expansion reaction involving the bound N‐heterocyclic carbene donor (IPr) transpired.     

Synthesis of Cationic R2P5+ Cages and Subsequent Chalcogenation Reactions

Cationic R₂P₅⁺ cage compounds ( 1 ⁺) have been synthesized by the stoichiometric reaction of R₂PCl, GaCl₃ and P₄. The reaction conditions depend on the substituent R. Alkyl‐substituted derivatives ( 1 a – 1 d [GaCl₄]) are best synthesized under solvent‐free conditions, whereas aryl‐substituted derivatives ( 1 e – 1 h [GaCl₄]) are formed in C₆H₅F. All compounds have been prepared on a multi‐gram scale in good to excellent yields and have been fully characterized with an emphasis on ³¹P NMR spectroscopy in solution and single‐crystal structure determination. Subsequent chalcogenation reactions of cations R₂P₅⁺ ( 1 a ⁺, 1 e ⁺) and trication Ph₆P₇³⁺ ( 3 ³⁺) with elemental sulfur (α‐S₈) or grey selenium (Se_grey) yielded a series of unique polyphosphorus–chalcogen cations ( 4 a ⁺, 4 e ⁺, 5 a ⁺, 6 ²⁺ and 7 ²⁺), possessing nortricyclane‐type molecular structures. An in‐depth study of the ³¹P{¹H} and ⁷⁷Se NMR spectroscopic parameters is presented, and correlations between the substitution pattern and the observed structural features have been investigated in detail.     

Cationic Crown Ether Complexes of Germanium(II)

Fit for a king : Cationic complexes of Ge^II can be prepared by using crown ethers to stabilize and protect the germanium center. Three different crown ethers were employed: [12]crown‐4 (see structure, Ge teal, O red, C gray), [15]crown‐5, and [18]crown‐6. The structures of the cationic complexes depend on the cavity size of the crown ether and on the substituent on germanium.

     

Isolation of an Imino‐N‐heterocyclic Carbene/Germanium(0) Adduct: A Mesoionic Germylene Equivalent

An autoionization of germanium dichloride/dioxane complex with an imino‐N‐heterocyclic carbene ligand ( L ) afforded a novel germyliumylidene ion, [( L )GeCl]⁺[GeCl₃]^?, which was fully characterized. Reduction of the germyliumylidene ion with potassium graphite produced a cyclic species [( L )Ge], which can be viewed as both a Ge⁰ species and a mesoionic germylene. X‐ray diffraction analysis and computational studies revealed one of the lone pairs on the Ge atom is involved in the π system on the GeC₂N₂ five‐membered ring. It was also confirmed that the nucleophilic behavior of [( L )Ge] as a two lone‐pair donor.     

A Mechanistic Study on Reactions of Group 13 Diyls LM with Cp*SbX2: From Stibanyl Radicals to Antimony Hydrides

Oxidative addition of Cp*SbX₂ (X=Cl, Br, I; Cp*=C₅Me₅) to group 13 diyls LM (M=Al, Ga, In; L=HC[C(Me)N (Dip)]₂, Dip=2,6-iPr₂C₆H₃) yields elemental antimony (M=Al) or the corresponding stibanylgallanes [L(X)Ga]Sb(X)Cp* (X=Br 1 , I 2 ) and -indanes [L(X)In]Sb(X)Cp* (X=Cl 5 , Br 6 , I 7 ). 1 and 2 react with a second equivalent of LGa to eliminate decamethyl-1,1’-dihydrofulvalene (Cp*₂) and form stibanyl radicals [L(X)Ga]₂Sb ^. (X=Br 3 , I 4 ), whereas analogous reactions of 5 and 6 with LIn selectively yield stibanes [L(X)In]₂SbH (X=Cl 8 , Br 9 ) by elimination of 1,2,3,4-tetramethylfulvene. The reactions are proposed to proceed via formation of [L(X)M]₂SbCp* as reaction intermediate, which is supported by the isolation of [L(Cl)Ga]₂SbCp ( 11 , Cp=C₅H₅). The reaction mechanism was further studied by computational calculations using two different models. The energy values for the Ga- and the In-substituted model systems showing methyl groups instead of the very bulky Dip units are very similar, and in both cases the same products are expected. Homolytic Sb−C bond cleavage yields van der Waals complexes from the as-formed radicals ([L(Cl)M]₂Sb ^. and Cp* ^. ), which can be stabilized by hydrogen atom abstraction to give the corresponding hydrides, whereas the direct formation of Sb hydrides starting from [L(Cl)M]₂SbCp* via concerted β-H elimination is unlikely. The consideration of the bulky Dip units reveals that the amount of the steric overload in the intermediate I determines the product formation (radical vs. hydride).     

