THF Adduct Research Articles

Alkene Isomerization Catalyzed by a Mn(I) Bisphosphine Borohydride Complex.

An additive-free manganese-catalyzed isomerization of terminal alkenes to internal alkenes is described. This reaction is implementing an inexpensive nonprecious metal catalyst. The most efficient catalyst is the borohydride complex cis-[Mn(dippe)(CO)2(κ2-BH4)]. This catalyst operates at room temperature, with a catalyst loading of 2.5 mol %. A variety of terminal alkenes is effectively and selectively transformed into the respective internal E-alkenes. Preliminary results show chain-walking isomerization at an elevated temperature. Mechanistic studies were carried out, including stoichiometric reactions and in situ NMR analysis. These experiments are flanked by computational studies. Based on these, the catalytic process is initiated by the liberation of "BH3" as a THF adduct. The catalytic process is initiated by double bond insertion into an M-H species, leading to an alkyl metal intermediate, followed by β-hydride elimination at the opposite position to afford the isomerization product.

Synthesis and Structure of Heavy Alkali Metal Pentalenides

AbstractThe solid‐state structures of the first rubidium and caesium pentalenides [Rb(THF)]2[Ph4Pn] and [Cs(THF)]2[Ph4Pn] have been determined by single crystal X‐ray diffraction. Both were found to be polymeric in the solid state through interactions of the cations with the phenyl substituents, in contrast to their lighter group 1 congeners which are monomeric for lithium and sodium, and THF‐bridged for potassium. Both [Rb(THF)]2[Ph4Pn] and [Cs(THF)]2[Ph4Pn] displayed increased η8 coordination, demonstrating a shift towards higher hapticities down the group as previously predicted computationally for the parent M2[Pn] complexes (M=group 1 metal). The solid‐state structures of the polydentate donor adducts [M(DME)x]2[Ph4Pn] (M=Li, x=1; M=Na, x=2) and [M(Me6TREN)]2[Ph4Pn] (M=K, Rb, Cs) were all monomeric and displayed increased metal‐carbon distances and decreased ring slippage values relative to the THF adducts.

Synthesis and Characterization of Bulky 1,3-Diamidopropane Complexes of Group 2 Metals (Be-Sr).

Reaction of lithium 1,3-diamidopropane Li2(TripNCN) (TripNCN=[{(Trip)NCH2}2CH2]2-, Trip=2,4,6-triisopropylphenyl) with BeBr2(OEt2)2 gave the diamido beryllium complex, [(TripNCN)Be(OEt2)]. Deprotonation reactions between the bulkier 1,3-diaminopropane (TCHPNCN)H2 (TCHPNCN=[{(TCHP)NCH2}2CH2]2-, TCHP=2,4,6-tricyclohexylphenyl) and magnesium alkyls afforded the adduct complexes [(TCHPNCN)Mg(OEt2)] and [(TCHPNCN)Mg(THF)2], depending on the reaction conditions employed. Treating [(TCHPNCN)Mg(THF)2] with the N-heterocyclic carbene :C{(MeNCMe)2} (TMC) gave [(TCHPNCN)Mg(TMC)2] via substitution of the THF ligands. Reactions of (ArNCN)H2 (Ar=Trip or TCHP) with Mg{CH2(SiMe3)}2, in the absence of Lewis bases, yielded the N-bridged dimers [{(ArNCN)Mg}2]. Salt metathesis reactions between alkali metal salts M2(TCHPNCN) (M=Li or K) and CaI2 or SrI2 led to the THF adduct compounds [(TCHPNCN)Ca(THF)3] and [(TCHPNCN)Sr(THF)4], the differing number of THF ligands in which is a result of the different sizes of the metals involved. The described complexes hold potential as precursors to kinetically protected, low oxidation state group 2 metal species.

