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Hybrid catalysts consisting of alkaline earth iodides (AeI2) and the Schwesinger base tBuP4 catalyse the intramolecular alkene hydroamination of H2C=CHCH2CR2CH2NH2 [CR2=CPh2, C(CH2)5, CMe2]. Activities decrease along the row: Ca > Sr >> Mg > Ba. Hybrid catalysts consisting of tBuP4 and ZnI2, AlI3, FeCI3 or NaI were found to be fully inactive. Also, the hybrid catalyst tBuP3/CaI2 was not active which means that the base strength of the non‐nucleophilic organic base must be higher than that of tBuP3 (pKa BH+ = 38.6). Combinations of tBuP4 with CaX2 (X = Cl, Br, OiPr, OTf, NTf2) were found to be fully inactive which may in part be explained by poor solubility. The hybrid catalysis method is therefore limited to the combination tBuP4/CaI2 but the iodide ligands may be partially or fully replaced by chiral ligands. Chiral modifications of the hybrid catalysts gave in intramolecular alkene hydroamination ee values up to 33 %. [ABSTRACT FROM AUTHOR]

Double deprotonation of the diamine 1,1′‐(tBuCH2NH)‐ferrocene (1‐H2) by alkaline‐earth (Ae) or EuII 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 1H 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. [ABSTRACT FROM AUTHOR]

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=SiiPr3, 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. [ABSTRACT FROM AUTHOR]

The first "naked" (Lewis base‐free) cationic Ca amidinate complex [tBuAmDIPPCa(C6H6)]+[B(C6F5)4]– was prepared in 62 % yield {tBuAmDIPP = tBuC(N–DIPP)2; DIPP = 2,6‐diisopropylphenyl} by reaction of [tBuAmDIPPCaH]2 with [Ph3C]+[B(C6F5)4]– in chlorobenzene. The ether‐free complex tBuAmDIPPCaN(SiMe3)2 was obtained by removal of diethyl ether from its ether adduct. Crystal structures show that the amidinate ligand in both complexes is N,Aryl‐chelating. In this coordination mode the bulk of the amidinate ligand is comparable to that of a DIPP‐substituted β‐diketiminate ligand. Isomers with N,N‐coordinating amidinate ligands are circa 15 kcal/mol higher in energy and this coordination mode is only present in case additional ether ligands compensate for energy loss or in case of space limitation at the metal, e.g. in homoleptic (tBuAmDIPP)2Ca. A series of four Ca amidinate complexes, tBuAmDIPPCaX, were tested in the catalytic hydroboration of ketones and aldehydes by pinacolborane (HBpin). Catalytic activities increase for X– = I– < B(C6F5)4– < (Me3Si)2N– ≈ H–. For catalysts with unreactive anions, like I– or B(C6F5)4–, catalyst performance increases with the Lewis acidity of the metal and a mechanism is proposed in which HBpin and ketone coordinate to the Ca2+ ion which is followed by direct hydroboration. The more active catalysts with X– = (Me3Si)2N– or H– likely operate through a mechanism which involves intermediate metal hydride (or borate) complexes. [ABSTRACT FROM AUTHOR]

Porphyrin–hexabenzocoronene architectures serve as good model compounds to study light‐harvesting systems. Herein, the synthesis of porphyrin functionalized hexa‐peri‐hexabenzocoronenes (HBCs), in which one or more porphyrins are covalently linked to a central HBC core, is presented. A series of hexaphenylbenzenes (HPBs) was prepared and reacted under oxidative coupling conditions. The transformation to the respective HBC derivatives worked well with mono‐ and tri‐porphyrin‐substituted HPBs. However, if more porphyrins are attached to the HPB core, Scholl oxidations are hampered or completely suppressed. Hence, a change of the synthetic strategy was necessary to first preform the HBC core, followed by the introduction of the porphyrins. All products were fully characterized, including, if possible, single‐crystal XRD. UV/Vis absorption spectra of porphyrin‐HBCs showed, depending on the number of porphyrins as well as with respect to the substitution pattern, variations in their spectral features with strong distortions of the porphyrins' B‐band. [ABSTRACT FROM AUTHOR]

