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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.)

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.)

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 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.)

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.)

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.)

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.)

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.)

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.

Tackling tacticity: The first well-defined heteroleptic benzylcalcium complex initiates the living polymerization of styrene. Chain-end control results in a polymer enriched in syndiotactic sequences. Stereo errors arise from fast inversion of the chiral carbanionic chain end. Increasing the styrene concentration accelerates the insertion and leads to a considerable reduction of the stereo errors., (Copyright © 2001 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)

A [Cp 3 Ba] ∞ coordination polymer with a chain structure is present in the compound [Cp 3 Ba] - [Bu 4 P] + . The barium center is tetrahedrally coordinated by four η 5 -Cp rings (a section of the chain is shown on the right). The Bu 4 P cations bridge neighboring [Cp 3 Ba] ∞ chains through short hydrogen bonds, and the cocrystallized THF molecules do not coordinate to the barium centers but are instead involved in short CH⋅⋅⋅O hydrogen bonds with the Bu 4 P cations., (© 1998 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)