Stoichiometric and Catalytic Reduction of Carbon Dioxide by a Sterically Encumbered Amidinato Magnesium Hydride

AbstractA sterically encumbered dinuclear amidinato magnesium hydride 3 with bridging hydrido ligands was synthesized from the metalation of the corresponding amidine 1 with dibutylmagnesium and subsequent treatment with phenylsilane. This complex reacts stoichiometrically with 1 atm of carbon dioxide at room temperature in tetrahydrofuran (THF) to the corresponding bis(thf) adduct of the dinuclear formate complex 4‐2 thf with bridging formate anions. This complex is stable in THF at 60 °C for more than 16 hours but decomposes into the amidine 1 upon removal of ligated thf ligands. Complex 3 efficiently catalyzes the reduction of carbon dioxide with 9‐BBN, yielding bis(boryl)acetal (R2BO)2CH2, and with silanes H4‐nSiPhn (n=1, 2, and 3). The bis(silyl)acetal is quantitatively accessible for Ph3SiH (n=3) whereas during the reduction of CO2 with hydrogen‐richer silanes (n=1, 2) siloxanes form and methane evolves.

Barium phosphidoboranes and related calcium complexes.

The attempted synthesis of [{Carb}BaPPh2] (1) showed this barium-phosphide and its thf adducts, 1·thf and 1·(thf)2, to be unstable in solution. Our strategy to circumvent the fragility of these compounds involved the use of phosphinoboranes HPPh2·BH3 and HPPh2·B(C6F5)3 instead of HPPh2. This allowed for the synthesis of [{Carb}Ae{PPh2·BH3}] (Ae = Ba, 2; Ca, 3), [{Carb}Ca{(H3B)2PPh2}·(thf)] (4), [{Carb}Ba{PPh2·B(C6F5)3}] (5), [{Carb}Ba{O(B(C6F5)3)CH2CH2CH2CH2PPh2}·thf] (6), [Ba{O(B(C6F5)3)CH2CH2CH2CH2PPh2}2·(thf)1.5] (7) and [Ba{PPh2·B(C6F5)3}2·(thp)2] (8) that were characterised by multinuclear NMR spectroscopy (thp = tetrahydropyran). The molecular structures of 4, 6 and 8 were validated by X-ray diffraction crystallography, which revealed the presence of Ba⋯F stabilizing interactions (ca. 9 kcal mol-1) in the fluorine-containing compounds. Compounds 6 and 7 were obtained upon ring-opening of thf by their respective precursors, 5 and the in situ prepared [Ba{PPh2·B(C6F5)3}2]n. By contrast, thp does not undergo ring-opening under the same conditions but affords clean formation of 8. DFT analysis did not highlight any specific weakness of the Ba-P bond in 1·(thf)2. The instability of this compound is instead thought to stem from the high energy of its HOMO, which contains the non-conjugated P lone pair and features significant nucleophilic reactivity.

Calix[4]pyrrolato-germane-(thf)2: Unlocking the Anti-van't Hoff-Le Bel Reactivity of Germanium(IV) by Ligand Dissociation.

Anti-van't Hoff-Le Bel configured p-block element species possess intrinsically high reactivity and are thus challenging to isolate. Consequently, numerous elements in this configuration, including square-planar germanium(IV), remain unexplored. Herein, we follow a concept to reach anti-van't Hoff-Le Bel reactivity by ligand dissociation from a rigid calix[4]pyrrole germane in its bis(thf) adduct. While the macrocyclic ligand assures square-planar coordination in the uncomplexed form, the labile thf donors provide robustness for isolation on a multigram scale. Unique properties of a low-lying acceptor orbital imparted to germanium(IV) can be verified, e.g., by isolating an elusive anionic hydrido germanate and exploiting it for challenging bond activations. Aldehydes, water, alcohol, and a CN triple bond are activated for the first time by germanium-ligand cooperativity. Unexpected behaviors against fluoride ion donors disclose critical interferences of a putative redox-coupled fluoride ion transfer during the experimental determination of Lewis acidity. Overall, we showcase how ligand lability grants access to the uncharted chemistry of anti-van't Hoff-Le Bel germanium(IV) and line up this element as a member in the emerging class of structurally constrained p-block elements.

Reduction of Nitrous Oxide and Binding of Carbon Dioxide by Acenaphthene-1,2-diimine Aluminum Compounds

The reaction of dialane [(dpp-bian)Al–Al(dpp-bian)] (1) (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with N2O results in the formation of oxide [(dpp-bian)Al(μ2-O)2Al(dpp-bian)] (2). The reaction of the thf adduct of 1, [(dpp-bian)(thf)Al–Al(thf)(dpp-bian)] (3), with N2O affords oxo-bridged [(dpp-bian)Al(thf)(μ-O)Al(thf)(dpp-bian)] (4). The addition of carbon dioxide to compound 2 leads to the formation of carbonate [(dpp-bian)Al(μ-O)(μ-CO3)Al(dpp-bian)] (5). Diamagnetic derivatives have been characterized by 1H NMR spectroscopy and paramagnetic compounds by electron paramagnetic resonance spectroscopy; their molecular structures have been established by single-crystal X-ray analysis.

