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A systematic study to access stable stannaimines is reported, by combining different heteroleptic stannylenes with a range of organic azides. The reactions of terphenyl‐/hypersilyl‐substituted stannylenes yield the putative tin nitrogen double bond, but is directly followed by 1,2‐silyl migration to give SnII systems featuring bulky silylamido ligands. By contrast, the transition from a two σ donor ligand set to a mixed σ‐donor/π‐donor scaffold allows access to three new stannaimines which can be handled at room temperature. The reactivity profile of these Sn=N bonded species is crucially dependent on the substituent at the nitrogen atom. As such, the Sn=NMes (Mes=2,4,6‐Me3C6H2) system is capable of activating a broad range of substrates under ambient conditions via 1,2‐addition reactions, [2+2] and [4+2] cycloaddition reactions. Most interestingly, very rare examples of main group multiple bond metathesis reactions are also found to be viable. [ABSTRACT FROM AUTHOR]

A systematic study to access stable stannaimines is reported, by combining different heteroleptic stannylenes with a range of organic azides. The reactions of terphenyl‐/hypersilyl‐substituted stannylenes yield the putative tin nitrogen double bond, but is directly followed by 1,2‐silyl migration to give SnII systems featuring bulky silylamido ligands. By contrast, the transition from a two σ donor ligand set to a mixed σ‐donor/π‐donor scaffold allows access to three new stannaimines which can be handled at room temperature. The reactivity profile of these Sn=N bonded species is crucially dependent on the substituent at the nitrogen atom. As such, the Sn=NMes (Mes=2,4,6‐Me3C6H2) system is capable of activating a broad range of substrates under ambient conditions via 1,2‐addition reactions, [2+2] and [4+2] cycloaddition reactions. Most interestingly, very rare examples of main group multiple bond metathesis reactions are also found to be viable. [ABSTRACT FROM AUTHOR]

The N-heterocyclic olefin (NHO) ImMe4＝CH2 (2) (ImMe4＝CH2 = (MeCNMe)2C＝CH2) was employed for the synthesis of the titanium complex 3 derived from an NHO ligand precursor. By reacting 2 with the bis(π–η5:σ–η1-pentafulvene)titanium complex 1a, the terminal ylidic methylene unit of 2 is deprotonated by the quaternary exocyclic carbon atom of one pentafulvene ligand of 1a yielding the titanium complex 3 which bears an anionic NHO ligand (ImMe4＝CH−). 3 was characterized by NMR spectroscopy, single crystal X-ray diffraction and quantum chemical calculations. The latter highlight that 3 is best described as a titanium vinyl complex with significant contribution of the titanium alkylidene resonance structure. [ABSTRACT FROM AUTHOR]

By employing the highly reducing aluminyl complex [K{(NON)Al}]2 (NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene), we demonstrate the controlled formation of P42− and P44− complexes from white phosphorus, and chemically reversible inter‐conversion between them. The tetra‐anion features a unique planar π‐bonded structure, with the incorporation of the K+ cations implicit in the use of the anionic nucleophile offering additional stabilization of the unsaturated isomer of the P44−fragment. This complex is extremely reactive, acting as a source of P3−: exposure to ammonia leads to the release of phosphine (PH3) under mild conditions (room temperature and pressure), which contrast with those necessitated for the direct combination of P4 and NH3 (>5 kbar and >250 °C). [ABSTRACT FROM AUTHOR]

By employing the highly reducing aluminyl complex [K{(NON)Al}]2 (NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene), we demonstrate the controlled formation of P42− and P44− complexes from white phosphorus, and chemically reversible inter‐conversion between them. The tetra‐anion features a unique planar π‐bonded structure, with the incorporation of the K+ cations implicit in the use of the anionic nucleophile offering additional stabilization of the unsaturated isomer of the P44−fragment. This complex is extremely reactive, acting as a source of P3−: exposure to ammonia leads to the release of phosphine (PH3) under mild conditions (room temperature and pressure), which contrast with those necessitated for the direct combination of P4 and NH3 (>5 kbar and >250 °C). [ABSTRACT FROM AUTHOR]

