Germanium(II) Dithiolene Complexes

The 1 : 2 reaction of the imidazole-based dithiolate (2) with GeCl2  • dioxane in THF/TMEDA gives 3, a TMEDA-complexed dithiolene-based germylene. Compound 3 is converted to monothiolate-complexed (5) and N-heterocyclic carbene-complexed (7) germanium(II) dithiolene complexes via Lewis base ligand exchange. A bis-dithiolene-based germylene (8), involving a 3c-4e S-Ge-S bond, has also been synthesized through controlled hydrolysis of 7. The bonding nature of 3, 5, and 8 was investigated by both experimental and theoretical methods.

Synthesis, spectroscopic and structural properties of Sn(II) and Pb(II) triflate complexes with soft phosphine and arsine coordination

Reaction of the divalent M(OTf)₂ (M = Sn, Pb; OTf = CF₃SO₃) with soft phosphine and arsine ligands, L, where L = o-C₆H₄(ER₂)₂ (E = P, R = Me or Ph; E = As, R = Me), MeC(CH₂ER₂)₃ (E = P, R = Ph; E = As, R = Me), PhP(CH₂CH₂PPh₂)₂ or P(CH₂CH₂PPh₂)₃, affords complexes of stoichiometry M(L)(OTf)₂ as white powders, which have been characterised via elemental analysis, ¹H, ¹⁹F{¹H}, ³¹P{¹H} and ¹¹⁹Sn NMR spectroscopy, with the expected ³¹P-¹¹⁹Sn and ³¹P-²⁰⁷Pb couplings clearly evident. The crystal structures of nine of these pnictine complexes are reported, in each case revealing retention of one or both OTf anions, which gives rise to a diverse range of coordination environments including monomers, as well as varying degrees of oligomerisation to form weakly associated (OTf-bridged) dimers, trimers and polymers. ¹⁹F{¹H} NMR spectra indicate that the OTf is essentially anionic (dissociated) in solution. Anion metathesis of [M(OTf)₂{MeC(CH₂PPh₂)₃}] with Na[BAr^F] (BAr^F = B{3,5-(CF₃)₂C₆H₃}₄) yields the corresponding [M{MeC(CH₂PPh₂)₃}][BAr^F]₂ salts, the crystal structures of all three (M = Ge, Sn, Pb) reveal pyramidal dications with discrete [BAr^F]^- anions providing charge balance. Density functional theory (DFT) calculations on these [M{MeC(CH₂PPh₂)₃}]²⁺ (M = Ge, Sn, Pb) dications using the B3LYP-D3 functional show the presence of a directional lone pair, which is a mixture of valence s and p_z character, with the valence p-orbital character decreasing down group 14. Natural bond orbital (NBO) analysis also shows that the natural charge at the metal centre increases and the charge on the P centre decreases upon going down group 14.

Chemistry of the Bis(imine)-Based Tetradentate Ligand Stabilized Group 14 E(II) Cations (E=Ge and Sn)

The ambiphilic Ge(II) and Sn(II) cationic species have been reported to be isolated through kinetic or thermodynamic stabilizations. Nonetheless, steric congestion or excessive coordination of donor atoms to the cationic center concurrently disfavors its prompt reactivity. Our research in this field revolves around the utilization of structurally non-rigid bis(imine) based tetradentate supporting ligands for the stabilization of Ge(II) and Sn(II) cationic species. Such E(II) cationic systems have been advantaged due to inherent flexibility present at the ligand backbone allowing disposal of E(II) orbitals through geometric rearrangements for further reactivity. The bifunctionality present in the ligand enables the first examples of Ge(II) bis-monocations. Furthermore, the redox-active nature of the ligand encourages participation in chemical transformations. In this personal account we have provided a detailed discussion of our published work in this direction in the last five years.

Cooperative N-H bond activation by amido-Ge(ii) cations

N-heterocyclic carbene (NHC) and tertiary phosphine-stabilized germylium-ylidene cations, [R(L)Ge:]+, featuring tethered amido substituents at R have been synthesized via halide abstraction. Characterization in the solid state by X-ray crystallography shows these systems to be monomeric, featuring a two-coordinate C,N- or P,N-ligated germanium atom. The presence of the strongly Lewis acidic cationic germanium centre and proximal amide function allows for facile cleavage of N-H bonds in 1,2-fashion: the products resulting from reactions with carbazole feature a tethered secondary amine donor bound to a three-coordinate carbazolyl-GeII centre. In each case, addition of the components of the N-H bond occurs to the same face of the germanium amide function, consistent with a coordination/proton migration mechanism. Such as sequence is compatible with the idea that substrate coordination via the pπ orbital at germanium reduces the extent of N-to-Ge π donation from the amide, thereby enhancing the basicity of the proximal N-group.

Ge(ii) cation catalyzed hydroboration of aldehydes and ketones

The catalytic utility of a germylene cation 4 is reported. In the presence of compound 4, a variety of aldehydes and ketones can be hydroborylated using HBpin.

Cationic 2,2′-bipyridine complexes of germanium(ii) and tin(ii)

Tetrel analogues of transition metal complexes.