A Hydride-Substituted Homoleptic Silylborate: How Similar is it to its Diborane(6)-Dianion Isostere?

The B-nucleophilic 9H-9-borafluorene dianion reacts with 9-chloro-9-silafluorene to afford air- and moisture-stable silylborate salts M[Ar2 (H)B-Si(H)Ar2 ] (M[HBSiH], M=Li, Na). Li[HBSiH] and Me3 SiCl give the B-pyridine adduct Ar2 (py)B-Si(H)Ar2 ((py)BSiH) or the chlorosilane Li[Ar2 (H)B-Si(Cl)Ar2 ] (Li[HBSiCl]) in C6 H6 -pyridine or THF. In both cases, the first step is H- abstraction at the B center. The resulting free borane subsequently binds a py or thf ligand. While the py adduct is stable at room temperature, the thf adduct undergoes a 1,2-H shift via the cyclic B(μ-H)Si intermediate BHSi, which is afterwards attacked at the Si atom by a Cl- ion to give Li[HBSiCl]. DFT calculations were employed to support the proposed reaction mechanism and to characterize the electronic structure of BHSi. Treatment of Li[HBSiCl] with the N-heterocyclic carbene IMe introduces the neutral donor at the Si atom and leads to Ar2 (H)B-Si(IMe)Ar2 (HBSi(IMe)), a donor-acceptor-stabilized silylene.

Synthesis, Characterization, and Structural Analysis of AM[Al(NONDipp)(H)(SiH2Ph)] (AM = Li, Na, K, Rb, Cs) Compounds, Made Via Oxidative Addition of Phenylsilane to Alkali Metal Aluminyls.

We report the oxidative addition of phenylsilane to the complete series of alkali metal (AM) aluminyls [AM{Al(NONDipp)}]2 (AM = Li, Na, K, Rb, and Cs). Crystalline products (1-AM) have been isolated as ether or THF adducts, [AM(L)n][Al(NONDipp)(H)(SiH2Ph)] (AM = Li, Na, K, Rb, L = Et2O, n = 1; AM = Cs, L = THF, n = 2). Further to this series, the novel rubidium rubidiate, [{Rb(THF)4}2(Rb{Al(NONDipp)(H)(SiH2Ph)}2)]+ [Rb{Al(NONDipp)(H)(SiH2Ph)}2]-, was isolated during an attempted recrystallization of Rb[Al(NONDipp)(H)(SiH2Ph)] from a hexane/THF mixture. Structural and spectroscopic characterizations of the series 1-AM confirm the presence of μ-hydrides that bridge the aluminum and alkali metals (AM), with multiple stabilizing AM···π(arene) interactions to either the Dipp- or Ph-substituents. These products form a complete series of soluble, alkali metal (hydrido) aluminates that present a platform for further reactivity studies.

Synthesis and Complexation Study of New Aminoalkynyl−amidinate Ligands

AbstractThe current library of amidinate ligands has been extended by the synthesis of two novel dimethylamino‐substituted alkynylamidinate anions of the composition [Me2N−CH2−C≡C−C(NR)2]−(R =iPr, cyclohexyl (Cy)). The unsolvated lithium derivatives Li[Me2N−CH2−C≡C−C(NR)2] (1: R =iPr,2: R = Cy) were obtained in good yields by treatment ofin situ‐prepared Me2N−CH2−C≡C−Li with the respective carbodiimides, R−N=C=N−R. Recrystallization of1and2from THF afforded the crystalline THF adducts Li[Me2N−CH2−C≡C−C(NR)2] ⋅ nTHF (1 a: R =iPr,n=1;2 a: R = Cy,n=1.5). Precursor2was subsequently used to study initial complexation reactions with selected di‐ and trivalent transition metals. The dark red homoleptic vanadium(III) tris(alkynylamidinate) complex V[Me2N−CH2−C≡C−C(NCy)2]3(3) was prepared by reaction of VCl3(THF)3with 3 equiv. of2(75 % yield). A salt‐metathesis reaction of2with anhydrous FeCl2in a molar ratio of 2 : 1 afforded the dinuclear homoleptic iron(II) alkynylamidinate complex Fe2[Me2N−CH2−C≡C−C(NCy)2]4(4) in 69 % isolated yield. Similarly, treatment of Mo2(OAc)4with 3 or 4 equiv. of2provided the dinuclear, heteroleptic molybdenum(II) amidinate complex Mo2(OAc)[Me2N−CH2−C≡C−C(NCy)2]3(5; yellow crystals, 50 % isolated yield). The cyclohexyl‐substituted title compounds2 a,4, and5were structurally characterized through single‐crystal X‐ray diffraction studies.

