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Past one decade has witnessed a tremendous growth in the field of carbene stabilized low‐valent silicon compounds unravelling very exciting properties of these molecules. Herein, we have employed a bicyclic (alkyl)(amino)carbene, (MeBICAAC) to explore the low‐valent chemistry of silicon. The reduction of bicyclic (alkyl)(amino)carbene‐SiCl4 complex, [(MeBICAAC)SiCl4] (1) with KC8 afforded low‐valent Si complexes, including Si(III) radical [(MeBICAAC)SiCl3] (2) and a complex with silicon center in a formal zero‐valent state, [(MeBICAAC)2Si] (3). Similarly, the reduction of in‐situ generated MeBICAAC adduct of Me2SiCl2 with one equivalent of KC8 led to the formation of [(MeBICAAC)SiMe2Cl] (4) complex having an unpaired electron. These complexes have been characterized by IR, UV‐Vis. NMR, HRMS, EPR and their solid‐state structures were also elucidated by single crystal X‐ray crystallography. Further, DFT calculations revealed the lower energy singlet state for complexes 1, 3 and doublet state for complexes 2, 4. [ABSTRACT FROM AUTHOR]

Attempts to create a novel Mg−Be bond by reaction of [(DIPePBDI*)MgNa]2 with Be[N(SiMe3)2]2 failed; DIPePBDI*=HC[(tBu)C=N(DIPeP)]2, DIPeP=2,6‐Et2C‐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 (DIPePBDI*)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 (DIPPBDI)Mg−Mg(DIPPBDI) 55.8 kcal mol−1). Natural‐Population‐Analysis (NPA) shows fragment charges: (DIPePBDI*)Mg +0.27/BeCp* −0.27. The very low NPA charge on Be (+0.62) compared to Mg (+1.21) and the strongly upfield 9Be NMR signal at −23.7 ppm are in line with considerable electron density on Be and the formal oxidation state assignment of MgII−Be0. Despite this Mgδ+−Beδ− polarity, 1 is extremely thermally stable and unreactive towards H2, CO, N2, cyclohexene and carbodiimide. It reacted with benzophenone, azobenzene, phenyl acetylene, CO2 and CS2. Reaction with 1‐adamantyl azide led to reductive coupling and formation of an N6‐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. [ABSTRACT FROM AUTHOR]

Silacycloheptatriene (silepin) species are novel silicon compounds reported in recent years. The interplay between the "closed" silepin and the "open" silylene form enables an enhanced stability of the low valent species while maintaining a high reactivity towards small molecules. In this work, two new silepins of similar structures to literature known compounds bearing modified silyl ligands are reported. A unique intramolecular activation of an aromatic hydrogen is found, and the respective formed hydrosilanes are characterized. We further synthesized iron(0) carbonyl complexes of known and new silepins in order to investigate their electronic properties relative to each other to gain more insight into substitution effect in such compounds. [ABSTRACT FROM AUTHOR]

A low‐valent GaI complex with the superbulky β‐diketiminate ligand DIPePBDI (HC[C(Me)N−DIPeP]2, DIPeP=2,6‐C(H)Et2‐phenyl)) was obtained by reduction of (DIPePBDI)GaI2 (1) with KC8 in toluene. Considering that (BDI)GaI and analogue (BDI)AlI complexes are prone to decomposition and can generally only be obtained in low yields (20–40 %), the quantitative formation of (DIPePBDI)GaI (2) is remarkable and no doubt related to its excellent thermal stability even in refluxing toluene. Although the low‐valent metal center in 2 is sterically protected by the superbulky DIPePBDI ligand, it is readily oxidized by N2O to give intermediate (DIPePBDI)Ga=O which readily decomposed by abstracting a proton from the backbone Me‐substituent. Reaction with trimethylsilyl azide gave an intermediate imido complex (DIPePBDI)Ga=N(SiMe3)2 which reacted with a second equivalent of Me3SiN3 to a mixture of an azide/amido complex (DIPePBDI)GaN3[N(SiMe3)2] (4) and a tetrazagallole complex (DIPePBDI)Ga[N4(SiMe3)2] (5) in a 1 : 2 ratio. Whereas the azide/amido complex 4 could be structurally characterised, the tetraazagallole complex 5 was identified by NMR spectroscopy. DFT calculations on (DIPePBDI)GaI (2) and its reaction products complement this study. [ABSTRACT FROM AUTHOR]