Abstract: The nickel(0) complex [Ni(bpy)(cod)] (bpy: 2,2′-bipyridine, cod: cycloocta-1,5-diene) was used as a mild reducing reagent for the synthesis of the extremely reactive low-valent palladium complexes [Pd2X2(cod)2] (1: X=Cl, 2: X=Br), Pd(cod)2 (3) and Pd(norbornene)3 (4). The X-ray analysis of 1 showed that the two [Pd(cod)(Cl)] moieties are only connected by a short Pd(I)–Pd(I) bond (bond length: 2.5379(4)Å) with the chloride ions as monodentate ligands. The X-ray structure of 3 which is also known to be an extremely reactive compound could be determined by X-ray diffraction. As expected, the Pd(0) centre is surrounded by the two cod ligands to form a PdC4 tetrahedron with typical Pd–C bond lengths. The crystal structure of 3 shows it to be very similar to the closely related complexes M(cod)2 (M: Ni, Pt). The X-ray structure of 4 displays that the Pd(0) centre is in a trigonal planar environment of the three olefin groups. According to 1H NMR measurements the complexes have the same structure in solution as found in the solid state. [Copyright &y& Elsevier]

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.)

The zinc complexes of chloroquine (CQ; [Zn(CQH + )Cl 3 ]) and hydroxychloroquine (HO-CQ; [Zn(HO-CQH + )Cl 3 ]) were synthesized and characterized by X-Ray structure analysis, FT-IR, NMR, UV-Vis spectroscopy, and cryo-spray mass spectrometry in solid state as well as in aqueous and organic solvent solutions, respectively. In acetonitrile, up to two Zn 2+ ions bind to CQ and HO-CQ through the tertiary amine and aromatic nitrogen atoms (K N-amin CQ  = (3.8 ± 0.5) x 10 4  M -1 and K N-arom CQ  = (9.0 ± 0.7) x 10 3  M -1 for CQ, and K N-amin HO-CQ  = (3.3 ± 0.4) x 10 4  M -1 and K N-arom HO-CQ  = (1.6 ± 0.2) x 10 3  M -1 for HO-CQ). In MOPS buffer (pH 7.4) the coordination proceeds through the partially deprotonated aromatic nitrogen, with the corresponding equilibrium constants of K N-arom(aq) CQ  = (3.9 ± 1.9) x 10 3  M -1 and K N-arom(aq) HO-CQ  = (0.7 + 0.4) x 10 3  M -1 for CQ and HO-CQ, respectively. An apparent partition coefficient of 0.22 was found for [Zn(CQH + )Cl 3 ]. Mouse embryonic fibroblast (MEF) cells were treated with pre-synthesized [Zn((HO-)CQH + )Cl 3 ] complexes and corresponding ZnCl 2 /(HO-)CQ mixtures and zinc uptake was determined by application of the fluorescence probe and ICP-OES measurements. Administration of pre-synthesized complexes led to higher total zinc levels than those obtained upon administration of the related zinc/(hydroxy)chloroquine mixtures. The differences in the zinc uptake between these two types of formulations were discussed in terms of different speciation and character of the complexes. The obtained results suggest that intact zinc complexes may exhibit biological effects distinct from that of the related zinc/ligand mixtures., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Sterically hindered amide anions have found widespread application as deprotonation agents or as ligands to stabilize metals in unusual coordination geometries or oxidation states. The use of bulky amides has also been advantageous in catalyst design. Herein we present s-block metal chemistry with one of the bulkiest known amide ligands: ( t Bu 3 Si) 2 N - (abbreviated: t Bu N - ). The parent amine ( t Bu NH), introduced earlier by Wiberg, is extremely resistant to deprotonation (even with n BuLi/KO t Bu superbases) but can be deprotonated slowly with a blue Cs + /e - electride formed by addition of Cs 0 to THF. ( t Bu N)Cs crystallized as a separated ion-pair, even without cocrystallized solvent. As salt-metathesis reactions with ( t Bu N)Cs are sluggish and incomplete, it has only limited use as an amide transfer reagent. However, ball-milling with LiI led to quantitative formation of ( t Bu N)Li and CsI. Structural characterization shows that ( t Bu N)Li is a monomeric contact ion-pair with a relatively short N-Li bond, an unusual T-shaped coordination geometry around N and extremely short Li⋯Me anagostic interactions. Crystal structures are compared with Li and Cs complexes of less bulky amide ligands (iPr 3 Si) 2 N - ( iPr N - ) and (Me 3 Si) 2 N - ( Me N - ). DFT calculations show trends in the geometries and electron distributions of amide ligands of increasing steric bulk ( Me N - < iPr N - < t Bu N - ) and confirm that t Bu N - is a rare example of a halogen-free weakly coordinating anion., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