Permethylated Disila[2]metallocenophanes of Group 14 and 15 Elements

Permethylated disila[2]metallocenophanes of silicon, germanium, tin, lead, 2 a – d , (tetrelocenophanes) and antimony, 3 a , b , (pnictogenocenophanes) are described. In the case of antimony, a chloro-substituted stibonocenophane, 3 a , as well as cationic stibonocenophanium tetrachloroaluminate and tetraphenylborate salts, 3 b [X] (X=[AlCl₄], [BPh₄]), were synthesized. These represent the first examples of metallocenophanes of any Group 15 element. All compounds were studied in solution and in the solid state. Without exception the ansa-bridge exerts a strong influence on the bending angle of the two Cp-ligands. For disila[2]plumbocenophane, 2 d , its reactivity towards Group 15 halides was probed. Treatment of disila[2]plumbocenophane, 2 d , with two equivalents of phosphorus(III) chloride or arsenic(III) chloride, results in a ring-opening reaction and gives the bis(dihalopnictogenyl)-substituted products, 4 a , b .     

H2 Activation by Non-Transition-Metal Systems: Hydrogenation of Aldimines and Ketimines with LiN(SiMe3)2

In recent years, H₂ activation at non-transition-metal centers has met with increasing attention. Here, a system in which H₂ is activated and transferred to aldimines and ketimines using substoichiometric amounts of lithium bis(trimethylsilyl)amide is reported. Notably, the reaction tolerates the presence of acidic protons in the α-position. Mechanistic investigations indicated that the reaction proceeds via a lithium hydride intermediate as the actual reductant.     

The Synthesis of B2(SIDip)2 and its Reactivity Between the Diboracumulenic and Diborynic Extremes

A new compound with the formula L‐B₂‐L wherein the stabilizing ligand (L) is 1,3‐bis[diisopropylphenyl]‐4,5‐dihydroimidazol‐2‐ylidene (SIDip) has been synthesized, isolated, and characterized. The π‐acidity of the SIDip ligand, intermediate between the relatively non‐acidic IDip (1,3‐bis[diisopropylphenyl]imidazol‐2‐ylidene) ligand and the much more highly acidic CAAC (1‐[2,6‐diisopropylphenyl]‐3,3,5,5‐tetramethylpyrrolidin‐2‐ylidene) ligand, gives rise to a compound with spectroscopic, electrochemical, and structural properties between those of L‐B₂‐L compounds stabilized by CAAC and IDip. Reactions of all three L‐B₂‐L compounds with CO demonstrate the differences caused by their respective ligands, as the π‐acidities of the CAAC and SIDip carbenes enabled the isolation of bis(boraketene) compounds (L(OC)B‐B(CO)L), which could not be isolated from reactions with B₂(IDip)₂. However, only B₂(IDip)₂ and B₂(SIDip)₂ could be converted into bicyclic bis(boralactone) compounds.     

Prediction of Boron–Boron Triple‐Bond Polymers Stabilized by Janus‐Type Bis(N‐heterocyclic) Carbenes

A class of polymeric compounds containing boron–boron triple bonds stabilized by N‐heterocyclic biscarbenes is proposed. Since a triply bonded B₂ is related to its third excited state, the predicted macromolecule would be composed by several units of an electronically excited first‐row homonuclear dimer. Moreover, it is shown that the replacement of biscarbene with N₂ or CO as spacers could change the bonding profile of the boron–boron units to a cumulene‐like structure. Based on these results, different types of diboryne polymers are proposed, which could lead to an unprecedented set of boron materials with distinct physical properties. The novel diboryne macromolecules could be synthesized by the reaction of Janus‐type biscarbenes with tetrabromodiborane, B₂Br₄, and sodium naphthalenide, [Na(C₁₀H₈)], similarly to Braunschweig’s work on the room temperature stable boron–boron triple bond compounds (Science, 2012 , 336, 1420).     