Monoanionic N,N‐chelating triazenide ligands, [R‐NNN‐R]−, are compared to formamidinate or β‐diketiminate ligands considerably less electron‐donating and therefore potentially suitable for stabilizing electron rich metals in low oxidations states. A feature reported for silyl‐substituted triazenide ligands, is their ability to eliminate N2 resulting in (R3Si)2N− anions. Here we describe a series of group 1 and 2 metal complexes with the very bulky bis‐silyl‐triazenide ligand [tBu3Si‐NNN‐SitBu3]−. Heteroleptic complexes could be isolated for Mg: {[(tBu3Si)2N3]MgnBu}2 or {[(tBu3Si)2N3]MgI}2, including its ether adducts. Despite bulky silyl substituents, the ligand did not stabilize heteroleptic [(tBu3Si)2N3]AeN(SiMe3)2 complexes for Ca, Sr and Ba and only homoleptic Ae[(tBu3Si)2N3]2 complexes were isolated. Thermal decomposition of these complexes did result in N2 elimination and formation of the expected amide complexes. Reduction of [(tBu3Si)2N3]MgI ⋅ (Et2O) with KC8 in Et2O led to the formation of a MgI complex with a Mg−Mg bond length of 2.902(1) Å. As only one of the Mg centres shows coordination with a Et2O ligand, this is a rare example of an asymmetric Mg−Mg bond. This MgI complex is rather unstable in benzene solution, likely due to reduction of the ligand system. Triazenide ligands are therefore not suitable for stabilization of group 2 metals in low oxidation states. [ABSTRACT FROM AUTHOR]

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′′)⋅Et2O]8. Dissolution in benzene or toluene led to replacement of the Et2O ligand with a softer arene ligand and isolation of Ba(Anth′′)⋅arene. Diffusion ordered spectroscopy (DOSY NMR) measurements in benzene‐d6 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 Ba2+/Anth′′2− bonding. Preliminary reactivity studies with air, Ph2C=NPh, or H2 show that the complex reacts as a Ba0 synthon by release of neutral Anth′′. This soluble molecular Ba0/BaII redox synthon provides new routes for the syntheses of barium complexes under mild conditions. [ABSTRACT FROM AUTHOR]

• A new. very bulky dipyrromethenide (DPM) ligand with 10-isopropyl-9-anthracenyl substituents is introduced. • First monomeric GaI complexes with bulky DPM ligands are reported. • It is shown that the reaction of (DPM)GaI complexes with Me 3 Si-azide selectively gave only tetrazagallole (DPM)Ga[N 4 (SiMe 3) 2 ] or amide/azide product (DPM)Ga(N 3)N(SiMe 3) 2. • It is shown that this selectivity can be controlled with the substituent on the DPM ligand. Following the recent isolation and structural characterization of the first low-valent GaI complex with a monoanionic dipyrromethenide ligand (DPM), herein (DPM)GaI complexes with bulky aryl-substituents in the 1- and 9-positions are described. This study focusses on three DPM ligands with mesityl substituents (MesDPM), 2,6-diisopropylphenyl substituents (DIPPDPM), or 10-isopropyl-9-anthracenyl substituents (iPr-AnthDPM); the synthesis to the latter unknown ligand is described. The precursors (RDPM)GaI 2 were obtained by reaction of the corresponding alkali metal complexes (RDPM)M (M = Na or K) with GaI 3 and characterized by X-ray diffraction. Crystal structures show the efficient shielding of the GaI 2 unit by two flanking aryl groups. In a subsequent reduction step, (DIPPDPM)GaI and (iPr-AnthDPM)GaI have been isolated. Comparison of the crystal structure of (DIPPDPM)GaI with that of a similar β-diketiminate GaI complex shows that the Ga center in the DPM complex is well shielded by flanking DIPP substituents. Despite this favorable ligand geometry, isolation of the corresponding (DPM)Ga= N (SiMe 3) complexes failed due to further reaction with a second equivalent of Me 3 SiN 3. This resulted in clean formation of the tetrazagallole complex (tBuDPM)Ga[N 4 (SiMe 3) 2 ] and the amide/azide combination (iPr-AnthDPM)Ga(N 3)N(SiMe 3) 2 , both structurally characterized by X-ray diffraction. Selective formation of both complexes shows that the substituents in the DPM ligand effectively control the course of the reaction. DFT calculations show that independent of the substituent (t Bu, DIPP, or i Pr-Anth) the amide/azide combination is always circa 20 kcal/mol more stable than the tetrazagallole product. The latter must therefore be formed by kinetic control. Low-valent GaI complexes with dipyrromethene ligands feature a highly shielded metal center. Depending on the nature of the bulky substituents, the reaction wit Me 3 Si-azide either gives a tetrazagallole product or an amide/azide combination. [Display omitted] [ABSTRACT FROM AUTHOR]