More than a century old, magnesium Grignard reagents remain essential to the toolbox of organic chemists. Although similar reagents with the neighbouring group 2 metal Ca have been explored, the considerably higher polarity and reactivity of the Ca-C bond result in undesired decomposition pathways. Ca Grignard reagents have found academic interest but have never fully developed into an established synthetic tool. Recent research activities, however, provide facile access to these highly reactive organocalcium species, including in situ preparation and ball milling approaches to tackle the challenge of controlling their extreme sensitivity. Heavier Grignard reagents are not just more reactive but profit from unique chemical transformations. Insight into the transition metal-like properties of Ca, Sr and Ba is only just emerging. Considering the rapidly developing field of alkaline-earth metal-mediated catalysis, heavy Grignard reagents will probably have a bright future., (© 2023. Springer Nature Limited.)

Inversion barriers Δ G ‡ for planar chiral phosphine-alkene and sulfonamide-alkene hybrid ligands based on phenyl-dibenz[ b,f ]azepine have been determined by density-functional theory calculations. Analysis of the structural and electronic characteristics of the minima and transition states explains the magnitudes of Δ G ‡ and the geometrical changes during the inversion process. The steric repulsion caused by bulky substituents attached to the azepine nitrogen atom has a pronounced effect on the Δ G ‡ value, explaining, inter alia, the stereochemical stability of the P- and S-alkene ligands when compared to the fluxional parent compound where X = H.

Cu(I)-Hydrido complexes supported by dibenzo[ b,f ]azepinyl P -alkene hybrid ligands and stabilized by electrostatic interactions in a Cu-H⋯KCl⋯BR 3 arrangement can be trapped with CO 2 at low temperature to afford Cu(I)-formates. The complexes are isolable with and without a pendant BEt 3 group and show strong Cu-O and weak B-O interactions.

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.)

DFT-Calculations predict that a low-valent complex (BDI)Mg-Ca(BDI) with bulky β-diketiminate (BDI) ligands is thermodynamically stable. It was attempted to isolate such a complex by salt-metathesis between [( DIPeP BDI*)Mg - Na + ] 2 and [( DIPeP BDI)CaI] 2 ( DIPeP BDI = HC[C(Me)N-DIPeP] 2 ; DIPeP BDI* = HC[C( t Bu)N-DIPeP] 2 ; DIPeP = 2,6-CH(Et) 2 -phenyl). Whereas in alkane solvents no reaction was observed, salt-metathesis in C 6 H 6 led to immediate C-H activation of benzene to give ( DIPeP BDI*)MgPh and ( DIPeP BDI)CaH, the latter crystallizing as a THF-solvated dimer [( DIPeP BDI)CaH·THF] 2 . Calculations suggest reduction and insertion of benzene in the Mg-Ca bond. The activation enthalpy for the subsequent decomposition of C 6 H 6 2- into Ph - and H - is only 14.4 kcal mol -1 . Repeating this reaction in the presence of naphthalene or anthracene led to heterobimetallic complexes in which naphthalene 2- or anthracene 2- anions are sandwiched between ( DIPeP BDI*)Mg + and ( DIPeP BDI)Ca + cations. These complexes slowly decompose to their homometallic counterparts and further decomposition products. Complexes in which naphthalene 2- or anthracene 2- anions are sandwiched between two ( DIPeP BDI)Ca + cations were isolated. The low-valent complex ( DIPeP BDI*)Mg-Ca( DIPeP BDI) could not be isolated due to its high reactivity. There is, however, strong evidence that this heterobimetallic compound is a fleeting intermediate., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The previously reported potassium aluminyl complex [(BDI-H)Al - K + ] 2 was converted in Li + or Na + salts by a salt metathesis reaction with Li(BPh 4 ) or Na(BPh 4 ), respectively; BDI-H = dianionic [(DIPP)N-C(Me)C(H)-C(CH 2 )-N(DIPP) 2- ] and DIPP = 2,6-diisopropylphenyl. The Rb and Cs aluminyl complexes were obtained by reaction of (BDI)Al with RbC 8 or CsC 8 ; BDI = HC[C(Me)N(DIPP)] 2 . Crystal structures of two monomers, (BDI-H)Al - Li + ·(Et 2 O) 2 and (BDI-H)Al - Na + ·(Et 2 O)(TMEDA), and four dimers [(BDI-H)Al - M + ] 2 (M = Li, Na, Rb, Cs) are discussed. Lewis base-free dimers [(BDI-H)Al - M + ] 2 crystallize either as slipped dimers (Li + , Na + ) in which each Al center features only one Al-M contact or as a symmetric dimer (K + , Rb + , Cs + ) in which the cation bridges both Al centers. The dimer with the largest cation (Cs + ) shows Cs⋯CH 2 C interactions between dimers, resulting in a coordination polymer. AIM and charge analysis reveal highly ionic Al-M bonds with strong polarization of the Al lone-pair towards the smaller cation Li + and Na + . The Al-M bonds become weaker from Li to Cs. Calculated dimerization energies suggest that in apolar solvents only complexes with the heavier metals Rb and Cs may be in a monomer-dimer equilibrium. This is confirmed by DOSY measurements in benzene. Dimeric aluminyl complexes with heavier alkali metals (K-Cs) react with benzene to give a double C-H activation in para -positions.

