Facile Synthesis of an Octagermacubane with Two Three-Coordinate Germanium(0) Atoms and its Unique Radical Anion

Thermolysis of a 1 : 1 mixture of tris(di-tert-butylmethylsilyl)germane 9 and bis(di-tert-butylmethylsilyl)germane 17 at 100 °C produces unexpectedly octagermacubane 18 , having two 3-coordinate Ge⁰ atoms (40 % yield). 18 was characterized by X-ray crystallography and it is a singlet biradical (according to DFT quantum mechanical calculations and the absence of an EPR signal). Reactions of 18 with CH₂Cl₂ and H₂O yield the novel dichloro-octagermacubane 24 and hydroxy-octagermacubane 25 , respectively. Reduction of 18 with tBuMe₂SiNa in THF produces an isolable octagermacubane radical anion 26-Na . Based on X-ray crystallography, EPR spectroscopy and DFT quantum mechanical calculations, 26-Na is classified as a Ge-centered radical anion.     

Amidinate bromogermylene resulting from carbodiimide insertion into Ar–GeBr bond

The reaction of diaryldibromodigermene Tbb(Be)Ge = Ge(Br)Tbb (Tbb = 4-Bu^t-2,6-[CH(SiMe₃)₂]₂C₆H₂) with N,N'-diisopropyl-carbodiimide afforded the corresponding amidinato-supported bromogermylene via the insertion of the C=N moiety into the Ge–C(Tbb) sss-bond. The formation mechanism of the amidinato-supported bromogermylene was revealed by DFT calculations. This type of insertion reaction toward a metal–carbon bond can be interpreted in analogy to the reactivity of transition-metal complexes.     

Novel germylenes and stannylenes based on pyridine-containing dialcohol ligands

The reactions between M[N(SiMe₃)₂]₂ (M = Ge, Sn) and three pyridine-based dialcohols yielded germylenes and stannylenes 1-6. The composition and structures of the novel compounds were established by elemental analyses, ¹H and ¹³C NMR spectroscopy. The structures of insoluble species were confirmed by conversion to the corresponding dibromides 7-9. The single crystal structures of stannylene 4 and germylene 5 were determined by X-ray diffraction analyses. The germanium compound was found to be monomeric whilst the tin compound is a dimer. Both compounds possess strong transannular MN interaction in the solid phase.     

Reactivity of an N,N‐Chelated Germylene Toward Substituted Alkynes,Alkenes, and Allenes

Treatment of N,N‐chelated germylene [(iPr)₂NB(N‐2,6‐Me₂C₆H₃)₂]Ge ( 1 ) with ferrocenyl alkynes containing carbonyl functionalities, FcC≡CC(O)R, resulted in [2+2+2] cyclization and formation of the respective ferrocenylated 3‐Fc‐4‐C(O)R‐1,2‐digermacyclobut‐3‐enes 2 – 4 [R = Me ( 2 ), OEt ( 3 ) and NMe₂ ( 4 )] bearing intact carbonyl substituents. In contrast, the reaction between 1 and PhC(O)C≡CC(O)Ph led to activation of both C≡C and C=O bonds producing bicyclic compound containing two five‐membered 1‐germa‐2‐oxacyclopent‐3‐ene rings sharing one C–C bond, 4,8‐diphenyl‐3,7‐dioxa‐2,6‐digermabicyclo[3.3.0]octa‐4,8‐diene ( 5 ). With N‐methylmaleimide containing an analogous C(O)CH=CHC(O) fragment, germylene 1 reacted under [2+2+2] cyclization involving the C=C double bond, producing 1,2‐digermacyclobutane 6 with unchanged carbonyl moieties. Finally, 1 selectively added to the terminal double bond in allenes CH₂=C=CRR′ giving rise to 3‐(=CRR′)‐1,2‐digermacyclobutanes [R/R′ = Me/Me ( 7 ), H/OMe ( 8 )] bearing an exo‐C=C double bond. All compounds were characterized by ¹H, ¹³C{¹H} NMR, IR and Raman spectroscopy and the molecular structures of 3 , 4 , 5 , and 8 were established by single‐crystal X‐ray diffraction analysis. The redox behavior of ferrocenylated derivatives 2 – 4 was studied by cyclic voltammetry.     

Germylene and stannylene (Me2NCH2CH2O)2E as strong σ-donor ligands for transition metal complexes [ML(CO)n] (E = Ge, Sn; M = Cr, Mo, W, n = 4 or 5; M = Fe, n = 4). Synthesis, spectroscopic and theoretical study

A series of germylene and stannylene (Me₂NCH₂CH₂O)₂E (E = Ge, 1; E = Sn, 2) complexes of group 6 metals and iron carbonyls L·M(CO)_n (M = Cr, Mo, W, n = 5 (3-8), n = 4 (9, 10); M = Fe, n = 4 (11, 12)) were prepared. These complexes were characterized by ¹H, ¹³C NMR, FTIR and elemental analysis. Ligand properties of 1 and 2 were compared to PPh₃ and dmiy (N,N′-dimethylimidazolin-2-ylidene) using theoretical calculations (PBE/TZ2P) and FTIR. Ligand dissociation energies increase in the order Ph₃P < 2∼1 < dmiy, while donor strength rise in the order PPh₃ < dmiy < 2 < 1.     