Complex [(DIPePBDI)Ca]2(C6H6), with a C6H62− dianion bridging two Ca2+ ions, reacts with benzene to yield [(DIPePBDI)Ca]2(biphenyl) with a bridging biphenyl2− dianion (DIPePBDI=HC[C(Me)N‐DIPeP]2; DIPeP=2,6‐CH(Et)2‐phenyl). The biphenyl complex was also prepared by reacting [(DIPePBDI)Ca]2(C6H6) with biphenyl or by reduction of [(DIPePBDI)CaI]2 with KC8 in presence of biphenyl. Benzene‐benzene coupling was also observed when the deep purple product of ball‐milling [(DIPPBDI)CaI(THF)]2 with K/KI was extracted with benzene (DIPP=2,6‐CH(Me)2‐phenyl) giving crystalline [(DIPPBDI)Ca(THF)]2(biphenyl) (52 % yield). Reduction of [(DIPePBDI)SrI]2 with KC8 gave highly labile [(DIPePBDI)Sr]2(C6H6) as a black powder (61 % yield) which reacts rapidly and selectively with benzene to [(DIPePBDI)Sr]2(biphenyl). DFT calculations show that the most likely route for biphenyl formation is a pathway in which the C6H62− dianion attacks neutral benzene. This is facilitated by metal‐benzene coordination. [ABSTRACT FROM AUTHOR]

We describe the reactions of amido‐EII hydride complexes, PhiPDippEH (PhiPDipp={[Ph2PCH2SiiPr2](Dipp)N}−; Dipp=2,6‐iPr2C6H3; E=Ge (5), Sn (6)), towards the oxonium complex [(Et2O)2H][BArF4] (ArF=3,5‐CF3‐C6H3). For 5, formation of the dihydro‐tetrylium complex (i. e. [PhiPDippGeH2][BArF4], (7)) is favoured, in contrast to the same reaction for 6 which selectively leads to H2 elimination, furnishing the novel tetryliumylidene [PhiPDippSn][BArF4] (4). The related cationic GeII complex (i. e. [PhiPDippGe][BArF4] (3)) could be accessed via the often utilised chloride abstraction route with Na[BArF4]. The high Lewis acidity of this species has been demonstrated through the reaction of 3 towards the nitrogen bases, NH3 and 4‐dimethylaminopyridine. In the latter case, a classic donor‐acceptor complex is formed. Conversely, for NH3, the [DippN] fragment of the ligand is intriguingly displaced by [HN], presumably through double proton‐transfer in loss of DippNH2. [ABSTRACT FROM AUTHOR]

Mechanochemistry has great potential in the syntheses of low‐valent Mg(I) complexes. Magnesium iodide precursors with three different β‐diketiminate (BDI) ligands of varying bulk have been reduced with K/KI (or Na/NaCl) using the ball‐mill. Depending on the steric bulk of the ligand, the raw products are intensely colored powders, indicating the presence of (BDI)Mg⋅ radicals. Extraction with pentane gave (BDI)Mg−Mg(BDI) in excellent yields. Reaction of the powder with H2 prior to extraction gave [(BDI)MgH]2. Extraction with benzene gave (BDI)Mg(C6H6)Mg(BDI) with a dearomatized puckered benzene dianion. Ball‐milling in the presence of triphenylbenzene gave a dinuclear Mg complex with a Ph3C6H3‐dianion which slowly decomposed to (BDI)Mg−Mg(BDI) and Ph3C6H3. [ABSTRACT FROM AUTHOR]