Oxidative addition of 1.5 equiv of bromine or iodine to a Ir(I) sulfoxide pincer complex affords the corresponding Ir(IV) tris-bromido or tris-iodido complexes, respectively. The unprecedented trap-free reductive elimination of iodine from the Ir(IV)-iodido complex is induced by coordination of ligands or donor solvents. In the case of added I - , the isostructural tris-iodo Ir(III)-ate complex is quickly generated, which then can be readily reoxidized to the Ir(IV)-iodido complex with FcPF 6 or electrochemically. DFT calculations indicate an "inverted ligand field" in the Ir(IV) complexes and favor dinuclear pathways for the reductive elimination of iodine from the formal d 5 metal center.

The chiral building block (R)-(+)-2,2'-diamino-1,1'-binaphthyl, (R)-BINAM, which is often used as backbone in privileged enantioselective catalysts, was converted to a series of N-substituted proligands R1-H2 (R = CH2tBu, C(H)Ph2, PPh2, dibenzosuberane, 8-quinoline). After double deprotonation with strong Mg or Ca bases, a series of alkaline earth (Ae) metal catalysts R1-Ae·(THF)n was obtained. Crystal structures of these C2-symmetric catalysts have been analyzed by quadrant models which show that the ligands with C(H)Ph2, dibenzosuberane and 8-quinoline substituents should give the best steric discrimination for the enantioselective intramolecular alkene hydroamination (IAH) of the aminoalkenes H2C[double bond, length as m-dash]CHCH2CR'2CH2NH2 (CR'2 = CPh2, CCy or CMe2). The dianionic R12- ligand in R1-Ae·(THF)n functions as reagent that deprotonates the aminoalkene substrate, while the monoanionic (R1-H)- ligand formed in this reaction functions as a chiral spectator ligand that controls the enantioselectivity of the ring closure reaction. Depending on the substituent R in the BINAM ligand, full cyclization of aminoalkenes to chiral pyrrolidine products as fast as 5 minutes was observed. Product analysis furnished enantioselectivities up to 57% ee, which marks the highest enantioselectivity reported for Ca catalyzed IAH. Higher selectivities are impeded by double protonation of the R12- ligand leading to complete loss of chiral information in the catalytically active species.

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.)

