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Diphenylformamide 1 and bisformamide 9 are shown to be safe reservoirs and sources of CO. Their perfectly selective decarbonylations are achieved in solution at room temperature with potassium and cesium diarylamide catalysts. 1 is obtained in excellent yields directly from triethylammonium formate, which may be the product of CO 2 scrubbing with NEt 3 and catalytic hydrogenation. 1 thus represents a key intermediate in a low-temperature rWGS reaction sequence. Moreover, solvent-free decarbonylations of 1 may be run either in the melt at 70 °C or with 9 even in the solid state at 88 °C with improved atom economy. These simple and practical transition-metal-free decarbonylations afford ultra-pure (i. e. dry and solvent-free) CO at moderate temperatures and the diarylamines byproducts are recycled as pure compounds. In the absence of catalysts, diarylformamides 1 and 9 are long-term stable at >200 °C. DFT-calculations indicate a reaction pathway with a rate-determining deprotonation of Ph 2 NC(O)H and barrier-free CO elimination from Ph 2 NC(O) - ., (© 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

Alcohols can be produced by nucleophilic addition at the C=O functional group of ketones or aldehydes. Such C-C bond formations generally proceed smoothly and selective. In contrast, nucleophilic addition at carbon monoxide is considerably more complex and unselective due to the instability of polar metal acyl intermediates. Herein, we report a magnesium alkyl complex, stabilised with a dipyrromethenide ligand, and its reactivity with CO 2 and CO. Whilst the reaction with CO 2 gave the expected carboxylate, reaction with CO took a surprising course, resulting in an alkoxide by formation of three new C-C bonds in a single reaction. An intertwined experimental and computational approach sheds light on the unusual reactivity of a carbene intermediate., (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)

Attempts to create a novel Mg-Be bond by reaction of [( DIPeP BDI*)MgNa] 2 with Be[N(SiMe 3 ) 2 ] 2 failed; DIPeP BDI*=HC[(tBu)C=N(DIPeP)] 2 , DIPeP=2,6-Et 2 C-phenyl. Even at elevated temperatures, no conversion was observed. This is likely caused by strong steric shielding of the Be center. A similar reaction with the more open Cp*BeCl gave in quantitative yield ( DIPeP BDI*)MgBeCp* (1). The crystal structure shows a Mg-Be bond of 2.469(4) Å. Homolytic cleavage of the Mg-Be bond requires ΔH=69.6 kcal mol -1 (cf. CpBe-BeCp 69.0 kcal mol -1 and ( DIPP BDI)Mg-Mg( DIPP BDI) 55.8 kcal mol -1 ). Natural-Population-Analysis (NPA) shows fragment charges: ( DIPeP BDI*)Mg +0.27/BeCp* -0.27. The very low NPA charge on Be (+0.62) compared to Mg (+1.21) and the strongly upfield 9 Be NMR signal at -23.7 ppm are in line with considerable electron density on Be and the formal oxidation state assignment of Mg II -Be 0 . Despite this Mg δ+ -Be δ- polarity, 1 is extremely thermally stable and unreactive towards H 2 , CO, N 2 , cyclohexene and carbodiimide. It reacted with benzophenone, azobenzene, phenyl acetylene, CO 2 and CS 2 . Reaction with 1-adamantyl azide led to reductive coupling and formation of an N 6 -chain. The azide reagent also inserted in the Cp*-Be bond. The inertness of 1 is likely due to bulky ligands protecting the Mg-Be unit., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Inverse sandwich complexes of Yb and Sm stabilized by a bulky β-diketiminate (BDI) ligand have been prepared: (BDI)Ln(η 6 ,η 6 -C 6 H 6 )Ln(BDI); Ln=lanthanide. Coordinated benzene ligands can be neutral, di-anionic or, often controversially discussed, even tetra-anionic. The formal charge on benzene is correlated to assignment of the metal oxidation state which generally poses a problem. Herein, we take advantage of the structural similarities found when comparing Ca II with Yb II , and Sr II with Sm II complexes. In this work, we found an excellent overlap of the Ca/Yb inverse sandwich structures but a striking difference for the Sr/Sm pair. The much shorter Sm-N and Sm-C 6 H 6 distances are strong evidence for a Sm III -benzene -4 -Sm III assignment. This was further supported by NMR spectroscopy, magnetic susceptibility, reactivity and comprehensive computational investigation., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The chemistry of extremely bulky amide ligands is troubled by difficulties in deprotonation of the parent amine. As an alternative route to superbulky amide reagents, the addition of polar reagents to a sila-imine has been investigated. Attempts to synthesize the superbulky amide anion (tBu 3 Si) 2 N - by addition of tBuLi to tBu 2 Si=N(SitBu 3 ) failed and gave tBu 3 Si(tBu 2 HSi)NLi and isobutene. Reaction of the sila-imine with KOtBu successfully led to tBu 3 Si[tBu 2 (tBuO)Si]NK which crystallized as a separated ion-pair. Reaction with the slightly bulkier KOAd (Ad=1-adamantyl) led in presence of THF to ether ring-opening. Reaction with tBuOH gave tBu 3 Si[tBu 2 (tBuO)Si]NH but this amine cannot be easily deprotonated. Reaction with (BDI*)MgnBu in presence of THF gave (BDI*)Mg +  ⋅ (THF) 2 and the non-coordinating anion tBu 3 Si[tBu 2 (nBu)Si]N - ; BDI*=ß-diketiminate ligand HC[C(tBu)N-DIPP] 2 , DIPP=2,6-diisopropylphenyl. Reaction of Mg(nBu) 2 with tBu 2 Si=N(SitBu 3 ) led to a Mg complex with one amide ligand: tBu 3 Si[tBu 2 (nBu)Si]N - . The other superbulky amide anion isomerized by internal deprotonation of a tBu-substituent to give a primary carbanion that is also coordinated to Mg. Although the amide-to-carbanion isomerization is highly contrathermodynamic, it allows for coordination of both anions to a single Mg center. The new bulky amides are rare cases of halogen-free weakly coordinating anions., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

A hydrocarbon-soluble barium anthracene complex was prepared by means of metal vapour synthesis. Reaction of 9,10-bis(trimethylsilyl)anthracene (Anth'') with barium vapour gave deep purple Ba(Anth'') which after extraction with diethyl ether crystallised as the cyclic octamer [Ba(Anth'')⋅Et 2 O] 8 . Dissolution in benzene or toluene led to replacement of the Et 2 O ligand with a softer arene ligand and isolation of Ba(Anth'')⋅arene. Diffusion ordered spectroscopy (DOSY NMR ) measurements in benzene-d 6 indicate solution species with a molecular weight that equals a trimeric constitution. Natural population analysis (NPA) assigned charges of +1.70 and -1.70 to Ba and Anth'', respectively, relating to highly ionic Ba 2+ /Anth'' 2- bonding. Preliminary reactivity studies with air, Ph 2 C=NPh, or H 2 show that the complex reacts as a Ba 0 synthon by release of neutral Anth''. This soluble molecular Ba 0 /Ba II redox synthon provides new routes for the syntheses of barium complexes under mild conditions., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Alkenes that normally do not react with LiAlH 4 (3-hexene, cyclohexene, 1-Me-cyclohexene), can be reduced to the corresponding alkanes by a mixture of LiAlH 4 and Fe 0 (the iron was activated by Metal-Vapour-Synthesis). This