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12–16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001. [ABSTRACT FROM AUTHOR]

Synthetic routes to lithium, magnesium, and zinc aluminyl complexes are reported, allowing for the first structural characterization of an unsupported lithium–aluminium bond. Crystallographic and quantum‐chemical studies are consistent with the presence of a highly polar Li−Al interaction, characterized by a low bond order and relatively little charge transfer from Al to Li. Comparison with magnesium and zinc aluminyl systems reveals changes to both the M−Al bond and the (NON)Al fragment (where NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene), consistent with a more covalent character, with the latter complex being shown to react with CO2 via a pathway that implies that the zinc centre acts as the nucleophilic partner. [ABSTRACT FROM AUTHOR]

Synthetic routes to lithium, magnesium, and zinc aluminyl complexes are reported, allowing for the first structural characterization of an unsupported lithium–aluminium bond. Crystallographic and quantum‐chemical studies are consistent with the presence of a highly polar Li−Al interaction, characterized by a low bond order and relatively little charge transfer from Al to Li. Comparison with magnesium and zinc aluminyl systems reveals changes to both the M−Al bond and the (NON)Al fragment (where NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene), consistent with a more covalent character, with the latter complex being shown to react with CO2 via a pathway that implies that the zinc centre acts as the nucleophilic partner. [ABSTRACT FROM AUTHOR]

The synthesis of the new bulky vinyllithium reagent (MeIPr=CH)Li, (MeIPr=[(MeCNDipp)2C]; Dipp=2,6‐iPr2C6H3) is reported. This vinyllithium precursor was found to act as a general source of the anionic 2σ, 2π‐electron donor ligand [MeIPr=CH]−. Furthermore, a high‐yielding route to the degradation‐resistant SiII precursor MeIPr⋅SiBr2 is presented. The efficacy of (MeIPr=CH)Li in synthesis was demonstrated by the generation of a complete inorganic divinyltetrelene series (MeIPrCH)2E: (E=Si to Pb). (MeIPrCH)2Si: represents the first two‐coordinate acyclic silylene not bound by heteroatom donors, with dual electrophilic and nucleophilic character at the SiII center noted. Cyclic voltammetry shows this electron‐rich silylene to be a potent reducing agent, rivalling the reducing power of the 19‐electron complex cobaltocene (Cp2Co). [ABSTRACT FROM AUTHOR]

Abstract: The introduction of the labile trimethylsiloxy group to GeII centers in the presence of an N‐heterocyclic carbene donor is reported. The new complex IPr⋅GeCl(OSiMe3) (IPr=[(HCNDipp)2C:]; Dipp=2,6‐iPr2C6H3) was readily converted into the structurally unique GeII siloxy(hydrido)germylene IPr⋅GeH(OSiMe3)⋅BH3 by treatment with lithium borohydride. Additionally, the reactive siloxygermylene cation [IPr⋅Ge(OSiMe3)]+ was synthesized and clean oxidative addition of CH2Cl2 was demonstrated. The two‐coordinate [IPr⋅Ge(OSiMe3)]+ cation also promoted the catalytic hydroborylation of sterically hindered ketones under mild conditions, with enhanced reactivity stemming from an open coordination site at Ge. [ABSTRACT FROM AUTHOR]

The recently reported bulky N-heterocyclic carbene ITr (ITr = [(HCNCPh3)2C:]) was found to stabilize low-coordinate Ag(i) environments. These electrophilic species were crystallographically identified as the weak solvates [(ITr)Ag(sol)]+ (sol = PhF, MesH or CH2Cl2) and as a solvent-free dimer [(ITr)Ag]22+. The highly electrophilic nature of the [(ITr)Ag]+ cation was further demonstrated by the calculation of a very high methyl ion affinity (MIA) and the synthesis of [(ITr)Ag(PCO)] which features substantial side-on electron donation from a P–C π bond to Ag. [ABSTRACT FROM AUTHOR]