Several methods for the oxidation of the β‐diketiminate AlI complexes (BDI)Al and (BDI*)Al with O2, Et3P=O or N2O are presented (BDI=HC[C(Me)N(DIPP)]2, DIPP=2,6‐diisopropylphenyl; BDI*=HC[C(tBu)N(DIPP)]2). The selectivity of alumoxane formation depends strongly on the nature of the β‐diketiminate ligand, the experimental procedure and the solvent. The mononuclear alumoxanes (BDI)Al=O and (BDI*)Al=O are highly reactive intermediates that cannot be isolated but either aggregate to give less reactive dimers or decompose by internal C−H activation of a backbone Me group or an iPr group. Ethereal solvents like Et2O react with alumoxanes to give (BDI)Al(OEt)OH and ethylene by β‐H elimination. In case of N2O oxidation, subsequent reaction with a second equivalent of N2O to form the hyponitrite complexes (BDI)Al(N2O2) and (BDI*)Al(N2O2) is observed. Details of the alumoxane formation, reactivity and decomposition have been obtained by DFT calculations. These calculations also underscore their rather bipolar character, represented by the resonance structure (BDI)Al+−O−, and estimate the σ‐ and π‐bond character of the Al=O bond at circa 76 % and 24 %, respectively. [ABSTRACT FROM AUTHOR]

Anionic, metal‐centered nucleophiles are emerging compounds with unique reactivities. Here, we describe the isolation and full characterization of the first tetraamido tin(II) dianion, its behavior as ligand towards transition metals, and its reactivity as a tin‐centered nucleophile. Experimental values such as the Tolman electronic parameter (TEP) and computations attest tin‐located σ‐donor ability exceeding that of carbenes or electron‐rich phosphines. Against transition metals, the stannate(II) can act as η1‐ or η5‐type ligand. With aldehydes, it reacts by hydride substitution to give valuable acyl stannates. The reductive dehalogenation of iodobenzene indicates facile redox pathways mediated by halogen bond interaction. Calix[4]pyrrolato stannate(II) represents the first example of this macrocyclic ligand in low‐valent p‐block element chemistry. [ABSTRACT FROM AUTHOR]

The use of a sodium in sodium chloride dispersion is systematically evaluated for the synthesis of nickel(0) and nickel(I) complexes from readily‐prepared nickel(II) precursors. A variety of complexes with phosphine and bipyridine‐type ligands were accessed, although some reactions were found to produce mixtures of nickel(0) and nickel(I), and yields were highly variable. Several new nickel(I) complexes were obtained, and these were characterized using techniques including NMR spectroscopy, EPR spectroscopy, and single crystal X‐ray diffraction analysis. [ABSTRACT FROM AUTHOR]

Low‐valent uranium‐element multiple bond complexes remain scarce, though there is burgeoning interest regarding to their bonding and reactivity. Herein, isolation of a uranium(III)‐carbon double bond complex [(Cp*)2U(CDP)](BPh4) (1) comprising a tridentate carbodiphosphorane (CDP) was reported for the first time. Oxidation of 1 afforded the corresponding U(IV) complex [(Cp*)2U(CDP)](BPh4)2 (2). The distance between U and C in 2 is 2.481 Å, indicating the existence of a typical U=C double bond, which is further confirmed by quantum chemical calculations. Bonding analysis suggested that the CDP also serves as both σ‐ and π‐donor in complex 1, though a longer U−C bond (2.666(3) Å) is observed. It implies that 1 is the first isolable mononuclear uranium(III) carbene complex. Moreover, these results suggest that CDPs are promising ligands to establish other low‐valent f‐block metal‐carbon multiple bond complexes. [ABSTRACT FROM AUTHOR]

The isolation of simultaneously low‐coordinate and low‐valent compounds is a timeless challenge for preparative chemists. This work showcases the preparation and full characterization of tri‐coordinate rhodium(‐I) and rhodium(0) complexes as well as a rare rhodium(I) complex. Reduction of [{Rh(μ‐Cl)(IPr)(dvtms)}2] (1, IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazolyl‐2‐ylidene; dvtms=divinyltetramethyldisiloxane) with KC8 gave the trigonal complexes K[Rh(IPr)(dvtms)] and [Rh(IPr)(dvtms)], whereas the cation [Rh(IPr)(dvtms)]+ results from their oxidation or by abstraction of chloride from 1 with silver salts. The paramagnetic Rh0 complex is a unique fully metal‐centered radical with the unpaired electron in the dz2 orbital. The Rh(‐I) complex reacts with PPh3 with replacement of the NHC ligand, and behaves as a nucleophile, which upon reaction with [AuCl(PPh3)] generates the trigonal pyramidal complex [(IPr)(dvtms)Rh‐Au(PPh3)] with a metal–metal bond between two d10 metal centers. [ABSTRACT FROM AUTHOR]