alkene-to-alkane conversion with a stoichiometric quantity of LiAlH 4 /Fe 0 does not need quenching with water or acids, implying that both H's originate from LiAlH 4 . The LiAlH 4 /Fe 0 combination is also a remarkably potent cooperative catalyst for hydrogenation of multi-substituted alkenes and benzene or toluene. An induction period of circa two hours and the minimally required temperature of 120 °C, suggests that the actual catalyst is a combination of Fe 0 and the decomposition product of LiAlH 4 (LiH and Al 0 ). A thermally pre-activated LiAlH 4 /Fe 0 catalyst did not need an induction time and is also active at room temperature and 1 bar H 2 . A combination of AliBu 3 and Fe 0 is an even more active hydrogenation catalyst. Without pre-activation, tetra-substituted alkenes like Me 2 C=CMe 2 and toluene could be fully hydrogenated., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Complex [( DIPeP BDI)Ca] 2 (C 6 H 6 ), with a C 6 H 6 2- dianion bridging two Ca 2+ ions, reacts with benzene to yield [( DIPeP BDI)Ca] 2 (biphenyl) with a bridging biphenyl 2- dianion ( DIPeP BDI=HC[C(Me)N-DIPeP] 2 ; DIPeP=2,6-CH(Et) 2 -phenyl). The biphenyl complex was also prepared by reacting [( DIPeP BDI)Ca] 2 (C 6 H 6 ) with biphenyl or by reduction of [( DIPeP BDI)CaI] 2 with KC 8 in presence of biphenyl. Benzene-benzene coupling was also observed when the deep purple product of ball-milling [( DIPP BDI)CaI(THF)] 2 with K/KI was extracted with benzene (DIPP=2,6-CH(Me) 2 -phenyl) giving crystalline [( DIPP BDI)Ca(THF)] 2 (biphenyl) (52 % yield). Reduction of [( DIPeP BDI)SrI] 2 with KC 8 gave highly labile [( DIPeP BDI)Sr] 2 (C 6 H 6 ) as a black powder (61 % yield) which reacts rapidly and selectively with benzene to [( DIPeP BDI)Sr] 2 (biphenyl). DFT calculations show that the most likely route for biphenyl formation is a pathway in which the C 6 H 6 2- dianion attacks neutral benzene. This is facilitated by metal-benzene coordination., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

In order to isolate a monometallic Mg radical, the precursor (Am)MgI⋅(CAAC) (1) was prepared (Am=tBuC(N-DIPP) 2 , DIPP=2,6-diisopropylphenyl, CAAC=cyclic (alkyl)(amino)carbene). Reduction of a solution of 1 in toluene with the reducing agent K/KI led to formation of a deep purple complex that rapidly decomposed. Ball-milling of 1 with K/KI gave the low-valent Mg I complex (Am)Mg⋅(CAAC) (2) which after rapid extraction with pentane and crystallization was isolated in 15 % yield. Although a benzene solution of 2 decomposes rapidly to give Mg(Am) 2 (3) and unidentified products, the radical is stable in the solid state. Its crystal structure shows planar trigonal coordination at Mg. The extremely short Mg-C distance of 2.056(2) Å indicates strong Mg-CAAC bonding. Calculations and EPR measurements show that most of the spin density is in a π* orbital located at the C-N bond in CAAC, leading to significant C-N bond elongation. This is supported by calculated NPA charges in 2: Mg +1.73, CAAC -0.82. Similar metal-to-CAAC charge transfer was calculated for M 0 (CAAC) 2 and [M I (CAAC) 2 + ] (M=Be, Mg, Ca) complexes in which the metal charges range from +1.50 to +1.70. Although the spin density of the radical is mainly located at the CAAC ligand, complex 2 reacts as a low-valent Mg I complex: reaction with a I 2 solution in toluene gave (Am)MgI⋅(CAAC) (1) as the major product., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Low-valent ( Me BDI)Al and ( Me BDI)Ga and highly Lewis acidic cations in [( tBu BDI)M + ⋅C 6 H 6 ][(B(C 6 F 5 ) 4 - ] (M=Mg or Zn, Me BDI=HC[C(Me)N-DIPP] 2 , tBu BDI=HC[C(tBu)N-DIPP] 2 , DIPP=2,6-diisopropylphenyl) react to heterobimetallic cations [( tBu BDI)Mg-Al( Me BDI) + ], [( tBu BDI)Mg-Ga( Me BDI) + ] and [( tBu BDI)Zn-Ga( Me BDI) + ]. These cations feature long Mg-Al (or Ga) bonds while the Zn-Ga bond is short. The [( tBu BDI)Zn-Al( Me BDI) + ] cation was not formed. Combined AIM and charge calculations suggest that the metal-metal bonds to Zn are considerably more covalent, whereas those to Mg should be described as weak Al I (or Ga I )→Mg 2+ donor bonds. Failure to isolate the Zn-Al combination originates from cleavage of the C-F bond in the solvent fluorobenzene to give ( tBu BDI)ZnPh and ( Me BDI)AlF + which is extremely Lewis acidic and was not observed, but ( Me BDI)Al(F)-(μ-F)-(F)Al( Me BDI) + was verified by X-ray diffraction. DFT calculations show that the remarkably facile C-F bond cleavage follows a dearomatization/rearomatization route., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Strongly Lewis acidic cationic aluminium complexes, stabilized by β-diketiminate (BDI) ligands and free of Lewis bases, have been prepared as their B(C 6 F 5 ) 4 - salts and were investigated for catalytic activity in imine hydrogenation. The backbone (R1) and N (R2) substituents on the R1,R2 BDI ligand ( R1,R2 BDI=HC[C(R1)N(R2)] 2 ) influence sterics and Lewis acidity. Ligand bulk increases along the row Me,DIPP BDI< Me,DIPeP BDI≈ tBu,DIPP BDI< tBu,DIPeP BDI; DIPP=2,6-C(H)Me 2 -phenyl, DIPeP=2,6-C(H)Et 2 -phenyl. The Gutmann-Beckett test showed acceptor numbers of: ( tBu,DIPP BDI)AlMe + 85.6, ( tBu,DIPeP BDI)AlMe + 85.9, ( Me,DIPP BDI)AlMe + 89.7, ( Me,DIPeP BDI)AlMe + 90.8, ( Me,DIPP BDI)AlH + 95.3. Steric and electronic factors need to be balanced for catalytic activity in imine hydrogenation. Open, highly Lewis acidic, cations strongly coordinate imine rendering it inactive as a Frustrated Lewis Pair (FLP). The bulkiest cations do not coordinate imine but its combination is also not an active catalyst. The cation ( tBu,DIPP BDI)AlMe + shows the best catalytic activity for various imines and is also an active catalyst for the Tishchenko reaction of benzaldehyde to benzylbenzoate. DFT calculations on the mechanism of imine hydrogenation catalysed by cationic Al complexes reveal two interconnected catalytic cycles operating in concert. Hydrogen is activated either by FLP reactivity of an Al⋅⋅⋅imine couple or, after formation of significant quantities of amine, by reaction with an Al⋅⋅⋅amine couple. The latter autocatalytic Al⋅⋅⋅amine cycle is energetically favoured., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Ba metal was activated by evaporation and cocondensation with heptane. This black powder is a highly active hydrogenation catalyst for the reduction of a variety of unactivated (non-conjugated) mono-, di- and tri-substituted alkenes, tetraphenylethylene, benzene, a number of polycyclic aromatic hydrocarbons, aldimines, ketimines and various pyridines. The performance of metallic Ba in hydrogenation catalysis tops that of the hitherto most active molecular group 2 metal catalysts. Depending on the substrate, two different catalytic cycles are proposed. A: a classical metal hydride cycle and B: the Ba metal cycle. The latter is proposed for substrates that are easily reduced by Ba 0 , that is, conjugated alkenes, alkynes, annulated rings, imines and pyridines. In addition, a mechanism in which Ba 0 and BaH 2 are both essential is discussed. DFT calculations on