Reactive p-block cations stabilized by weakly coordinating anions

The chemistry of the p-block elements is a huge playground for fundamental and applied work. With their bonding from electron deficient to hypercoordinate and formally hypervalent, the p-block elements represent an area to find terra incognita. Often, the formation of cations that contain p-block elements as central ingredient is desired, for example to make a compound more Lewis acidic for an application or simply to prove an idea. This review has collected the reactive p-block cations (rPBC) with a comprehensive focus on those that have been published since the year 2000, but including the milestones and key citations of earlier work. We include an overview on the weakly coordinating anions (WCAs) used to stabilize the rPBC and give an overview to WCA selection, ionization strategies for rPBC-formation and finally list the rPBC ordered in their respective group from 13 to 18. However, typical, often more organic ion classes that constitute for example ionic liquids (imidazolium, ammonium, etc.) were omitted, as were those that do not fulfill the - naturally subjective -"reactive"-criterion of the rPBC. As a rule, we only included rPBC with crystal structure and only rarely refer to important cations published without crystal structure. This collection is intended for those who are simply interested what has been done or what is possible, as well as those who seek advice on preparative issues, up to people having a certain application in mind, where the knowledge on the existence of a rPBC that might play a role as an intermediate or active center may be useful.

Facile access to a Ge(ii) dication stabilized by isocyanides

The reaction of 2,6-dimethylphenylisocyanide with GeCl₂ afforded a Ge(ii) dication, which is stabilized by four isonitrile ligands through σ-donation.

Isolation of a germanium(ii) cation and a germylene iron carbonyl complex utilizing an imidazolin-2-iminato ligand

A novel amino(imino)germylene was synthesised. Its conversion with B(C₆F₅)₃ afforded a cyclic germanium(ii) cation in a methyl abstraction and ring closing reaction. The conversion with Fe₂(CO)₉ furnished a germylene iron carbonyl complex.

Cations and dications of heavier group 14 elements in low oxidation states

This review gives an introduction to the synthesis, properties, and reactivity of the cations and dications of the heavier group 14 elements in their low oxidation state.

The preparation and structure of Ge3F8 - a new mixed-valence fluoride of germanium, a convenient source of GeF2

The new binary mixed-valence fluoride of germanium, Ge3F8, has been obtained by heating GeF4 with powdered Ge in an autoclave (390 K/4 bar/48 h). The structure contains pyramidal Ge(II)F3 and octahedral Ge(IV)F6 units, linked by fluoride bridges. The new compound is the missing member of the series (GeF2)n·GeF4 (n = 2, 4, or 6). Sublimation of (GeF2)n·GeF4in vacuo provides a convenient source of GeF2 in ca. 30% overall yield.

Halometallate complexes of germanium(II) and (IV): probing the role of cation, oxidation state and halide on the structural and electrochemical properties

The Ge(IV) chlorometallate complexes, [EMIM]2 [GeCl6 ], [EDMIM]2 [GeCl6 ] and [PYRR]2 [GeCl6 ] (EMIM=1-ethyl-3-methylimidazolium; EDMIM=2,3-dimethyl-1-ethylimidazolium; PYRR=N-butyl-N-methylpyrrolidinium) have been synthesised and fully characterised; the first two also by single-crystal X-ray diffraction. The imidazolium chlorometallates exhibited significant CH⋅⋅⋅Cl hydrogen bonds, resulting in extended supramolecular assemblies in the solid state. Solution (1) H NMR data also showed cation-anion association. The synthesis and characterisation of Ge(II) halometallate salts [EMIM][GeX3 ] (X=Cl, Br, I) and [PYRR][GeCl3 ], including single-crystal X-ray analyses for the homologous series of imidazolium salts, are reported. In these complexes, the intermolecular interactions are much weaker in the solid state and they appear not to be significantly associated in solution. Cyclic-voltammetry experiments on the Ge(IV) species in CH2 Cl2 solution showed two distinct, irreversible reduction waves attributed to Ge(IV) -Ge(II) and Ge(II) -Ge(0) , whereas the Ge(II) species exhibited one irreversible reduction wave. The potential for the Ge(II) -Ge(0) reduction was unaffected by changing the cation, although altering the oxidation state of the precursor from Ge(IV) to Ge(II) does have an effect; for a given cation, reduction from the [GeCl3 ](-) salts occurred at a less cathodic potential. The nature of the halide co-ligand also has a marked influence on the reduction potential for the Ge(II) -Ge(0) couple, such that the reduction potentials for the [GeX3 ](-) salts become significantly less cathodic when the halide (X) is changed Cl→Br→I.

The tipping point of the inert pair effect: experimental and computational comparison of In(I) and Sn(II) bis(imino)pyridine complexes

The autoionization reaction of neutral bis(imino)pyridine and SnX2 led to three compounds [{ArN[double bond, length as m-dash]CPh}2(NC5H3)]SnX(+)SnX3(-) (Ar = 2,6-(2,5-(t)Bu2C6H3), X = Cl, Br; Ar = 2,6-(2,6-Me2C6H3), X = Cl) which display, within the same species, cations and anions possessing Sn(ii) centers. Computational analysis compared the ligated Sn(ii) cations with bis(imino)pyridine In(i) complexes that showed unprecedented weak metal-ligand covalent interactions, consistent with the In(i) 5s(2) electrons remaining as an inert nonbonding pair. Analysis of the metal-ligand bonding indicates that the chloride ligand of the Sn(ii) complex induces promotion of the metal 5s(2) electron pair to a stereochemically active hybridized orbital, which, in turn, allows strong coordination of the bis(imino)pyridine to Sn.

A cyclic germadicarbene ("germylone") from germyliumylidene

By employing the chelate dicarbene 1, the new chlorogermyliumylidene complex 2 could be synthesized and isolated in 95% yield. Dechlorination of 2 with sodium naphthalenide furnishes the unique cyclic germadicarbene 3 which could be isolated in 45% yield. Compound 3 is the first isolable Ge(0) complex with a single germanium atom stabilized by a dicarbene. Its molecular structure is in accordance with DFT calculations which underline the peculiar electronic structure of 3 with two lone pairs of electrons at the Ge atom.