New 10π-electron stabilized O,N-heterocyclic germylene was synthesized and structurally characterized for the first time. Its reduction with potassium in THF resulted in a unique low-valent germanium compound comprising the conjugated Ge 4 chain, which was also characterized by the single crystal X-ray analysis. Bonding aspects in the latter compound have been additionally explored by DFT calculations, which revealed the occurrence of three σ bonds of different (covalent and dative) characters between the Ge atoms. [ABSTRACT FROM AUTHOR]

Treatment of bis(mesitylene)niobium(0) with 6–7 equivalents of 2,6‐dimethylphenyl isocyanide (CNXyl) affords two products with the empirical formula Nb(CNXyl)n (n = 7 or 6), which have been shown to be the diamagnetic dimers bis[μ‐N,N′,N′′,N′′′‐tetrakis(2,6‐dimethylphenyl)squaramidinato(2−)]bis[pentakis(2,6‐dimethylphenyl isocyanide)niobium(I)], [Nb2(C9H9N)10(C36H36N4)] or [Nb(CNXyl)5]2[μ‐C4(NXyl)4]·xSolvent, 1, and bis[μ‐N,N′,N′′,N′′′‐tetrakis(2,6‐dimethylphenyl)squaramidinato(2−)]bis[tetrakis(2,6‐dimethylphenyl isocyanide)niobium(I)] tetrahydrofuran trisolvate, [Nb2(C9H9N)8(C36H36N4)]·3C4H8O or [Nb(CNXyl)4]2[μ‐C4(NXyl)4]·3THF (THF = tetrahydrofuran), 2. Each contains NbI bound to either five or four terminal isocyanides, respectively, and to an unprecedented bridging tetraarylsquaramidinate(2−) unit, coordinated as a bidentate ligand to each niobium center, symmetrically due to the crystallographic inversion center that coincides with the centroid of the central C4 unit. Thus, in the presence of CNXyl, the bis(mesitylene)niobium(0) is oxidized to niobium(I), resulting in the facile loss of both mesitylene groups and the reductive coupling of two CNXyl groups per niobium to provide the first examples of tetraarylsquaramidinate(2−) ligands, [cyclo‐C4N4Ar4]2−, coordinated to metals. In contrast, bis(mesitylene)niobium(0) reacts with the more crowded 2,6‐diisopropylphenyl isocyanide (CNDipp) to afford the paramagnetic monomer hexakis(2,6‐diisopropylphenyl isocyanide)niobium(0), [Nb(C13H17N)6] or Nb(CNDipp)6, 3, the first zero‐valent niobium isocyanide analog of the highly unstable Nb(CO)6, which is presently only known to exist in an argon matrix at 4.2 K. [ABSTRACT FROM AUTHOR]

Since the latter quarter of the twentieth century, main group chemistry has undergone significant advances. Power's timely review in 2010 highlighted the inherent differences between the lighter and heavier main group elements, and that the heavier analogues resemble transition metals as shown by their reactivity towards small molecules. In this concept article, we present an overview of the last 10 years since Power's seminal review, and the progress made for catalytic application. This examines the use of low oxidation state and/or low coordinate group 13 and 14 complexes towards small molecule activation (oxidative addition step in a redox based cycle) and how ligand design plays a crucial role in influencing subsequent reactivity. The challenge in these redox based catalytic cycles still centres on the main group complexes' ability to undergo reductive elimination, however considerable progress in this field has been reported via reversible oxidative addition reactions. Within the last 5 years the first examples of well‐defined low valent main group catalysts have begun to emerge, representing a bright future ahead for main group chemistry. Main concept: This concept article presents the last 10 years of molecular main group chemistry since Power's seminal review and the progress made towards catalysis. [ABSTRACT FROM AUTHOR]

Abstract: The experimental synthesis of quintet [V(AIP)]2(μ‐C6H6) and septet [Cr(AIP)]2(μ‐C6H6) analogues provide a new strategy to produce high spin multiplicity by utilizing inverse sandwiches. Aiming to design higher spin multiplicity, [M(AIP)]2(μ‐C4H4) (M = Cr, V) using C4H4 as central ligand are theoretically proposed. For [V(AIP)]2(μ‐C4H4), the most stable isomer group contains the septet and the open‐shell singlet isomers, which have three unpaired electrons on each V atoms. For [Cr(AIP)]2(μ‐C4H4), the most stable isomer group contains the septet and the nonet isomers, which have three and four unpaired electrons on each Cr atoms, respectively. The dissociation energies indicate that the above [M(AIP)]2(μ‐C4H4) are as stable as the available [M(AIP)]2(μ‐C6H6). It would be a reasonable strategy using C4H4 as central ligand to induce the higher spin multiplicity of inverse sandwiches. [ABSTRACT FROM AUTHOR]