The extremely bulky N-heterocyclic carbene (NHC), ITr (ITr=[(HCNCPh3)2C:]) featuring sterically shielding umbrella-shaped trityl (CPh3) substituents was prepared. This NHC features the highest percent buried volume (% Vbur) to date, and was used to form a thermally stable quasi one-coordinate thallium(I) cation [ITr-Tl]+. This TlI adduct and the corresponding lithium complex [ITr ⋅Li(OEt2)]+ are versatile 'all-in-one' transmetalation/ligation reagents for preparing low-coordinate inorganic species inaccessible by pre-existing routes. [ABSTRACT FROM AUTHOR]

Conspectus N-Heterocyclic olefins (NHOs) have gone from the topic of a few scattered (but important) reports in the early 1990s to very recently being a ligand/reagent of choice in the far-reaching research fields of organocatalysis, olefin and heterocycle polymerization, and low oxidation state main group element chemistry. NHOs are formally derived by appending an alkylidene (CR2) unit onto an N-heterocyclic carbene (NHC), and their pronounced ylidic character leads to high nucleophilicity and soft Lewis basic character at the ligating carbon atom. These olefinic donors can also be structurally derived from imidazole, triazole, and thiazole-based heterocyclic carbenes and, as a result, have highly tunable electronic and steric properties. In this Account, we will focus on various synthetic routes to imidazole-2-ylidene derived NHOs (sometimes referred to as deoxy-Breslow intermediates) followed by a discussion of the electron-donor ability of this structurally tunable ligand group. It should be mentioned that NHOs have a close structural analogy with Breslow-type intermediates, N-heterocyclic ketene aminals, and β-azolium ylides; while these latter species play important roles in advancing synthetic organic chemistry, discussion in this Account will be confined mostly to imidazole-2-ylidene derived NHOs. In addition, we will cover selected examples from the literature where NHOs and their anionic counterparts, N-heterocyclic vinylenes, are used to access reactive main group species not attainable using traditional ligands. Added motivation for these studies comes from the emerging number of low coordinate main group element based compounds that display reactivity once reserved for precious metal complexes (such as H-H and C-H bond activation). Moreover, NHOs are versatile precursors to new mixed element (P/C and N/C), and potentially bidentate, ligand constructs of great potential in catalysis, where various metal oxidation states and coordination environments need to be stabilized during a catalytic cycle. The most active area of recent growth for NHOs is their use as nucleophiles to promote efficient organocatalytic transformations, including transesterification, carbonyl reduction, and the conversion of CO2 into value added products. Polyesters have also been generated through the NHO-promoted ring-opening polymerization of lactones, and the highly tunable nature of NHO organocatalysts allows for the rapid screening and enhancement of catalytic performance. Therefore, the growing utility of NHOs in the realm of organic and polymer chemistry can be viewed as evidence of the widespread impact of N-heterocyclic olefins on the chemical community. It is hoped that through this Account others will join this flourishing research domain and that the rapid recent growth of NHO chemistry is sustained for the foreseeable future. [ABSTRACT FROM AUTHOR]

N-Heterocyclic carbene (NHC) complexes of Cd and Hg triflates (OTf) were prepared and their attempted conversion into rare cadmium and mercury hydrides was explored. In contrast to zinc, which forms stable [ZnH]+ complexes with NHCs, the heavier Cd and Hg congeners could not be formed; the increased instability of Cd-H and Hg-H units was rationalized with the aid of computations. It was also discovered that the dimeric adduct [IPr⋅Cd(μ-OTf)2]2 (IPr=[(HCNDipp)2C:]; Dipp=2,6- iPr2C6H3) is an active precatalyst for the hydrosilylation and hydroborylation of hindered aldehydes and ketones. The related zinc congener was inactive as a catalyst highlighting a distinct advantage of using heavy Group 12 metals to promote catalytic hydrosilylation/borylation. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a novel dimeric N-heterocyclic carbene ligated trimercury hexachloride adduct [(IPr)Hg3Cl6]2 [IPr = (HCNDipp)2C:; Dipp = 2,6- iPr2C6H3] is reported from the disproportionation reaction of IPr with mercury(I) chloride. The molecular structure of this species in the solid state represents a new bonding motif for a mercury halide. [ABSTRACT FROM AUTHOR]