benzene hydrogenation with a simple model system (Ba/BaH 2 ) confirm that the presence of metallic Ba has an accelerating effect., (© 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The first intermolecular early main group metal-alkene complexes were isolated. This was enabled by using highly Lewis acidic Mg centers in the Lewis base-free cations ( Me BDI)Mg + and ( tBu BDI)Mg + with B(C 6 F 5 ) 4 - counterions ( Me BDI=CH[C(CH 3 )N(DIPP)] 2 , tBu BDI=CH[C(tBu)N(DIPP)] 2 , DIPP=2,6-diisopropylphenyl). Coordination complexes with various mono- and bis-alkene ligands, typically used in transition metal chemistry, were structurally characterized for 1,3-divinyltetramethyldisiloxane, 1,5-cyclooctadiene, cyclooctene, 1,3,5-cycloheptatriene, 2,3-dimethylbuta-1,3-diene, and 2-ethyl-1-butene. In all cases, asymmetric Mg-alkene bonding with a short and a long Mg-C bond is observed. This asymmetry is most extreme for Mg-(H 2 C=CEt 2 ) bonding. In bromobenzene solution, the Mg-alkene complexes are either dissociated or in a dissociation equilibrium. A DFT study and AIM analysis showed that the C=C bonds hardly change on coordination and there is very little alkene→Mg electron transfer. The Mg-alkene bonds are mainly electrostatic and should be described as Mg 2+ ion-induced dipole interactions., (© 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Commercial LiAlH 4 can be used in catalytic quantities in the hydrogenation of imines to amines with H 2 . Combined experimental and theoretical investigations give deeper insight in the mechanism and identifies the most likely catalytic cycle. Activity is lost when Li in LiAlH 4 is exchanged for Na or K. Exchanging Al for B or Ga also led to dramatically reduced activities. This indicates a heterobimetallic mechanism in which cooperation between Li and Al is crucial. Potential intermediates on the catalytic pathway have been isolated from reactions of MAlH 4 (M=Li, Na, K) and different imines. Depending on the imine, double, triple or quadruple imine insertion has been observed. Prolonged reaction of LiAlH 4 with PhC(H)=NtBu led to a side-reaction and gave the double insertion product LiAlH 2 [N] 2 ([N]=N(tBu)CH 2 Ph) which at higher temperature reacts further by ortho-metallation of the Ph ring. A DFT study led to a number of conclusions. The most likely catalyst for hydrogenation of PhC(H)=NtBu with LiAlH 4 is LiAlH 2 [N] 2 . Insertion of a third imine via a heterobimetallic transition state has a barrier of +23.2 kcal mol -1 (ΔH). The rate-determining step is hydrogenolysis of LiAlH[N] 3 with H 2 with a barrier of +29.2 kcal mol -1 . In agreement with experiment, replacing Li for Na (or K) and Al for B (or Ga) led to higher calculated barriers. Also, the AlH 4 - anion showed very high barriers. Calculations support the experimentally observed effects of the imine substituents at C and N: the lowest barriers are calculated for imines with aryl-substituents at C and alkyl-substituents at N., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

The reagent RK [R=CH(SiMe 3 ) 2 or N(SiMe 3 ) 2 ] was expected to react with the low-valent ( DIPP BDI)Al ( DIPP BDI=HC[C(Me)N(DIPP)] 2 , DIPP=2,6-iPr-phenyl) to give [( DIPP BDI)AlR] - K + . However, deprotonation of the Me group in the ligand backbone was observed and [H 2 C=C(N-DIPP)-C(H)=C(Me)-N-DIPP]Al - K + (1) crystallized as a bright-yellow product (73 %). Like most anionic Al I complexes, 1 forms a dimer in which formally negatively charged Al centers are bridged by K + ions, showing strong K + ⋅⋅⋅DIPP interactions. The rather short Al-K bonds [3.499(1)-3.588(1) Å] indicate tight bonding of the dimer. According to DOSY NMR analysis, 1 is dimeric in C 6 H 6 and monomeric in THF, but slowly reacts with both solvents. In reaction with C 6 H 6 , two C-H bond activations are observed and a product with a para-phenylene moiety was exclusively isolated. DFT calculations confirm that the Al center in 1 is more reactive than that in ( DIPP BDI)Al. Calculations show that both Al I and K + work in concert and determines the reactivity of 1., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Double deprotonation of the diamine 1,1'-(tBuCH 2 NH)-ferrocene (1-H 2 ) by alkaline-earth (Ae) or Eu II metal reagents gave the complexes 1-Ae (Ae=Mg, Ca, Sr, Ba) and 1-Eu. 1-Mg crystallized as a monomer while the heavier complexes crystallized as dimers. The Fe⋅⋅⋅Mg distance in 1-Mg is too long for a bonding interaction, but short Fe⋅⋅⋅Ae distances in 1-Ca, 1-Sr, and 1-Ba clearly support intramolecular Fe⋅⋅⋅Ae bonding. Further evidence for interactions is provided by a tilting of the Cp rings and the related 1 H NMR chemical-shift difference between the Cp α and β protons. While electrochemical studies are complicated by complex decomposition, UV/Vis spectral features of the complexes support Fe→Ae dative bonding. A comprehensive bonding analysis of all 1-Ae complexes shows that the heavier species 1-Ca, 1-Sr, and 1-Ba possess genuine Fe→Ae bonds which involve vacant d-orbitals of the alkaline-earth atoms and partially filled d-orbitals on Fe. In 1-Mg, a weak Fe→Mg donation into vacant p-orbitals of the Mg atom is observed., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Two series of bulky alkaline earth (Ae) metal amide complexes have been prepared: Ae[N(TRIP) 2 ] 2 (1-Ae) and Ae[N(TRIP)(DIPP)] 2 (2-Ae) (Ae=Mg, Ca, Sr, Ba; TRIP=SiiPr 3 , DIPP=2,6-diisopropylphenyl). While monomeric 1-Ca was already known, the new complexes have been structurally characterized. Monomers 1-Ae are highly linear while the monomers 2-Ae are slightly bent. The bulkier amide complexes 1-Ae are by far the most active catalysts in alkene hydrogenation with activities increasing from Mg to Ba. Catalyst 1-Ba can reduce internal alkenes like cyclohexene or 3-hexene and highly challenging substrates like 1-Me-cyclohexene or tetraphenylethylene. It is also active in arene hydrogenation reducing anthracene and naphthalene (even when substituted with an alkyl) as well as biphenyl. Benzene could be reduced to cyclohexane but full conversion was not reached. The first step in catalytic hydrogenation is formation of an (amide)AeH species, which can form larger aggregates. Increasing the bulk of the amide ligand decreases aggregate size but it is unclear what the true catalyst(s) is (are). DFT calculations suggest that amide bulk also has a noticeable influence on the thermodynamics for formation of the (amide)AeH species. Complex 1-Ba is currently the most powerful Ae metal hydrogenation catalyst. Due to tremendously increased activities in comparison to those of previously reported catalysts, the substrate scope in hydrogenation catalysis could be extended to challenging multi-substituted unactivated alkenes and even to arenes among which benzene., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The efficient catalytic reduction of imines with phenylsilane is achieved by using the potassium, calcium and strontium based catalysts [(DMAT)K (THF)] ∞ , (DMAT) 2 Ca⋅(THF) 2 and (DMAT) 2 Sr⋅(THF) 2 (DMAT=2-dimethylamino-α-trimethylsilylbenzyl). Eight different aldimines and the ketimine Ph 2 C=NPh could be successfully reduced by PhSiH 3 at temperatures between 25-60 °C with catalyst loadings down to 2.5 mol %. Also, simple amides like KN(SiMe 3 ) 2 or Ae[N(SiMe 3 ) 2 ] 2 (Ae=Ca, Sr, Ba) catalyze this reaction. Activities increase with metal size. For most substrates the activity increases along the row K