An asymmetric N -alkyl, N ′-aryl-β-diketiminate ligand L (L = 2-((S)-(-)-1-phenylethylimino)-4-(2,6-diisopropylphenylimido)pentane) was prepared. Synthesis of solvent-free chloro-bridged dimers, [LFe(μ-Cl)] 2 and [LCo(μ-Cl)] 2 are presented. Upon reduction in the presence of cis -cyclooctadiene, rare examples of low-valent complexes LFe(cod) and LCo(cod) were obtained. All metal complexes were fully characterized by 1 H NMR spectroscopy, elemental analysis, and X-ray crystallography. Crystallographic and spectroscopic results indicate that the N -alkyl, N ′-aryl-β-diketiminate ligand L is sterically smaller but a better electron donor than the N , N ′-diaryl-substituted β-diketiminate ligand L Me,Dipp (L Me,Dipp = 2,4-bis(2,6-diisopropylphenylimido)pentane). [ABSTRACT FROM AUTHOR]

• · N -Heterocyclic silylenes (NHSis) can be modified in both electronic and steric properties. • · N -Heterocyclic silylenes (NHSis) feature strong σ-donating character. • · N -Heterocyclic silylenes (NHSis) can be served as supporting ligands in low-valent main group chemistry. N -Heterocyclic silylenes (NHSis) are the silicon analogues of N -heterocyclic carbenes (NHCs), which feature a neutral divalent silicon atom directly bonded to at least one nitrogen atom in a heterocyclic framework. NHSis have long been utilized as versatile ligands in transition metal chemistry due to their strong σ-donating character. In recent years, significant progress has been achieved in the application of NHSis for the stabilization of low-valent main group element compounds, which allowed the synthesis and comprehensive reactivity study of these fascinating species. This review summarizes the recent achievements in this new and flourishing field, including synthetic approaches, structural features and reactivity of these NHSi-stabilized low-valent main group element compounds. [ABSTRACT FROM AUTHOR]

The inverse sandwiches [E-C5-nH5-nNn-E]+ and [E-C5-nH5-n-Pn-E]+ (n=1, 2, 3; E=Al, Ga, In, Tl) with low-valent boron group elements are studied. The (-5, -5) coordinated inverse sandwich [E-C5-nH5-nNn-E]+ is unstable in energy or nonexistent. However, the (-5, -5) coordinated [E-C5-nH5-n-Pn-E]+ is not only stable in energy, but also stable against dissociation. The dissoction stability [E-C5-nH5-n-Pn-E]+ with the same E element decreases as the number n increases, while for the certain n number, the dissociation energies with different E elements are close to each other. [E-C4H4P-E]+ has similar dissocition stability to the well-known [E-C5H5-E]+. The inteaction between C5-nH5-nPn and lowvalent E element is mainly ionic. Since lone pairs of electrons locate on both E and P atoms, the (-5, -5) coordinated inverse sandwich [E-C5-nH5-n-Pn-E]+ would act as multi electron-donors. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) spectroscopy is an extremely versatile technique for the characterisation of homogeneous catalysts involving paramagnetic centres. The paramagnetic parent pre-catalyst, the activated catalyst itself or any resulting reactive intermediates, can all be monitored in situ in order to delineate the role of the formal metal oxidation state and the influence of ligand structure on the resulting catalytic activity. In this review of our recent results, we describe how highly reactive, low valent transition metal complexes of formal oxidation states Ni(I), Fe(I) and Cr(I) coordinated by N-heterocyclic carbene (NHC) or phosphine ligands and which are active for a range of cross-coupling reactions or ethylene oligomerisation, have been investigated by EPR. Analysis of the EPR spectra revealed (i) how the influence of the NHC ring size affects the electronic properties of the Ni(I) centre, (ii) how low spin Fe(I) intermediates are catalytically competent on-cycle species in cross-coupling reactions and (iii) how intramolecular structural rearrangements involving Cr(I) centres occur following the addition of a co-catalyst to the reaction medium. These results demonstrate the utility of EPR to probe the structure-reactivity relationships in paramagnetic homogeneous catalysts, providing information not readily accessible by other techniques. [ABSTRACT FROM AUTHOR]

