Expanding the Steric Coverage Offered by Bis(amidosilyl) Chelates: Isolation of Low-Coordinate N-Heterocyclic Germylene Complexes

Recent advances in the chemistry of isolable carbene analogues with group 13-15 elements

Carbenes (R2C:), compounds with a divalent carbon atom containing only six valence shell electrons, have evolved into a broader class with the replacement of the carbene carbon or the RC moiety with main group elements, leading to the creation of main group carbene analogues. These analogues, mirroring the electronic structure of carbenes (a lone pair of electrons and an empty orbital), demonstrate unique reactivity. Over the last three decades, this area has seen substantial advancements, paralleling the innovations in carbene chemistry. Recent studies have revealed a spectrum of unique carbene analogues, such as monocoordinate aluminylenes, nitrenes, and bismuthinidenes, notable for their extraordinary properties and diverse reactivity, offering promising applications in small molecule activation. This review delves into the isolable main group carbene analogues that are in the forefront from 2010 and beyond, spanning elements from group 13 (B, Al, Ga, In, and Tl), group 14 (Si, Ge, Sn, and Pb) and group 15 (N, P, As, Sb, and Bi). Specifically, this review focuses on the potential amphiphilic species that possess both lone pairs of electrons and vacant orbitals. We detail their comprehensive synthesis and stabilization strategies, outlining the reactivity arising from their distinct structural characteristics.

On the edge of the steric repulsion and reactivity of bulky anilines; a case study of chloro(imino)phosphine synthesis

2-Benzhydryl-4-methyl-6-(1,1'-diphenyl-2-phenyl-ethyl)aniline was prepared by a three-step process. 2,6-Bis(benzhydryl)-4-methyl-aniline was protected by Schiff coupling, then benzylated and finally dealkylated by using hydrochloric acid and methanol. The resulting compound exhibits one of the highest buried volumes around the nitrogen atom of anilines prepared so far, but it reacts with phosphorus trichloride and triethylamine to give a monomeric chloro(imino)phosphine.

Mono- and Dinuclear Aluminium Complexes Derived from Biguanide and Carbothiamide Ligands

Dianionic N,N-chelating ligands play a crucial role in coordination chemistry, but reports on related complexes remain limited to certain types of ligands. In here, the reactions of two diprotic ligands, i.e., a biguanide and a carbothiamide, with trimethylaluminium, are reported, which give rise to mono- and dinuclear aluminium(III) complexes. In addition, single deprotonation of the diprotic biguanide using potassium bis(trimethylsilyl)amide gives rise to a one-dimensional coordination polymer. All complexes have been fully characterized, and their solid-state structures were determined by single crystal X-ray diffraction analysis.

Chloropentaphenyldisiloxane—Model Study on Intermolecular Interactions in the Crystal Structure of a Monofunctionalized Disiloxane

Small functional siloxane units have gained great interest as molecular model systems for mimicking more complex silicate structures both in nature and in materials chemistry. The crystal structure of chloropentaphenyldisiloxane, which was synthesized for the first time, was elucidated by single-crystal X-ray diffraction analysis. The molecular crystal packing was studied in detail using state-of-the-art Hirshfeld surface analysis together with a two-dimensional fingerprint mapping of the intermolecular interactions. It was found that the phenyl C–H bonds act as donors for both weak C–H···π and C–H···Cl hydrogen bond interactions. The influence of intramolecular Si–O–Si bond parameters on the acceptor capability of functional groups in intermolecular hydrogen bond interactions is discussed.

Synthetic, structural and reaction chemistry of N-heterocyclic germylene and stannylene compounds featuring N-boryl substituents

This study details the syntheses of N-heterocyclic germylenes and stannylenes featuring diazaborolyl groups, {(HCDippN)₂B} (Dipp = 2,6-ⁱPr₂C₆H₃), as both of the N-bound substituents, with a view to generating electron rich and sterically protected metal centres. The energies of their key frontier orbitals - the group 14-centred lone pair and orthogonal p_π-orbital (typically the HOMO-2 and LUMO) have been probed by DFT calculations and compared with a related acyclic analogue, revealing (in the case of the stannylenes) a correlation with the measured ¹¹⁹Sn chemical shifts. The reactivity of the germylene systems towards oxygen atom transfer agents has been examined, with 2 : 1 reaction stoichiometries being observed for both Me₃NO and pyridine N-oxide, leading to the formation of products thought to be derived from the activation of C-H bonds by a transient first-formed germanone.

Accessing Low-Valent Inorganic Cations by Using an Extremely Bulky N-Heterocyclic Carbene

The extremely bulky N-heterocyclic carbene (NHC), ITr (ITr=[(HCNCPh₃ )₂ C:]) featuring sterically shielding umbrella-shaped trityl (CPh₃ ) substituents was prepared. This NHC features the highest percent buried volume (%V_bur ) to date, and was used to form a thermally stable quasi one-coordinate thallium(I) cation [ITr-Tl]⁺ . This Tl^I 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.

Basic Reactivity Pattern of a Cyclic Disilylated Germylene

In order to estimate the reactivity of disilylated germylene phosphine adducts, a cyclic version of this compound class was reacted with a number of different reagents. Reactions with the chalcogens sulfur, selenium, and tellurium led to dimers of the heavy ketone analogues. Reactions with water and ethyl bromide proceeded to give the respective oxidized germanol and germyl bromide. Two different reactions with alkynes were observed which led either to a germacyclopropene, by addition of tolane to the germylene, or to a silagermacyclobutene, likely formed by addition of the alkyne across a silagermene. Reaction via the silagermene was also observed in the reaction with benzophenone. Reaction of a germylene phosphine adduct with GeCl2·(dioxane) provided insertion of the silylated germylene into a Ge-Cl bond, leading to a germylated chlorogermylene phosphine adduct.