A theoretical study of the desorption of hydrogen from rhombic Group 1 metal hydride dimers reveals a concerted reorganisation of the electron density for the M -H and H -H moieties as the reaction coordinate is traversed and a closed-shell H...H interaction evolves into a covalent H2 bond. The central role played by homopolar dihydrogen bonding in this process is revealed and analysed. [ABSTRACT FROM AUTHOR]

Bimetallic compounds containing direct metal‐group 13 element bonds have been shown to display unprecedented patterns of cooperative reactivity towards small molecules, which can be influenced by the identity of the group 13 element. In this context, we present here a systematic appraisal of group 13 metallo‐ligands of the type [(NON)E]− (NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene) for E=Al, Ga and In, through a comparison of structural and spectroscopic parameters associated with the trans L or X ligands in linear d10 complexes of the types LM{E(NON)} and XM′{E(NON)}. These studies are facilitated by convenient syntheses (from the In(I) precursor, InCp) of the potassium indyl species [{K(NON)In}⋅KCp]n (1) and [(18‐crown‐6)2K2Cp] [(NON)In] (1′), and lead to the first structural characterisation of Ag−In and Hg−E (E=Al, In) covalent bonds. The resulting structural, spectroscopic and quantum chemical probes of Ag/Hg complexes are consistent with markedly stronger σ‐donor capabilities of the aluminyl ligand, [(NON)Al]−, over its gallium and indium counterparts. [ABSTRACT FROM AUTHOR]

Bimetallic compounds containing direct metal‐group 13 element bonds have been shown to display unprecedented patterns of cooperative reactivity towards small molecules, which can be influenced by the identity of the group 13 element. In this context, we present here a systematic appraisal of group 13 metallo‐ligands of the type [(NON)E]− (NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene) for E=Al, Ga and In, through a comparison of structural and spectroscopic parameters associated with the trans L or X ligands in linear d10 complexes of the types LM{E(NON)} and XM′{E(NON)}. These studies are facilitated by convenient syntheses (from the In(I) precursor, InCp) of the potassium indyl species [{K(NON)In}⋅KCp]n (1) and [(18‐crown‐6)2K2Cp] [(NON)In] (1′), and lead to the first structural characterisation of Ag−In and Hg−E (E=Al, In) covalent bonds. The resulting structural, spectroscopic and quantum chemical probes of Ag/Hg complexes are consistent with markedly stronger σ‐donor capabilities of the aluminyl ligand, [(NON)Al]−, over its gallium and indium counterparts. [ABSTRACT FROM AUTHOR]

Bimetallic compounds containing direct metal‐group 13 element bonds have been shown to display unprecedented patterns of cooperative reactivity towards small molecules, which can be influenced by the identity of the group 13 element. In this context, we present here a systematic appraisal of group 13 metallo‐ligands of the type [(NON)E]− (NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene) for E=Al, Ga and In, through a comparison of structural and spectroscopic parameters associated with the trans L or X ligands in linear d10 complexes of the types LM{E(NON)} and XM′{E(NON)}. These studies are facilitated by convenient syntheses (from the In(I) precursor, InCp) of the potassium indyl species [{K(NON)In}⋅KCp]n (1) and [(18‐crown‐6)2K2Cp] [(NON)In] (1′), and lead to the first structural characterisation of Ag−In and Hg−E (E=Al, In) covalent bonds. The resulting structural, spectroscopic and quantum chemical probes of Ag/Hg complexes are consistent with markedly stronger σ‐donor capabilities of the aluminyl ligand, [(NON)Al]−, over its gallium and indium counterparts. [ABSTRACT FROM AUTHOR]

Abstract: Invited for the cover of this issue is the group of Eric Rivard at the University of Alberta and colleagues in Kyoto University (Norihiro Tokitoh group). The image depicts a low coordinate germanium complex, which was used to induce the catalytic reduction of ketones to value added products. Read the full text of the article at 10.1002/chem.201802958. [ABSTRACT FROM AUTHOR]