Complexes of the Lewis base-free cations ( Me BDI)Mg + and ( t Bu BDI)Mg + with Ph-X ligands (X = F, Cl, Br, I) have been studied ( Me BDI = HC[C(Me)N-DIPP] 2 and t Bu BDI = HC[C( t Bu)N-DIPP] 2 ; DIPP = 2,6-diisopropylphenyl). For the smaller β-diketiminate ligand ( Me BDI) only complexes with PhF could be isolated. Heavier Ph-X ligands could not compete with bonding of Mg to the weakly coordinating anion B(C 6 F 5 ) 4 - . For the cations with the bulkier t Bu BDI ligand, the full series of halobenzene complexes was structurally characterized. Crystal structures show that the Mg⋯X-Ph angle strongly decreases with the size of X: F 139.1°, Cl 101.4°, Br 97.7°, I 95.1°. This trend, which is supported by DFT calculations, can be explained with the σ-hole which increases from F to I. Charge calculation and Atoms-In-Molecules analyses show that Mg⋯F-Ph bonding originates from electrostatic attraction between Mg 2+ and the very polar C δ + -F δ - bond. For the heavier halobenzenes, polarization of the halogen atom becomes increasingly important (Cl < Br < I). Complexation with Mg leads in all cases to significant Ph-X bond activation and elongation. This unusual coordination of halogenated species to early main group metals is therefore relevant to C-X bond breaking., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

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.)

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.)

The synthesis of a new iridium(I) complex containing an enamido phosphine anion (dbuP - ) and its unique reactivity with CO 2 is reported. The complex binds two equivalents of CO 2 and initiates a highly selective reaction cascade. The reaction leads to the reversible cleavage of CO 2 and the enamido ligand as well. Computational analysis points to the existence of a relatively stable Ir-CO 2 complex as a reaction intermediate prior to CO 2 cleavage, which was confirmed experimentally. The observed transformation resembles several aspects of enzymatic CO 2 fixation by RuBisCO., (© 2018 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.)

A general procedure was developed for the synthesis of diarylcalcium complexes by addition of KOtBu to arylcalcium iodides in THF. Intermediate arylcalcium tert-butanolate dismutates immediately leading to insoluble tert-butanolate precipitates of calcium. Depending on the steric demand and denticity of additional neutral aliphatic azabases, mononuclear or dinuclear complexes trans-[Ca(α-Naph)2(thf)4] (1), [Ca(β-Naph)2(thf)4] (2), [Ca(Tol)2(tmeda)]2 (3), [Ca(Ph)2 (tmeda)]2 (4), [Ca(Ph)2(pmdta)(thf)] (5), [Ca(hmteta)(Ph)2] (6), and [Ca([18]C-6)(Ph)2] (7) were isolated (Naph=naphthyl; meda=N,N,N',N'-tetramethylethylenediamine; pmdta= N,N,N',N'',N''-pentamethyldiethylenetriamine; hmteta=N,N,N',N'',N''',N'''-hexamethyltriethylenetetramine). The Ca-C bond lengths vary between 250.8 and 263.5 pm, the ipso-carbon atoms show low-field-shifted resonances in the (13) C NMR spectra., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In the title compound, [Ni(2)(C(2)H(4))(2)(C(25)H(22)P(2))(2)]·2C(7)H(8), each Ni atom is coordinated in a trigonal-planar geometry by two P atoms of the bridging 1,2-bis-(diphenyl-phosphino)methane (dppm) ligands and by the centroid of the double bond of an ethene ligand. An eight-membered ring comprising the two Ni atoms, four P atoms and the CH(2) groups of the two dppm ligands is thus formed. The methyl group in one of the solvent toluene mol-ecules is disordered over two positions with equal occupancies.

Organocalcium chemistry is still in its infancy. The direct synthesis of activated calcium and (substituted) iodobenzenes allows for the large-scale and high-yield synthesis of aryl calcium iodides. The influence of the substitution patterns of the phenyl group, halogen atom, and solvent is discussed. Aryl calcium iodides show a Schlenk equilibrium that enables the isolation of diaryl calcium derivatives. Owing to the high reactivity of aryl calcium halides, low temperatures have to be maintained throughout the preparative procedures in order to avoid side reactions. A decrease of reactivity and, hence, an enhanced stability at higher temperatures can be achieved by shielding of the calcium atom by increasing the coordination number of the metal center or by substitution of the iodide anion by bulky groups.

The reaction of a nickelalactone with dppm, resulting in the formation of a stable binuclear Ni(I) complex with an acrylate, a Ph2P- and a dppm bridge, models a key step in the formation of acrylic acid from CO2 and ethylene.