Cationic Nickel d9‐Metalloradicals [Ni(NHC)2]+

AbstractA series of five new homoleptic, linear nickel d9‐complexes of the type [NiI(NHC)2]+ is reported. Starting from the literature known Ni(0) complexes [Ni(Mes2Im)2] 1, [Ni(Mes2ImH2)2] 2, [Ni(Dipp2Im)2] 3, [Ni(Dipp2ImH2)2] 4 and [Ni(cAACMe)2] 5 (Mes2Im=1,3‐bis(2,4,6‐trimethylphenyl)‐imidazolin‐2‐ylidene, Mes2ImH2=1,3‐bis(2,4,6‐trimethylphenyl)‐imidazolidin‐2‐ylidene, Dipp2Im=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene, Dipp2ImH2=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolidin‐2‐ylidene, cAACMe=1‐(2,6‐diisopropylphenyl)‐3,3,5,5‐tetramethylpyrrolidin‐2‐yliden), their oxidized Ni(I) analogues [NiI(Mes2Im)2][BPh4] 1+, [NiI(Mes2ImH2)2][BPh4] 2+, [NiI(Dipp2Im)2][BPh4] 3+, [NiI(Dipp2ImH2)2][BPh4] 4+ and [NiI(cAACMe)2][BPh4] 5+ were synthesized by one‐electron oxidation with ferrocenium tetraphenyl‐borate. The complexes 1+–5+ were fully characterized including X‐ray structure analysis. The complex cations reveal linear geometries in the solid state and NMR spectra with extremely broad, paramagnetically shifted resonances. DFT calculations predicted an orbitally degenerate ground state leading to large magnetic anisotropy, which was verified by EPR measurements in solution and on solid samples. The magnetic anisotropy of the complexes is highly dependent from the steric protection of the metal atom, which results in a noticeable decrease of the g‐tensor anisotropy for the N‐Mes substituted complexes 1+ and 2+ in solution due to the formation of T‐shaped THF adducts.

N‐Heterocyclic Carbene and Cyclic (Alkyl)(amino)carbene Adducts of Germanium(IV) and Tin(IV) Chlorides and Organyl Chlorides

AbstractA study on the reactivity of N‐heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene cAACMe with selected germanium(IV) and tin(IV) chlorides and organyl chlorides is presented. The reactions of the NHCs Me2ImMe, iPr2ImMe and Dipp2Im with the methyl chlorides ECl2Me2 afforded the adducts NHC ⋅ ECl2Me2 (E=Ge (1), Sn (2)), NHC=Me2ImMe (a), iPr2ImMe (b), Dipp2Im (c)). The reaction of Me2ImMe with GeCl4 led to isolation of Me2ImMe ⋅ GeCl4 (3), the reaction of iPr2ImMe with SnCl4 in THF afforded the THF adduct iPr2ImMe ⋅ SnCl4 ⋅ THF (4). Dipp2Im ⋅ GeCl2Me2 (1 c) isomerized into the backbone coordinated imidazolium salt [aDipp2Im ⋅ GeClMe2][Cl] (5) upon thermal treatment. The reactions of cAACMe with (i) ECl2R2 (E=Ge, Sn) gave the adducts cAACMe ⋅ ECl2R2 (R=Me: E=Ge (6); Sn (7); Ph: E=Ge (8)), with (ii) GeClMe3 and GeCl4 the salts [cAACMe ⋅ GeMe3][Cl] (9) and [cAACMeCl][GeCl3] (10), and (iii) with SnCl4 the salt [cAACMeCl][SnCl3] (11) and the adduct cAACMe ⋅ SnCl4 (12). Reduction of 2 a with KC8 afforded the NHC‐stabilized stannylene Me2ImMe ⋅ SnMe2 13, reduction of 7 with either KC8 or 1,4‐bis‐(trimethylsilyl)‐1,4‐dihydropyrazin in the presence of SnCl2Me2 yielded cAACMe ⋅ SnMe2 ⋅ SnMe2Cl2 (14).