Preference for the binding mode of the CN - ligand to Mg (Mg-CN vs. Mg-NC) is investigated. A monomeric Mg complex with a terminal CN ligand was prepared using the dipyrromethene ligand Mes DPM which successfully blocks dimerization. While reaction of ( Mes DPM)MgN(SiMe 3 ) 2 with Me 3 SiCN gave the coordination complex ( Mes DPM)MgN(SiMe 3 ) 2 ⋅NCSiMe 3 , reaction with ( Mes DPM)Mg(nBu) led to ( Mes DPM)MgNC⋅(THF) 2 . A Mg-NC/Mg-CN ratio of ≈95:5 was established by crystal-structure determination and DFT calculations. IR studies show absorbances for CN stretching at 2085 cm -1 (Mg-NC) and 2162 cm -1 (Mg-CN) as confirmed by 13 C labeling. In solution and in the solid state, the CN ligand rotates within the pocket. The calculated isomerization barrier is only 12.0 kcal mol -1 and the 13 C NMR signal for CN decoalesces at -85 °C (Mg-NC: 175.9 ppm, Mg-CN: 144.3 ppm). Experiment and theory both indicate that Mg complexes with the CN - ligand should not be named cyanides but are more properly defined as isocyanides., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The low-valent ß-diketiminate complex ( DIPP BDI)Al is stable in benzene but addition of catalytic quantities of [( DIPP BDI)CaH] 2 at 20 °C led to ( DIPP BDI)Al(Ph)H ( DIPP BDI=CH[C(CH 3 )N-DIPP] 2 , DIPP=2,6-diisopropylphenyl). Similar Ca-catalyzed C-H bond activation is demonstrated for toluene or p-xylene. For toluene a remarkable selectivity for meta-functionalization has been observed. Reaction of ( DIPP BDI)Al(m-tolyl)H with I 2 gave m-tolyl iodide, H 2 and ( DIPP BDI)AlI 2 which was recycled to ( DIPP BDI)Al. Attempts to catalyze this reaction with Mg or Zn hydride catalysts failed. Instead, the highly stable complexes ( DIPP BDI)Al(H)M( DIPP BDI) (M=Mg, Zn) were formed. DFT calculations on the Ca hydride catalyzed arene alumination suggest that a similar but more loosely bound complex is formed: ( DIPP BDI)Al(H)Ca( DIPP BDI). This is in equilibrium with the hydride bridged complex ( DIPP BDI)Al(μ-H)Ca( DIPP BDI) which shows strongly increased electron density at Al. The combination of Ca-arene bonding and a highly nucleophilic Al center are key to facile C-H bond activation., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Key to the isolation of the first alkyl strontium complex was the synthesis of a strontium hydride complex that is stable towards ligand exchange reactions. This goal was achieved by using the super bulky β-diketiminate ligand DIPeP BDI (CH[C(Me)N-DIPeP] 2 , DIPeP=2,6-diisopentylphenyl). Reaction of DIPeP BDI-H with Sr[N(SiMe 3 ) 2 ] 2 gave ( DIPeP BDI)SrN(SiMe 3 ) 2 , which was converted with PhSiH 3 into [( DIPeP BDI)SrH] 2 . Dissolved in C 6 D 6 , the strontium hydride complex is stable up to 70 °C. At 60 °C, H-D isotope exchange gave full conversion into [( DIPeP BDI)SrD] 2 and C 6 D 5 H. Since H-D exchange with D 2 is facile, the strontium hydride complex served as a catalyst for the deuteration of C 6 H 6 by D 2 . Reaction of [( DIPeP BDI)SrH] 2 with ethylene gave [( DIPeP BDI)SrEt] 2 . The high reactivity of this alkyl strontium complex is demonstrated by facile ethylene polymerization and nucleophilic aromatic substitution with C 6 D 6 , giving alkylated aromatic products and [( DIPeP BDI)SrD] 2 ., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The alkene transfer hydrogenation (TH) of a variety of alkenes has been achieved with simple AeN'' 2 catalysts [Ae=Ca, Sr, Ba; N''=N(SiMe 3 ) 2 ] using 1,4-cyclohexadiene (1,4-CHD) as a H source. Reaction of 1,4-CHD with AeN'' 2 gave benzene, N''H, and the metal hydride species N''AeH (or aggregates thereof), which is a catalyst for alkene hydrogenation. BaN'' 2 is by far the most active catalyst. Hydrogenation of activated C=C bonds (e.g. styrene) proceeded at room temperature without polymer formation. Unactivated (isolated) C=C bonds (e.g. 1-hexene) needed a higher temperature (120 °C) but proceeded without double-bond isomerization. The ligands fully control the course of the catalytic reaction, which can be: 1) alkene TH, 2) 1,4-CHD dehydrogenation, or 3) alkene polymerization. DFT calculations support formation of a metal hydride species by deprotonation of 1,4-CHD followed by H transfer. Convenient access to larger quantities of BaN'' 2 , its high activity and selectivity, and the many advantages of TH make this a simple but attractive procedure for alkene hydrogenation., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

[(BDI)Mg + ][B(C 6 F 5 ) 4 - ] (1; BDI=CH[C(CH 3 )NDipp] 2 ; Dipp=2,6-diisopropylphenyl) was prepared by reaction of (BDI)MgnPr with [Ph 3 C + ][B(C 6 F 5 ) 4 - ]. Addition of 3-hexyne gave [(BDI)Mg + ⋅(EtC≡CEt)][B(C 6 F 5 ) 4 - ]. Single-crystal X-ray analysis, NMR investigations, Raman spectra, and DFT calculations indicate a significant Mg-alkyne interaction. Addition of the terminal alkynes PhC≡CH or Me 3 SiC≡CH led to alkyne deprotonation by the BDI ligand to give [(BDI-H)Mg + (C≡CPh)] 2 ⋅2 [B(C 6 F 5 ) 4 - ] (2, 70 %) and [(BDI-H)Mg + (C≡CSiMe 3 )] 2 ⋅2 [B(C 6 F 5 ) 4 - ] (3, 63 %). Addition of internal alkynes PhC≡CPh or PhC≡CMe led to [4+2] cycloadditions with the BDI ligand to give {Mg + C(Ph)=C(Ph)C[C(Me)=NDipp] 2 } 2 ⋅ 2 [B(C 6 F 5 ) 4 - ] (4, 53 %) and {Mg + C(Ph)=C(Me)C[C(Me)=NDipp] 2 } 2 ⋅2 [B(C 6 F 5 ) 4 - ] (5, 73 %), in which the Mg center is N,N,C-chelated. The (BDI)Mg + cation can be viewed as an intramolecular frustrated Lewis pair (FLP) with a Lewis acidic site (Mg) and a Lewis (or Brønsted) basic site (BDI). Reaction of [(BDI)Mg + ][B(C 6 F 5 ) 4 - ] (1) with a range of phosphines varying in bulk and donor strength generated [(BDI)Mg + ⋅PPh 3 ][B(C 6 F 5 ) 4 - ] (6), [(BDI)Mg + ⋅PCy 3 ][B(C 6 F 5 ) 4 - ] (7), and [(BDI)Mg + ⋅ PtBu 3 ][B(C 6 F 5 ) 4 - ] (8). The bulkier phosphine PMes 3 (Mes=mesityl) did not show any interaction. Combinations of [(BDI)Mg + ][B(C 6 F 5 ) 4 - ] and phosphines did not result in addition to the triple bond in 3-hexyne, but during the screening process it was discovered that the cationic magnesium complex catalyzes the hydrophosphination of PhC≡CH with HPPh 2 , for which an FLP-type mechanism is tentatively proposed., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The steric bulk of the well-known DIPP BDI ligand (CH[C(CH 3 )N-DIPP] 2 , DIPP=2,6-diisopropylphenyl) was increased by replacing isopropyl for isopentyl groups. This very bulky DIPeP BDI ligand could not stabilize the radical species ( DIPeP BDI)Mg . : reduction of ( DIPeP BDI)MgI with Na gave ( DIPeP BDI) 2 Mg 2 with a rather long Mg-Mg bond of 3.0513(8) Å. Addition of TMEDA prior to reduction gave complex ( DIPeP BDI) 2 Mg 2 (C 6 H 6 ), which could also be obtained as its THF adduct. It is speculated that combination of a bulky