Isolation of a Cyclic (Alkyl)(amino)germylene

A 1,4-addition of a dichlorogermylene dioxane complex with α,β-unsaturated imine 1 gave a dichlorogermane derivative 2 bearing a GeC₃N five-membered ring skeleton. By reducing 2 with KC₈, cyclic (alkyl)(amino)germylene 3 was synthesized and fully characterized. Germylene 3 readily reacted with TEMPO, N₂O and S₈, producing the 1:2 adduct 4, the oxo-bridged dimer 5 and the sulfido-bridged dimer 6, respectively.

A Systematic Study of Structure and E-H Bond Activation Chemistry by Sterically Encumbered Germylene Complexes

A series of new germylene compounds has been synthesized offering systematic variation in the σ- and π-capabilities of the α-substituent and differing levels of reactivity towards E-H bond activation (E=H, B, C, N, Si, Ge). Chloride metathesis utilizing [(terphenyl)GeCl] proves to be an effective synthetic route to complexes of the type [(terphenyl)Ge(ERn )] (1-6: ERn =NHDipp, CH(SiMe3 )2 , P(SiMe3 )2 , Si(SiMe3 )3 or B(NDippCH)2 ; terphenyl=C6 H3 Mes2 -2,6=Ar(Mes) or C6 H3 Dipp2 -2,6=Ar(Dipp) ; Dipp=C6 H3 iPr2 -2,6, Mes=C6 H2 Me3 -2,4,6), while the related complex [{(Me3 Si)2 N}Ge{B(NDippCH)2 }] (8) can be accessed by an amide/boryl exchange route. Metrical parameters have been probed by X-ray crystallography, and are consistent with widening angles at the metal centre as more bulky and/or more electropositive substituents are employed. Thus, the widest germylene units (θ>110°) are found to be associated with strongly σ-donating boryl or silyl ancillary donors. HOMO-LUMO gaps for the new germylene complexes have been appraised by DFT calculations. The aryl(boryl)-germylene system [Ar(Mes) Ge{B(NDippCH)2 }] (6-Mes), which features a wide C-Ge-B angle (110.4(1)°) and (albeit relatively weak) ancillary π-acceptor capabilities, has the smallest HOMO-LUMO gap (119 kJ mol(-1) ). These features result in 6-Mes being remarkably reactive, undergoing facile intramolecular C-H activation involving one of the mesityl ortho-methyl groups. The related aryl(silyl)-germylene system, [Ar(Mes) Ge{Si(SiMe3 )3 }] (5-Mes) has a marginally wider HOMO-LUMO gap (134 kJ mol(-1) ), rendering it less labile towards decomposition, yet reactive enough to oxidatively cleave H2 and NH3 to give the corresponding dihydride and (amido)hydride. Mixed aryl/alkyl, aryl/amido and aryl/phosphido complexes are unreactive, but amido/boryl complex 8 is competent for the activation of E-H bonds (E=H, B, Si) to give hydrido, boryl and silyl products. The results of these reactivity studies imply that the use of the very strongly σ-donating boryl or silyl substituents is an effective strategy for rendering metallylene complexes competent for E-H bond activation.

Synthesis and reactivity of a germylene stabilized by a boraguanidinate ligand

The reactivity of a germylene stabilized by a boraguanidinate ligand with various reagents is reported.

Concise access to iminophosphonamide stabilized heteroleptic germylenes: chemical reactivity and structural investigation

A heteroleptic three coordinate germylene monochloride, its adduct with a Lewis acid, and germaacid-chloride & -ester derivatives with sulfur and selenium have been reported.

Germylenes and stannylenes stabilized within N2PE rings (E = Ge or Sn): combined experimental and theoretical study

Bis(amino)phosphanes were shown to be excellent easily accessible precursors for the preparation of a variety of tetrylenes that significantly differ in their structures.

Mixed guanidinato-amido Ge(iv) and Sn(iv) complexes with GeE (E = S, Se) double bond and SnS4, Sn2Se2 rings

The oxidative addition of chalcogens (S and Se) to the guanidinate supported Ge(ii) and Sn(ii) amide complexes.

Synthesis, characterisation, and dehydrocoupling ability of zirconium complexes bearing hindered bis(amido)silyl ligands

Herein we detail the synthesis and characterisation of a series of zirconium compounds featuring the bis(amido)silyl ligand [(i)Pr2Si(NDipp)2](2-) (Dipp = 2,6-diisopropylphenyl). The functionalisation of bis(amido)silyl zirconium halide complexes with a variety of nucleophiles, such as LiNMe2, LiBH4 and MeLi, was explored and the resulting products showed a propensity to form anionic zirconate salts when the syntheses were carried out in THF. One of the zirconate products, [(i)Pr2Si(NDipp)2]Zr(NMe2)2·ClLi(THF)3, has the ability to catalyse the dehydrocoupling of primary and secondary amine-boranes at room temperature in aromatic solvents.

2-Adamantylidene and its heavier analogues: hyperconjugation versus lone pair stability and electrophilicity versus nucleophilicity

Too heavy to bend: The Cieplak-type hyperconjugative interaction mainly contributes to the stability of 2C and 2Si whereas the inertness of lone pairs is the major factor for 2Ge and 2Sn. These molecules (2X; X = C–Sn) can be classified as a class of ambiphilic compounds.