Synthesis and Structure of a New Bulky Hybrid Scorpionate/Cyclopentadienyl Ligand and its Lithium Complex

AbstractThe reaction of 5‐(1‐adamantyl)‐3‐methyl‐1H‐pyrazole with dibromomethane yields a product mixture of bis(3‐adamantyl‐5‐methylpyrazolyl)methane (H2C(PzAd,Me)2, 2 a), (3‐adamantyl‐5‐methylpyrazolyl)‐(3‐methyl‐5‐adamantylpyrazolyl)methane ((H2C(PzAd,Me)(PzMe,Ad), 2 b) and bis(3‐methyl‐5‐adamantylpyrazolyl)methane (H2C(PzMe,Ad)2, 2 c). Lithiation of sterically congested H2C(PzAd,Me)2 (2 a) and subsequent addition of diphenylfulvene yields lithium 1,1‐bis(3‐adamantyl‐5‐methylpyrazolyl)‐2,2‐diphenyl‐2‐ethyl‐cyclopentadienide, [(thf)Li{Cp−CPh2−CHPzAd,Me}] (3) which is unable to form a thf adduct but can be hydrolyzed to H5C5−CPh2−CHPzAd,Me (4). Adamantyl groups in 5‐position of bis(pyrazolyl)methane, i. e. 2 b and 2 c, prohibit formation of a fulvene adduct. For comparison reasons, [{H5C5−CPh2−CHPzMe2}LiI] (1 b) has been prepared via protolysis of (thf)lithium 1,1‐bis(3,5‐dimethylpyrazolyl)‐2,2‐diphenyl‐2‐ethyl‐cyclopentadienide, [(thf)Li{Cp−CPh2−CHPzMe2}] (1 a), in the presence of calcium iodide.

Replacement of the Common Chromium Source CrCl3(thf)3 with Well-Defined [CrCl2(μ-Cl)(thf)2]2.

CrCl3(thf)3 is a common starting material in the synthesis of organometallic and coordination compounds of Cr. Deposited as an irregular solid with no possibility of recrystallization, it is not a purity guaranteed chemical, causing problems in some cases. In this work, we disclose a well-defined form of the THF adduct of CrCl3 ([CrCl2(μ-Cl)(thf)2]2), a crystalline solid, that enables structure determination by X-ray crystallography. The EA data and XRD pattern of the bulk agreed with the revealed structure. Moreover, its preparation procedure is facile: evacuation of CrCl3·6H2O at 100 °C, treatment with 6 equivalents of Me3SiCl in a minimal amount of THF, and crystallization from CH2Cl2. The ethylene tetramerization catalyst [iPrN{P(C6H4-p-Si(nBu)3)2}2CrCl2]+[B(C6F5)4]− prepared using well-defined [CrCl2(μ-Cl)(thf)2]2 as a starting material exhibited a reliably high activity (6600 kg/g-Cr/h; 1-octene selectivity at 40 °C, 75%), while that of the one prepared using the impure CrCl3(thf)3 was inconsistent and relatively low (~3000 kg/g-Cr/h). By using well-defined [CrCl2(μ-Cl)(thf)2]2 as a Cr source, single crystals of [(CH3CN)4CrCl2]+[B(C6F5)4]− and [{Et(Cl)Al(N(iPr)2)2}Cr(μ-Cl)]2 were obtained, allowing structure determination by X-ray crystallography, which had been unsuccessful when the previously known CrCl3(thf)3 was used as the Cr source.

Synthesis and Characterization of Strontium N,N-Dimethylaminodiboranates as Possible Chemical Vapor Deposition Precursors.