spectator ligand and TMEDA prevents dimerization of the intermediate Mg I radical, which then reacts with the benzene solvent. Complex ( DIPeP BDI) 2 Mg 2 (C 6 H 6 ), which formally contains the anti-aromatic anion C 6 H 6 2- , reacted with tBuOH as a Brønsted base to 1,3- and 1,4-cyclohexadiene and with H 2 as a two electron donor to ( DIPeP BDI) 2 Mg 2 H 2 and C 6 H 6 . It also reductively cleaved the C-F bond in fluorobenzene and gave ( DIPeP BDI)MgPh, ( DIPeP BDI)MgF, and C 6 H 6 ., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Alkaline earth metal amides (AeN'' 2 : Ae=Ca, Sr, Ba, N''=N(SiMe 3 ) 2 ) catalyze alkene hydrogenation (80-120 °C, 1-6 bar H 2 , 1-10 mol % cat.), with the activity increasing with metal size. Various activated C=C bonds (styrene, p-MeO-styrene, α-Me-styrene, Ph 2 C=CH 2 , trans-stilbene, cyclohexadiene, 1-Ph-cyclohexene), semi-activated C=C bonds (Me 3 SiCH=CH 2 , norbornadiene), or non-activated (isolated) C=C bonds (norbornene, 4-vinylcyclohexene, 1-hexene) could be reduced. The results show that neutral Ca or Ba catalysts are active in the challenging hydrogenation of isolated double bonds. For activated alkenes (e.g. styrene), polymerization is fully suppressed due to fast protonation of the highly reactive benzyl intermediate by N''H (formed in the catalyst initiation). Using cyclohexadiene as the H source, the first Ae metal catalyzed H-transfer hydrogenation is reported. DFT calculations on styrene hydrogenation using CaN'' 2 show that styrene oligomerization competes with styrene hydrogenation. Calculations also show that protonation of the benzylcalcium intermediate with N''H is a low-energy escape route, thus avoiding oligomerization., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Attempted synthesis of the donor-acceptor complex (BDI)Ca + ←Al I (BDI) complex by reaction of (BDI)Ca + in the form of its B(C 6 F 5 ) 4 - salt with (BDI)Al I in benzene led to dearomatization of the solvent and formation of (BDI)Ca + (C 6 H 6 )Al III (BDI) (BDI=CH[C(CH 3 )N-Dipp] 2 , Dipp=2,6-diisopropylphenyl). The C 6 H 6 2- anion is strongly puckered and its boat form features four long (ca. 1.50 Å) and two short (ca. 1.34 Å) C-C bond distances. The flagpole positions of the C 6 H 6 2- anion chelate an Al III cation giving a norbornadiene-like fragment with Al in the 7-position. The C=C double bonds of this alumina-norbornadiene strongly coordinate to the Ca 2+ metal ion. The complex is stable in solution up to 80 °C. Several mechanisms for its formation are discussed including a highly likely frustrated Lewis pair type mechanism in which benzene is activated by the Lewis acid (BDI)Ca + followed by nucleophilic attack by the Lewis base (BDI)Al I ., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report on the development of a supramolecular nanocarrier concept that allows for the encapsulation and separation of small apolar molecules from water. The nanocarriers consist of shell-by-shell-coated nanoparticles such as TiO 2 and ferromagnetic Fe 3 O 4 . The first ligand shell is provided by covalently bound hexadecyl phosphonic acid (PAC 16 ) and the second shell by noncovalently assembled amphiphiles rendering the hybrid architecture soluble in water. Agitation of these constructs with water containing the hydrocarbons G1-G4, the fluorescent marker G5, the polychlorinated biphenyl PCB 77, or crude oil leads to a very efficient uptake (up to 411 %) of the apolar contaminant. In case of the hybrids containing a Fe 3 O 4 core, straightforward phase separation by the action of an external magnet is provided. The load can easily be released by a final treatment with an organic solvent., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Imine-to-amine conversion with catalytic instead of stoichiometric quantities of LiAlH 4 is demonstrated (85 °C, catalyst loading≥2.5 mol %, pressure≥1 bar). The effects of temperature, pressure, solvent, and catalyst modifications, as well as the substrate scope are discussed. Experimental investigations and preliminary DFT calculations suggest that the catalytically active species is generated in situ: LiAlH 4 +Ph(H)C=NtBu→LiAlH 2 [N(tBu)CH 2 Ph] 2 . A cooperative mechanism in which Li and Al both play a prominent role is proposed., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Reaction of Ba[N(SiMe 3 ) 2 ] 2 with PhSiH 3 in toluene gave simple access to the unique Ba hydride cluster Ba 7 H 7 [N(SiMe 3 ) 2 ] 7 that can be described as a square pyramid spanned by five Ba 2+ ions with two flanking BaH[N(SiMe 3 ) 2 ] units. This heptanuclear cluster is well soluble in aromatic solvents, and the hydride 1 H NMR signals and coupling pattern suggests that the structure is stable in solution. At 95 °C, no coalescence of hydride signals is observed but the cluster slowly decomposes to undefined barium hydride species. The complex Ba 7 H 7 [N(SiMe 3 ) 2 ] 7 is a very strong reducing agent that already at room temperature reacts with Me 3 SiCH=CH 2 , norbornadiene, and ethylene. The highly reactive alkyl barium intermediates cannot be observed and deprotonate the (Me 3 Si) 2 N - ion, as confirmed by the crystal structure of Ba 14 H 12 [N(SiMe 3 ) 2 ] 12 [(Me 3 Si)(Me 2 SiCH 2 )N] 4 ., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The first strontium hydride complex has been obtained by simply treating Sr[N(SiMe 3 ) 2 ] 2 with PhSiH 3 in the presence of PMDTA. The Sr complex Sr 6 H 9 [N(SiMe 3 ) 2 ] 3 ⋅(PMDTA) 3 crystallizes as an "inverse cryptand": an interstitial H - is surrounded by a Sr 6 H 8 4+ cage decorated with amide and PMDTA ligands. The analogous Ca complex could also be obtained and both retain their solid-state structures in solution: 1 H NMR spectra in C 6 D 6 show two doublets and one nonet (4:4:1). Up to 90 °C, no coalescence is observed. The Ca cluster was investigated by DFT calculations and shows atypically low charges on Ca (+1.14) and H (-0.59) which signifies an unexpectedly low ionicity. AIM analysis shows hydride⋅⋅⋅hydride bond paths with considerable electron densities in the bond critical point. The clusters thermally decompose into larger, undefined, metal hydride aggregates., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An anionic N-heterocyclic olefin ligand was serendipitously obtained by reaction of an amidinate calcium hydride complex with 1,3-dimethyl-2-methyleneimidazole (NHO). Instead of anticipated addition to the polarized C=CH 2 bond to form an unstabilized alkylcalcium complex, deprotonation of the NHO ligand in the backbone was observed. Preference for deprotonation versus addition is explained by loss of aromaticity in the latter conversion. Theoretical calculations demonstrate the substantially increased ylidic character of this anionic NHO ligand which, like N-heterocyclic dicarbenes, shows strong bifunctional coordination., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