• Important recent development in synthesis of multiple bonded pnictogens (P, As, Sb, Bi). • Structure and bonding of dipnictenes. • Heavy main-group element based functionalities. • Electrochemical behavior and synthetic accessibility of stable radicals. • Coordination chemistry of dipnictenes. Dipnictenes are molecules comprising a double bond between two Group 15 elements (referred as pnictogens (Pn) = P, As, Sb, Bi). Over the last decades, the chemistry of dipnictenes has undergone a remarkable advance. This is largely because of the advancement of new ligand sets with distinct stereoelectronic properties. In general, classical dipnictenes are kinetically stabilized by the use of extremely bulky aryl or alkyl substituents. In recent years, numerous ligand frameworks featuring non-carbon donor substituents have also been introduced in dipnictenes chemistry. Now a plethora of dipnictenes with divergent electronic structure, reactivity, and physical properties are known. Among carbon-donor substituents, stable N-heterocyclic carbenes (NHCs) and other singlet carbenes have also been used as potent Lewis bases to derive related unsaturated species. A comprehensive understanding of the structure, bonding, and reactivity of a whole series of dipnictenes (RPn=PnR) (R = a substituent) as well as the influence of substituents on the nature of these species will be instrumental for the advancement of the field, in particular to unveil the relevance of these molecules in materials science. The aim of this review is to outline recent advances in dipnictene chemistry with a special focus on their reactivity. The outcomes show that dipnictenes have emerged from simple laboratory curiosities to versatile and useful synthons in modern main-group chemistry, which is expected to evolve further. [ABSTRACT FROM AUTHOR]

The chemistry of the low-valent Group 13 elements (E = B, Al, Ga, In, Tl) has formed the recent hot topic. Recently, a series of low-valent Group 13-based compounds have been synthesized, i.e., [E-Cp*-E]+ (E = Al, Ga, In, Tl) cations, which have been termed as the interesting 'inverse sandwich' complexes. To enrich the family of inverse sandwiches, we report our theoretical design of a new type of inverse sandwiches E-C4H4-E (E = Al, Ga, In, Tl) for stabilizing the low-valent Group 13 elements. The calculated dissociation energies indicate that unlike [E-Cp-E]+ that dissociates via loss of the charged atom E+, E-C4H4-E dissociates via loss of the neutral atom E with the bond strengths of Al > Ga > In > Tl. Moreover, E-C4H4-E are more stable in dissociation than [E-Cp-E]+ cations. By comparing with other various isomers, we found that the inverted E-C4H4-E should be kinetically quite stable with the least conversion barriers of 33.5, 33.5, 35.2, and 36.9 kcal/mol for E = Al, Ga, In, and Tl, respectively. Furthermore, replacement of cyclobutadiene-H atoms by the highly electron-positive groups such as SiH3 and Si(CH3)3 could significantly stabilize the inverted form in thermodynamics. Possible synthetic routes are proposed for E-C4H4-E. With no need of counterions, the newly designed neutral complexes E-C4H4-E welcome future synthesis. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: A series of all-metal dinuclear alkaline-earth metallocenes, M2(η5-E5)2 (M=Be, Mg, Ca; E=Sb, Bi), have been calculated by the density functional theory (DFT). Natural Bonding Orbital (NBO) analysis indicates that the metal–metal bonds of the title compounds are all single bonds with each metal in its +1 oxidation state, and the bonding between the metal and the all-metal ligand is mainly ionic. For both M2(η5-Sb5)2 and M2(η5-Bi5)2, the metal–ligand bonds are very strong and the lighter alkaline-earth metal has stronger metal–ligand bonding. By comparing the dissociation energies of metal–metal bond and metal–ligand bond for each M2(η5-E5)2, the single metal–metal bond is much weaker than the metal–ligand bond with the same metals. The Mg–Mg bond is the strongest in the M2(η5-Sb5)2 and M2(η5-Bi5)2 species. Nucleus-independent chemical shifts (NICS) values suggest the planar exhibits characteristics of aromaticity in these M2(η5-E5)2 species. All the NICS values decrease in the order of Be2(η5-E5)2 >Mg2(η5-E5)2 >Ca2(η5-E5)2 except for the NICS (1.0) values of the M2(η5-Bi5)2 (M=Be, Mg, Ca) species. The absolute values of NICS (0.0), NICS (0.5) and NICS (1.0) for M2(η5-Sb5)2 are larger than those of the corresponding M2(η5-Bi5)2. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis and molecular structure of the zero-valent platinum-mono-carbene-bis-alkene complexes [Pt0(NHC)(dimethyl fumarate)2] (NHC=1,3-dimesityl-imidazol-2-ylidene (1a); 1,3-dimesityl-dihydroimidazol-2-ylidene (2a); diphenyl-dihydroimidazol-2-ylidene (2b) are described. Two routes have been evaluated for the synthesis of 1a and 2a, involving reaction of a zero-valent platinum compound either with an isolated carbene ligand, or with an in situ generated carbene ligand. The in situ method proved to be easier and gave similar yields of about 50% after crystallization. Attempts have been made to synthesize similar compounds with N-phenyl and N-alkyl groups, of which the latter met with little success. However, (1,3-diphenyl-dihydroimidazol-2-ylidene)-bis(η2-dimethyl fumarate) platinum(0) (2b) could be obtained in 49% yield, after crystallization, from the appropriate Wanzlick dimer. Compound 1a reacts with H2 and D2 in sequences of oxidative addition, migration–insertion involving dimethyl fumarate, and reductive elimination to form neutral hydrido platinum (II) carbene complexes, probably containing a metallacyclic (R)–Csp="0.25" />…Pt unit. [Copyright &y& Elsevier]