tBuP(NH2)2--a reactive synthon for the synthesis of molecular imidophosphinates of group 13 metals

Reactions of tBuP(NH(2))(2) with Group 13 trialkyls MR(3) (M=Al, Ga, In; R=Me, tBu) were investigated in detail. According to variable-temperature (VT) NMR investigations, the reaction proceeds stepwise with the initial formation of aminophosphane adducts, which subsequently react to give iminophosphorane adducts and finally the heterocyclic metallonitridophosphinates. BP86/TZVPP (DFT) calculations were performed to verify this reaction pathway, to elucidate the influence of the central Group 13 element on the stability of the reaction intermediates and the heterocycles, as well as to assess the thermodynamics of their formation. The relative stability of free and complexed aminophosphane RP(NH(2))(2) and iminophosphorane R(H(2)N)(H)P=NH (adducts) with P(III) and P(V) centers was studied in more detail with DFT and MP2 methods. In addition, the influence of the substituent R was investigated by variation of R from H to Me, tBu, F, and NH(2). In general, the aminophosphane form was found to be favored for the free ligand, however, upon complexation with MR(3) (M=Al, Ga; R=alkyl) both forms are almost equal in energy.     

Reversible,Photoinduced Activation of P4 by Low‐Coordinate Main Group Compounds

Two unique systems based on low‐coordinate main group elements that activate P₄ are shown to quantitatively release the phosphorus cage upon short exposure to UV light. This reactivity marks the first reversible reactivity of P₄, and the germanium system can be cycled 5 times without appreciable loss in activity. Theoretical calculations reveal that the LUMO is antibonding with respect to the main group element–phosphorus bonds and bonding with respect to reforming the P₄ tetrahedron, providing a rationale for this unprecedented activity, and suggesting that the process is tunable based on the substituents.     

P9]+ [Al(OR(F))4)]-, the salt of a homopolyatomic phosphorus cation

Positive at last: The first condensed-phase homopolyatomic phosphorus cation [P(9)](+) was prepared using a combination of the oxidant [NO](+) and weakly coordinating anion, [Al{OC(CF(3))(3)}(4)](-). [P(9)](+) consists of two P(5) cages linked by a phosphonium atom to give a D(2d)-symmetric Zintl cluster. NMR (see picture), Raman, and IR spectroscopy, mass spectrometry, and quantum-chemical calculations confirmed the structure.     

A Versatile Precursor System for Supercritical Fluid Electrodeposition of Main‐Group Materials

For the first time, a versatile electrolyte bath is described that can be used to electrodeposit a wide range of p‐block elements from supercritical difluoromethane (scCH₂F₂). The bath comprises the tetrabutylammonium chlorometallate complex of the element in an electrolyte of 50×10^?3 mol dm^?3 tetrabutylammonium chloride at 17.2 MPa and 358 K. Through the use of anionic ([GaCl₄]^?, [InCl₄]^?, [GeCl₃]^?, [SnCl₃]^?, [SbCl₄]^?, and [BiCl₄]^?) and dianionic ([SeCl₆]^2? and [TeCl₆]^2?) chlorometallate salts, the deposition of elemental Ga, In, Ge, Sn, Sb, Bi, Se, and Te is demonstrated. In all cases, with the exception of gallium, which is a liquid under the deposition conditions, the resulting deposits are characterised by SEM, energy‐dispersive X‐ray analysis, XRD and Raman spectroscopy. An advantage of this electrolyte system is that the reagents are all crystalline solids, reasonably easy to handle and not highly water or oxygen sensitive. The results presented herein significantly broaden the range of materials accessible by electrodeposition from supercritical fluid and open up the future possibility of utilising the full scope of these unique fluids to electrodeposit functional binary or ternary alloys and compounds of these elements.