While magnesium hydride complexes are generally stabilized by hard, bulky N-donor ligands, softer ligands with a broad variety of coordination modes are shown to efficiently adapt themselves to the large variety of Mg 2+ centers in a growing magnesium hydride cluster. A P,N-chelating ligand is introduced that displays coordination modes between that of enamide, aza-allyl, and phosphinomethanide. Slight changes in the ligand bite angle have dramatic consequences for the structure type. The hitherto largest neutral magnesium hydride clusters are isolated either in a nonanuclear sheet-structure (brucite-type) or a dodecanuclear ring structure., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Reaction of (TBBP)AlMe⋅THF with [Cp* 2 Zr(Me)OH] gave [(TBBP)Al(THF)-O-Zr(Me)Cp* 2 ] (TBBP=3,3',5,5'-tetra-tBu-2,2'-biphenolato). Reaction of [DIPPnacnacAl(Me)-O-Zr(Me)Cp 2 ] with [PhMe 2 NH] + [B(C 6 F 5 ) 4 ] - gave a cationic Al/Zr complex that could be structurally characterized as its THF adduct [(DIPPnacnac)Al(Me)-O-Zr(THF)Cp 2 ] + [B(C 6 F 5 ) 4 ] - (DIPPnacnac=HC[(Me)C=N(2,6-iPr 2 -C 6 H 3 )] 2 ). The first complex polymerizes ethene in the presence of an alkylaluminum scavenger but in the absence of methylalumoxane (MAO). The adduct cation is inactive under these conditions. Theoretical calculations show very high energy barriers (ΔG=40-47 kcal mol -1 ) for ethene insertion with a bridged AlOZr catalyst. This is due to an unfavorable six-membered-ring transition state, in which the methyl group bridges the metal and ethene with an obtuse metal-Me-C angle that prevents synchronized bond-breaking and making. A more-likely pathway is dissociation of the Al-O-Zr complex into an aluminate and the active polymerization catalyst [Cp* 2 ZrMe] + ., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Simple strategies to obtain magnesium complexes with the soft chelating diylidic ligand [Ph 2 PCHPPh 2 (fluorenylidene)] - (dppmflu - ) were developed to evaluate the influence of the hard acid (cation) and soft base (anion) mismatch on the stability and reactivity of the formed derivatives. Deprotonation of the precursor Ph 2 PCH 2 PPh 2 (flu) (dppmfluH) by an alkylmagnesium derivative or magnesium amide provided access to [{Mg(dppmflu)(μ-nBu)} 2 ], [Mg(dppmflu){N(SiMe 3 ) 2 }], and [{Mg(dppmflu)(μ-Me)} 2 ], which were used as starting materials for further investigations. The reaction of [{Mg(dppmflu)(μ-nBu)} 2 ] with PhSiH 3 in the presence of THF allowed isolation of the magnesium hydride complex [{Mg(dppmflu)(μ-H)(thf)} 2 ] without a stabilizing nitrogen donor ligand. Prolonged heating enforced ligand redistribution and [{Mg(dppmflu)(μ-H)(thf)} 2 ] was converted to [Mg(dppmflu) 2 ] and MgH 2 . The homoleptic derivative [Mg(dppmflu) 2 ], in which the magnesium center is in a very soft ligand environment, can open a THF molecule by frustrated Lewis pair reactivity to give [{Mg(dppmflu)(μ-OC 4 H 8 dppmflu)} 2 ]., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Reaction of the calcium hydride complex (DIPPnacnac-CaH⋅THF)2 with pyridine is much faster and selective than that of the corresponding magnesium hydride complex (DIPPnacnac = [(2,6-iPr2 C6 H3 )NC(Me)]2 CH). With a range of pyridine, picoline and quinoline substrates, exclusive transfer of the hydride ligand to the 2-position is observed and also at higher temperatures no 1,2→1,4 isomerization is found. The heteroleptic product DIPPnacnac-Ca(1,2-dihydropyridide)⋅(pyridine) shows fast ligand exchange into homoleptic calcium complexes and therefore could not be isolated. Calcium hydride reduction of isoquinoline gave well-defined homoleptic products which could be characterized by X-ray diffraction: Ca(1,2-dihydroisoquinolide)2 ⋅(isoquinoline)4 and Ca3 (1,2-dihydroisoquinolide)6 ⋅(isoquinoline)6 . The striking selectivity difference in the dearomatization of pyridines by Mg or Ca complexes could be explained by DFT theory and was utilized in catalysis. Whereas hydroboration of pyridine with pinacol borane with a calcium hydride catalyst gave only minor conversion, the hydrosilylation of pyridine and quinolines with PhSiH3 yields exclusively 1,2-dihydropyridine and 1,2-dihydroquinoline silanes with 80-90 % conversion. Similar results can be achieved with the catalyst Ca[N(SiMe3 )2 ]2 ⋅(THF)2 . These calcium complexes represent the first catalysts for the 1,2-selective hydrosilylation of pyridines., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Organocalcium compounds have been reported as efficient catalysts for various alkene transformations. In contrast to transition metal catalysis, the alkenes are not activated by metal-alkene orbital interactions. Instead it is proposed that alkene activation proceeds through an electrostatic interaction with a Lewis acidic Ca(2+) . The role of the metal was evaluated by a study using the metal-free catalysts: [Ph2 N(-) ][Me4 N(+) ] and [Ph3 C(-) ][Me4 N(+) ]. These "naked" amides and carbanions can act as catalysts in the conversion of activated double bonds (CO and CN) in the hydroamination of ArNCO and RNCNR (R=alkyl) by Ph2 NH. For the intramolecular hydroamination of unactivated CC bonds in H2 CCHCH2 CPh2 CH2 NH2 the presence of a metal cation is crucial. A new type of hybrid catalyst consisting of a strong organic Schwesinger base and a simple metal salt can act as catalyst for the intramolecular alkene hydroamination. The influence of the cation in catalysis is further evaluated by a DFT study., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In analogy to the previously reported tetranuclear magnesium hydride cluster with a bridged dianionic bis-β-diketiminate ligand, a related zinc hydride cluster has been prepared. The crystal structures of these magnesium and zinc hydride complexes are similar: the metal atoms are situated at the corners of a tetrahedron in which the vertices are bridged either by dianionic bis-β-diketiminate ligands or hydride ions. Both structures are retained in solution and show examples of H(-)⋅⋅⋅H(-) NMR coupling (Mg: 8.5 Hz; Zn: 16.0 Hz). The zinc hydride cluster [NN-(ZnH)2]2 thermally decomposes at 90 °C and releases 1.8 equivalents of H2 . In contrast to magnesium hydride clusters, there is no apparent relationship between cluster size and thermal decomposition temperature for the zinc hydrides. DFT calculations reproduced the structure of the zinc hydride cluster reasonably well and charge density analysis showed no bond paths between the hydride ions. This contrasts with calculations on the analogous magnesium hydride cluster in which a counter-intuitive H(-)⋅⋅⋅H(-) bond path was observed. Forcing a reduced H(-)⋅⋅⋅H(-) distance in the zinc hydride cluster, however, gave rise to a H(-)⋅⋅⋅H(-) bond path. Such weak interactions could play a role in H2 desorption. The presumed molecular product after H2 release, a Zn(I) cluster, could not be characterized experimentally but DFT calculations predicted a cluster with two localized Zn-Zn bonds., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The superbulky deca-aryleuropocene [Eu(Cp(BIG))2], Cp(BIG) = (4-nBu-C6H4)5-cyclopentadienyl, was prepared by reaction of [Eu(dmat)2(thf)2], DMAT = 2-Me2N-α-Me3Si-benzyl, with two equivalents of Cp(BIG)H. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45% quantum yield). The crystal structure is isomorphic to those of [M(Cp(BIG))2] (M = Sm, Yb, Ca, Ba) and shows the typical distortions that arise from Cp(BIG)⋅⋅⋅Cp(BIG) attraction as well as excessively large displacement parameter for the heavy Eu atom (U(eq) = 0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp(BIG))2] (M = Sm, Eu, Yb), several physical analyses have been applied. Temperature-dependent magnetic susceptibility data of [Yb(Cp(BIG))2] show diamagnetism, indicating stable divalent ytterbium. Temperature-dependent (151)Eu Mössbauer effect spectroscopic examination of [Eu(Cp(BIG))2] was examined over the temperature range 93-215 K and the hyperfine and dynamical properties of the Eu(II) species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single-crystal X-ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low-frequency torsional and librational modes in [Eu(Cp(BIG))2]. X-ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp(BIG))2] (Ln = Sm, Eu, Yb) compounds are divalent. The XANES white-line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln2O3 standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(Cp(BIG))2] complexes had less trivalent impurity than a [EuI2(thf)x] standard. The complex [Eu(Cp(BIG))2] shows already at room temperature strong orange photoluminescence (quantum yield: 45 %): excitation at 412 nm (24,270 cm(-1)) gives a symmetrical single band in the emission spectrum at 606 nm (νmax =16495 cm(-1), FWHM: 2090 cm(-1), Stokes-shift: 2140 cm(-1)), which is assigned to a 4f(6)5d(1) → 4f(7) transition of Eu(II). These remarkable values compare well to those for Eu(II)-doped ionic host lattices and are likely caused by the rigidity of the [Eu(Cp(BIG))2] complex. Sharp emission signals, typical for Eu(III), are not visible., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new tetranuclear magnesium hydride cluster, [{NN-(MgH)2}2], which was based on a N-N-coupled bis-β-diketiminate ligand (NN(2-)), was obtained from the reaction of [{NN-(MgnBu)2}2] with PhSiH3. Its crystal structure reveals an almost-tetrahedral arrangement of Mg atoms and two different sets of hydride ions, which give rise to a coupling in the NMR spectrum (J = 8.5 Hz). To shed light on the relationship between the cluster size and H2 release, the thermal decomposition of [{NN-(MgH)2}2] and two closely related systems that were based on similar ligands, that is, an octanuclear magnesium hydride cluster and a dimeric magnesium hydride species, have been investigated in detail. A lowering of the H2-desorption temperature with decreasing cluster size is observed, in line with previously reported theoretical predictions on (MgH2)n model systems. Deuterium-labeling studies further demonstrate that the released H2 solely originates from the oxidative coupling of two hydride ligands and not from other hydrogen sources, such as the β-diketiminate ligands. Analysis of the DFT-computed electron density in [{NN-(MgH)2}2] reveals a counterintuitive interaction between two formally closed-shell H(-) ligands that are separated by 3.106 Å. This weak interaction could play an important role in H2 desorption. Although the molecular product after H2 release could not be characterized experimentally, DFT calculations on the proposed decomposition product, that is, the low-valence tetranuclear Mg(I) cluster [(NN-Mg2)2], predict a structure with two almost-parallel, localized Mg-Mg bonds. As in a previously reported β-diketiminate Mg(I) dimer, the Mg-Mg bond is not characterized by a bond critical point, but instead displays a local maximum of electron density midway between the atoms, that is, a non-nuclear attractor (NNA). Interestingly, both of the NNAs in [(NN-Mg2)2] are connected through a bond path that suggests that there is bonding between all four Mg(I) atoms., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

After the lithiation of PYR-H(2) (PYR(2-) =[{NC(Me)C(H)C(Me)NC(6)H(3)(iPr)(2)}(2)(C(5)H(3)N)](2-)), which is the precursor of an expanded β-diketiminato ligand system with two binding pockets, its reaction with [NiBr(2) (dme)] led to a dinuclear nickel(II)-bromide complex, [(PYR)Ni(μ-Br)NiBr] (1). The bridging bromide ligand could be selectively exchanged for a thiolate ligand to yield [(PYR)Ni(μ-SEt)NiBr] (3). In an attempt to introduce hydride ligands, both compounds were treated with KHBEt(3). This treatment afforded [(PYR)Ni(μ-H)Ni] (2), which is a mixed valent Ni(I)-μ-H-Ni(II) complex, and [(PYR-H)Ni(μ-SEt)Ni] (4), in which two tricoordinated Ni(I) moieties are strongly antiferromagnetically coupled. Compound 4 is the product of an initial salt metathesis, followed by an intramolecular redox process that separates the original hydride ligand into two electrons, which reduce the metal centres, and a proton, which is trapped by one of the binding pockets, thereby converting it into an olefin ligand on one of the Ni(I) centres. The addition of a mild acid to complex 4 leads to the elimination of H(2) and the formation of a Ni(II)Ni(II) compound, [(PYR)Ni(μ-SEt)NiOTf] (5), so that the original Ni(II) (μ-SEt)Ni(II) X core of compound 3 is restored. All of these compounds were fully characterized, including by X-ray diffraction, and their molecular structures, as well as their formation processes, are discussed., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cardanol, a constituent of cashew nutshell liquid (CNSL), was subjected to transfer hydrogenation catalyzed by RuCl(3) using isopropanol as a reductant. The side chain of cardanol, which is a mixture of a triene, a diene, and a monoene, was selectively reduced to the monoene. Surprisingly, it is the C8-C9 double bond that is retained with high selectivity. A similar transfer hydrogenation of linoleic acid derivatives succeeded only if the substrate contained an aromatic ring, such as a benzyl ester. TEM and a negative mercury test showed that the catalyst was homogeneous. By using ESI-MS, ruthenium complexes were identified that contained one, two, or even three molecules of substrate, most likely as allyl complexes. The interaction between ruthenium and the aromatic ring determines selectivity in the hydrogenation reaction., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Hydrocarbon-soluble model systems for the calcium-amidoborane-ammine complex Ca(NH(2)BH(3))(2)⋅(NH(3))(2) were prepared and structurally characterized. The following complexes were obtained by the reaction of RNH(2)BH(3) (R = H, Me, iPr, DIPP; DIPP = 2,6-diisopropylphenyl) with Ca(DIPP-nacnac)(NH(2))⋅(NH(3))(2) (DIPP-nacnac = DIPP-NC(Me)CHC(Me)N-DIPP): Ca(DIPP-nacnac)(NH(2)BH(3))⋅(NH(3))(2), Ca(DIPP-nacnac)(NH(2)BH(3))⋅(NH(3))(3), Ca(DIPP-nacnac)[NH(Me)BH(3)]⋅(NH(3))(2), Ca(DIPP-nacnac)[NH(iPr)BH(3)]⋅(NH(3))(2), and Ca(DIPP-nacnac)[NH(DIPP)BH(3)]⋅NH(3). The crystal structure of Ca(DIPP-nacnac)(NH(2)BH(3))⋅(NH(3)(3) showed a NH(2)BH(3)(-) unit that was fully embedded in a network of BH⋅⋅⋅HN interactions (range: 1.97(4)-2.39(4) Å) that were mainly found between NH(3) ligands and BH(3) groups. In addition, there were N-H⋅⋅⋅C interactions between NH(3) ligands and the central carbon atom in the ligand. Solutions of these calcium-amidoborane-ammine complexes in benzene were heated stepwise to 60 °C and thermally decomposed. The following main conclusions can be drawn: 1) Competing protonation of the DIPP-nacnac anion by NH(3) was observed; 2) The NH(3) ligands were bound loosely to the Ca(2+) ions and were partially eliminated upon heating. Crystal structures of [Ca(DIPP-nacnac)(NH(2)BH(3))⋅(NH(3))](∞), Ca(DIPP-nacnac)(NH(2)BH(3))⋅(NH(3))⋅(THF), and [Ca(DIPP-nacnac){NH(iPr)BH(3)}](2) were obtained. 