• Synthesis and structural investigations of new O,N-heterocyclic germylene. • The insertion of low-valent metallylene into the S–S bond of inorganic disulfide. • Hirshfeld surface analysis for the study of intermolecular interactions in the crystal. Synthesis and single-crystal X-ray diffraction study (SC-XRD) of the O,N-heterocyclic germylene Ge(PhAp) (1) containing chelate 4,6-di-tert-butyl-N-phenyl-o-amidophenolate ligand (PhApH 2 , where Ap – o -amidophenolate) are reported. Germylene 1 demonstrates a monomeric structure in contrast to earlier known related stannylene Sn(PhAp) (2) existing as a dimer. Diverse weak intermolecular interactions (Ge...Ge, CH...π(chelate) and Ge...π(arene)) were detected in the crystal packing of germylene 1. Hirshfeld surface analysis has been performed to evaluate such interactions. Reactivity of compounds 1 and 2 towards dithiodiiron hexacarbonyl has been examined. Low-valent germanium(II) and tin(II) centers are readily inserted into S-S bond of dithiodiiron hexacarbonyl with the formation of Fe 4 (µ 4 -ES 4)(CO) 12 (E: Ge(3); Sn(4)) and bis-ligand complexes of tetravalent metals E(PhAp) 2. The resulting germanium(IV) and tin(IV) bis-o-amidophenolates were isolated as six-coordinated pyridine adducts E(PhAp) 2 (Py) 2 (E: Ge(5); Sn(6)). All complexes were characterized by SC-XRD. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The reactivity of dicoordinated Sn(0) compounds, stannylones, is probed using density functional theory (DFT)-based reactivity indices and compared with the reactivity of dicoordinated Sn(II) compounds, stannylenes. For the former compounds, the influence of different types of electron-donating ligands, such as cyclic and acyclic carbenes, stannylenes and phosphines, on the reactivity of the central Sn atom is analyzed in detail. Sn(0) compounds are found to be relatively soft systems with a high nucleophilicity, and the plots of the Fukui function f(-) for an electrophilic attack consistently predict the highest reactivity on the Sn atom. Next, complexes of dicoordinated Sn compounds with different Lewis acids of variable hardness are computed. In a first part, the double-base character of stannylones is demonstrated in interactions with the hardest Lewis acid H(+). Both the first and second proton affinities (PAs) are high and are well correlated with the atomic charge on the Sn atom, probing its local hardness. These observations are also in line with electrostatic potential plots that demonstrate that the tin atom in Sn(0) compounds bears a higher negative charge in comparison to Sn(II) compounds. Stannylones and stannylenes can be distinguished from each other by the partial charges at Sn and by various reactivity indices. It also becomes clear that there is a smooth transition between the two classes of compounds. We furthermore demonstrate both from DFT-based reactivity indices and from energy decomposition analysis, combined with natural orbitals for chemical valence (EDA-NOCV), that the monocomplexed stannylones are still nucleophilic and as reactive towards a second Lewis acid as towards the first one. The dominating interaction is a strong σ-type interaction from the Sn atom towards the Lewis acid. The interaction energy is higher for complexes with the cation Ag(+) than with the non-charged electrophiles BH(3), BF(3), and AlCl(3)., (Copyright © 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.)