The reaction of SrBr2 with 2 equiv of sodium N,N-dimethylaminodiboranate (DMADB; Na(H3BNMe2BH3)) in Et2O at 0 °C followed by crystallization and drying under vacuum gives the unsolvated strontium compound Sr(H3BNMe2BH3)2 (1). Before the vacuum-drying step, the colorless crystals obtained by crystallization consist of the diethyl ether adduct Sr(H3BNMe2BH3)2(Et2O)2 (2). If the reaction of SrBr2 with 2 equiv of Na(H3BNMe2BH3) is carried out in the more strongly coordinating solvent thf, the solvate Sr(H3BNMe2BH3)2(thf)3 (3) is obtained. Treating the thf adduct 3 with 1,2-dimethoxyethane (dme), bis(2-methoxyethyl) ether (diglyme), or N,N,N',N'-tetramethylethylenediamine (tmeda) in thf affords the new compounds Sr(H3BNMe2BH3)2(dme)2 (4), Sr(H3BNMe2BH3)2(diglyme) (5), and Sr(H3BNMe2BH3)2(tmeda) (6), respectively, in greater than 60% yields. Treatment of 3 with 2 equiv of the crown ether 12-crown-4 affords the charge-separated salt [Sr(H3BNMe2BH3)(12-crown-4)2][H3BNMe2BH3] (7). Crystal structures of all the Lewis base adducts are described. Compounds 2-6 all possess chelating κ2-BH3NMe2BH3-κ2 groups, in which two hydrogen atoms on each boron center are bound to strontium. Compound 6 is dinuclear because each metal atom is also coordinated to one hydrogen atom on a BH3NMe2BH3- ligand that chelates to the neighboring metal center. Compound 7 possesses an unusual κ1-BH3NMe2BH3- group owing to the near-complete encapsulation of the Sr atom by two 12-crown-4 molecules; the other BH3NMe2BH3- anion is a charge-separated counterion. When they are heated, the diglyme and tmeda compounds 5 and 6 melt without decomposition and can be sublimed readily under reduced pressure (1 Torr) at 120 °C. The diglyme and tmeda adducts are some of the most volatile strontium compounds known and are promising candidates as CVD precursors for the growth of strontium-containing thin films.

Synthesis of Dinuclear Mo-Fe Hydride Complexes and Catalytic Silylation of N2.

Two transition-metal atoms bridged by hydrides may represent a useful structural motif for N2 activation by molecular complexes and the enzyme active site. In this study, dinuclear MoIV -FeII complexes with bridging hydrides, CpR Mo(PMe3 )(H)(μ-H)3 FeCp* (2 a; CpR =Cp*=C5 Me5 , 2 b; CpR =C5 Me4 H), were synthesized via deprotonation of CpR Mo(PMe3 )H5 (1 a; CpR =Cp*, 1 b; CpR =C5 Me4 H) by Cp*FeN(SiMe3 )2 , and they were characterized by spectroscopy and crystallography. These Mo-Fe complexes reveal the shortest Mo-Fe distances ever reported (2.4005(3) Å for 2 a and 2.3952(3) Å for 2 b), and the Mo-Fe interactions were analyzed by computational studies. Removal of the terminal Mo-H hydride in 2 a-2 b by [Ph3 C]+ in THF led to the formation of cationic THF adducts [CpR Mo(PMe3 )(THF)(μ-H)3 FeCp*]+ (3 a; CpR =Cp*, 3 b; CpR =C5 Me4 H). Further reaction of 3 a with LiPPh2 gave rise to a phosphido-bridged complex Cp*Mo(PMe3 )(μ-H)(μ-PPh2 )FeCp* (4). A series of Mo-Fe complexes were subjected to catalytic silylation of N2 in the presence of Na and Me3 SiCl, furnishing up to 129±20 equiv of N(SiMe3 )3 per molecule of 2 b. Mechanism of the catalytic cycle was analyzed by DFT calculations.

The 9H-9-Borafluorene Dianion: A Surrogate for Elusive Diarylboryl Anion Nucleophiles.

Double reduction of the THF adduct of 9H‐9‐borafluorene (1⋅THF) with excess alkali metal affords the dianion salts M2[1] in essentially quantitative yields (M=Li–K). Even though the added charge is stabilized through π delocalization, [1]2− acts as a formal boron nucleophile toward organoboron (1⋅THF) and tetrel halide electrophiles (MeCl, Et3SiCl, Me3SnCl) to form B−B/C/Si/Sn bonds. The substrate dependence of open‐shell versus closed‐shell pathways has been investigated.