3) Independent of the nature of the substituent R in NH(R)BH(3), the formation of H(2) was observed at around 50 °C. 4) In all cases, the complex [Ca(DIPP-nacnac)(NH(2))](2) was formed as a major product of thermal decomposition, and its dimeric nature was confirmed by single-crystal analysis. We proposed that thermal decomposition of calcium-amidoborane-ammine complexes goes through an intermediate calcium-hydride-ammine complex which eliminates hydrogen and [Ca(DIPP-nacnac)(NH(2))](2). It is likely that the formation of metal amides is also an important reaction pathway for the decomposition of metal-amidoborane-ammine complexes in the solid state., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Complexes of the type [(DIPPnacnac)MgNH(R)BH(3)] have been prepared (DIPPnacnac=CH{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2)). The following substituents R have been used: H, Me, iPr, DIPP (DIPP=2,6-diisopropylphenyl). Complexes [(DIPPnac- nac)MgNH(2)BH(3)].THF, [{(DIPPnac- nac)MgNH(iPr)BH(3)}(2)] and [(DIPPnacnac)MgNH(DIPP)BH(3)] were structurally characterised. The Mg amidoborane complexes decompose at a significantly higher temperature (90-110 degrees C) than the corresponding Ca amidoborane complexes (20-110 degrees C). The complexes with the smaller R substituents (H, Me) gave a mixture of decomposition products of which one could be structurally characterised as [{(DIPPnacnac)Mg}(2)(H(3)B-NMe-BH-NMe)].THF. [{(DIPP- nacnac)MgNH(iPr)BH(3)}(2)] cleanly decomposed to [(DIPPnacnac)MgH], which was characterised as a dimeric THF adduct. The amidoborane complex with the larger DIPP-substituent decomposed into a borylamide complex [(DIPPnacnac)MgN(DIPP)BH(2)], which was structurally characterised as its THF adduct. Bimetallic Mg amidoborane complexes decompose at lower temperatures (60-90 degrees C) and show a different decomposition pathway. The dinuclear Mg amidoborane complexes presented here are based on DIPPnacnac units that are either directly coupled through N-N bonding (abbreviated NN) or through a 2,6-pyridylene bridge (abbreviated PYR). Crystal structures of [PYR-{Mg(nBu)}(2)], [PYR-{MgNH(iPr)BH(3)}(2)], [NN-{MgNH(iPr)BH(3)}(2)]THF and the decomposition products [PYR-Mg(2)(iPrN-BH-iPrN-BH(3))] and [NN-Mg(2)(iPrN-BH-iPrN-BH(3))].THF are presented. The following conclusions can be drawn from these studies: i) The first step in the decomposition of a metal amidoborane complex is beta-hydride elimination, which results in formation of a metal hydride complex and R(H)N=BH(2), ii) depending on the nature of the metal, the metal hydride is either stable and can be isolated or it reacts further, iii) amidoborane anions with small R substituents decompose into the dianionic species (RN-BH-RN-BH(3))(2-), whereas large substituents result in formation of the borylamide RN==BH(2)(-) and iv) enforced proximity of two Mg amidoborane units results in decomposition at a significantly lower temperature and cleanly follows the BNBN pathway.

Calcium reagents Ca(alpha-Me(3)Si-2-Me(2)N-benzyl)(2) x 2 thf (1) and Ca[N(SiMe(3))(2)](2) x 2 thf (2) reacted with silica partially dehydroxylated at 700 degrees C to afford materials that bear ([triple bond]SiO)Ca(alpha-Me(3)Si-2-Me(2)N-benzyl) x 1.6 thf (SiO(2)-1) and ([triple bond]SiO)Ca [N(SiMe(3))(2)] x 1.3 thf (SiO(2)-2) fragments, respectively. Due to the bulk of the supported complexes, the silanol groups are only partially metalated: 50% in SiO(2)-1 and 70% in SiO(2)-2. In the case of SiO(2)-2, a parallel SiMe(3)-capping side reaction affords in fine a silanol-free surface. The materials were characterized by IR spectroscopy, 1D and 2D solid-state high-field NMR spectroscopy, and elemental analysis. Reaction of 2 with one equivalent of the bulky silanol (tBuO)(3)SiOH, a silica-surface mimic, afforded the homoleptic bis-silyloxide calcium derivative through ligand exchange (Schlenk equilibrium), and a derivative was isolated and structurally characterized. Preliminary studies have shown that both grafted benzyl and amide derivatives are active in olefin hydrosilylation, intramolecular hydroamination, and styrene polymerization, with evidence showing that catalysis occurs through supported species. In styrene polymerization, a marked influence of the surface acting as a ligand on the stereoselectivity of the reaction was observed, as syndiotactic-rich polystyrene (88% of r diads) was obtained. These results illustrate that grafting of calcium benzyl or amide compounds on a silica surface is a new concept to prevent ligand exchange through the Schlenk equilibrium. Heteroleptic calcium complexes that cannot be synthesized as stable molecular species in solution can be obtained as silica-supported species which have been shown to be catalytically active.

Size does matter: Whereas geminal bimetallic bis(amidophosphorano)methandiide complexes of the heavy alkali metals K and Rb are relatively stable, that of Cs, the largest and most electropositive of the alkali metals, decomposes to form a cyclic product, which cocrystallizes with benzylcesium.

The reactivity of the hydrocarbon-soluble calcium hydride complex [{CaH(dipp-nacnac)(thf)}(2)] (1; dipp-nacnac=CH{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2)) with a large variety of substrates has been investigated. Addition of 1 to C=O and C=N functionalities gave easy access to calcium alkoxide and amide complexes. Similarly, reduction of the C[triple chemical bond]N bond in a cyanide or an isocyanide resulted in the first calcium aldimide complexes [Ca{N=C(H)R}(dipp-nacnac)] and [Ca{C(H)=NR}(dipp-nacnac)], respectively. Complexation of 1 with borane or alane Lewis acids gave the borates and alanates as contact ion pairs. In reaction with epoxides, nucleophilic ring-opening is observed as the major reaction. The high reactivity of hydrocarbon-soluble 1 with most functional groups contrasts strongly with that of insoluble CaH(2), which is essentially inert and is used as a common drying agent. Crystal structures of the following products are presented: [{Ca{OC(H)Ph(2)}(dipp-nacnac)}(2)], [{Ca{N=C(H)Ph}(dipp-nacnac)}(2)], [{Ca{C(H)=NC(Me)(2)CH(2)C(Me)(3)}(dipp-nacnac)}(2)], [{Ca{C(H)=NCy}(dipp-nacnac)}(2)], [Ca(dipp-nacnac)(thf)](+)[H(2)BC(8)H(14)](-) and [{Ca(OCy)(dipp-nacnac)}(2)]. The generally smooth and clean conversions of 1 with a variety of substrates and the stability of most intermediates against ligand exchange make 1 a valuable key precursor in the syntheses of a wide variety of beta-diketiminate calcium complexes.