Activation of Protic, Hydridic and Apolar E-H Bonds by a Boryl-Substituted GeII Cation.

The synthesis of a boryl-substituted germanium(II) cation, [Ge{B(NDippCH)2 }(IPrMe)]+ , (Dipp=2,6-diisopropylphenyl) featuring a supporting N-heterocyclic carbene (NHC) donor, has been explored through chloride abstraction from the corresponding (boryl)(NHC)GeCl precursor. Crystallographic studies in the solid state and UV/Vis spectra in fluorobenzene solution show that this species dimerizes under such conditions to give [(IPrMe){(HCNDipp)2 B}Ge=Ge{B(NDippCH)2 }(IPrMe)]2+ (IPrMe = 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene), which can be viewed as an imidazolium-functionalized digermene. The dimer is cleaved in the presence of donor solvents such as [D8 ]thf or [D5 ]pyridine, to give monomeric adducts of the type [Ge{B(NDippCH)2 }(IPrMe)(L)]+ . In the case of the thf adduct, the additional donor is shown to be sufficiently labile that it can act as a convenient in situ source of the monomeric complex [Ge{B(NDippCH)2 }(IPrMe)]+ for oxidative bond-activation chemistry. Thus, [Ge{B(NDippCH)2 }(IPrMe)(thf)]+ reacts with silanes and dihydrogen, leading to the formation of GeIV products, whereas the cleavage of the N-H bond in ammonia ultimately yields products containing C-H and B-N bonds. The facile reactivity observed in E-H bond activation is in line with the very small calculated HOMO-LUMO gap (132 kJ mol-1 ).

Synthesis and Characterization of Neutral and Cationic Magnesium Complexes Supported by NHC Ligands

A series of neutral N-heterocyclic carbene (NHC) magnesium alkyl complexes was synthesized by reaction of IMes (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and IPr (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with Grignard reagents. In the presence of THF, the mononuclear species [Mg(IMes)(R)(Br)(THF)] (1, R = Me; 2, R = Et) and [Mg(IPr)(R)(Br)(THF)] (3, R = Me; 4, R = Et) were isolated. Complex 4 was further methylated to afford the Mg–THF adduct [Mg(IPr)(Me)2(THF)] (5), which crystallizes as the dimer [{(Mg(IPr)(Me)}2(μ-Me)2] (5′), thus evidencing the labile THF coordination in these systems. In contrast, in the presence of Et2O, the dinuclear Mg(II) species [{(Mg(NHC)(Br)}2(μ-Me)2] (6, NHC = IMes; 7, NHC = IPr), [{(Mg(IMes)(Ph)}2(μ-Br)2] (8), [{(Mg(IMes)(CH2Ph)}2(μ-Cl)2] (9), and [{(Mg(IPr)(Ph)}2(μ-Br)2] (10) were isolated and characterized. The protonolysis reaction between the protio ligand [IMes-H]Cl and EtMgBr afforded the Mg(II) dihalido dimer [{(Mg(IMes)(Br)}2(μ-Cl)2] (11...

Bis(trimethylsilyl)amide complexes of s-block metals with bidentate ether and amine ligands.

The synthesis of the bistrimethylsilylamide complexes of alkali and alkaline-earth metals with bidentate ether and amine bases 1,2-bis(dimethylamino)ethane (tetramethylethylenediamine, tmeda), dimethyl-methoxyethylamine (dmmea), and 1,2-dimethoxyethane (dme) succeeds via addition of these bases to coligand-free complexes or via ligand exchange of thf adducts. The lithium and sodium complexes are mononuclear (exceptions: [(dme)LiN(SiMe3)2]2 and [(tmeda)NaN(SiMe3)2]2) whereas the heavier congeners form dinuclear compounds with central four-membered M2N2 rings. The alkaline-earth metal complexes crystallize as mononuclear complexes i.e. as [(L)M{N(SiMe3)2}2] with four-coordinate metal centers or as [(L)2M{N(SiMe3)2}2] with six-coordinate metal atoms. Intramolecular steric repulsion leads to distortions such as an asymmetric coordination of L and/or significantly different proximal and distal M-N-Si bond angles.