Singlet-triplet energy separations in divalent five-membered cyclic conjugated C5H3X, C4H3SiX, C4H3GeX, C4H3SnX, and C4H3PbX (X = H, F, Cl, and Br)

Singlet-triplet energy gaps in cyclopenta-2,4-dienylidene, as well as its 2- or 3-halogenated derivatives, are compared and contrasted with their sila, germa, stana, and plumba analogues; at HF/6-31G* and B3LYP/ 6-311++G(3df, 2p) levels of theory. Energy gaps (ΔG_t-s), between triplet (t) and singlet (s) states, appear linearly proportional to: (i) the size of the group 14 divalent element (M = C, Si, Ge, Sn and Pb), (ii) the angle ∠C-M-C, and (iii) the ΔG_(LUMO-HOMO) of the singlet state involved. The magnitude of ΔG_t-s, for each 2- and/or 3-substituted species studied, increases with an order of: carbenes < silylenes < germylenes < stanylenes < plumbylenes. This order reverses for the barriers of the ring puckering. The puckering occurs with more ease for every singlet, compared to its corresponding triplet form.Regardless of the group 14 element (M) employed, every 3-halo-substituted species is more stable than the corresponding 2-halo-substituted isomer. For M = Pb, Sn and/or Ge; 3-halo-substituted species have higher ΔG_t-s than their corresponding 2-halo-substituted analogues. For M = Si, similar ΔG_t-s are found for 2- and 3-halogenated isomers. For M = C, 3-halo-substituted species have lower ΔG_t-s than their corresponding 2-halo-substituted analogues.Every cyclic singlet has a larger ∠C-M-C angle, than its corresponding cyclic triplet state, except for 3-halosilacyclopenta-2,4-dienylidenes where triplet has a larger ∠C-M-C angle than its corresponding singlet state.     

Phosphinohydrazines and phosphinohydrazides M(-N(R)-N(R)-PPh2)n of some transition and main group metals: synthesis and characterization: Rearrangement of Ph2P-NR-NR- ligands into aminoiminophosphorane, RNPPh2-NR-, and related chemistry

The reactions of phosphinohydrazines ArNH-N(Ar)-PPh₂ {Ar = Ph (2a), p-Bu^t-C₆H₄- (2b)} with metal silylamides M[N(SiMe₃)₂]_n, {M = Fe(II), Fe(III), Co(II), Ni(I), Cu(I)} or the reactions of lithium salts ArN(Li)-N(Ar)-PPh₂ with metal halides (GeCl₂, ZnCl₂, FeBr₂, CoCl₂, NiBr₂, CrCl₃, MnCl₂) are strongly dependent on nature of a metal and its ligand environment.Early transition metals or non-transition metals form stable phosphinohydrazides M[N(Ar)N(Ar)PPh₂]_n {M = Li, Zn, Ge(II), Mn(II), Cr(III), Fe(II)}.Starting ligand 2a and germylene Ge(NPhNPhPPh₂)₂ (7) were characterized by X-ray analysis.Germanium is coordinated additionally with a phosphorus atom of one of the diphenylphosphine groups.The distance Ge?P was found to be 2.563(1) Å.This coordination leads to an appreciable increase in a pyramidal geometry of nitrogen atoms relatively to a non-coordinated fragment.Late transition metals (Co, Ni, Cu) and metals with enhanced oxidation state (Fe³⁺) cause transformation of a phosphinohydrazide ligand.For Co(II), Ni(II), Fe(III) this leads quantitatively to aminoiminophosphoranates M(NAr-PPh₂NAr)_n.Complex Co[N(C₆H₄Bu^t)-PPh₂N-C₆H₄Bu^t]₂ (11) was characterized by X-ray analysis.Nickel(I) silylamide, (Ph₃P)₂NiN(SiMe₃)₂, being reacted with 2a yields azobenzene complex, (Ph₃P)₂Ni(PhNNPh), while copper(I) silylamide originally forms (PhNH-NPh-PPh₂)₂CuN(SiMe₃)₂ (18).Heating of the latter in toluene solution yields insoluble copper(I) diphenylphosphide, azobenzene, 2a and hexamethyldisilazane.The reaction of hydrazobenzene with Ph₂PCl (1:1) in methylene chloride for three days gives aminoiminophosphorane dihydrochloride[PhNH-PPh₂NPh] · 2HCl (3) in quantitative yield.     

Gas phase characterization by photoelectron spectroscopy of unhindered α-heterosubstituted germylenes

Two unhindered α-heterosubstituted (O and S) cyclic germylenes have been generated and characterized by the combination of flash vacuum thermolysis of stable germacyclopentenes and ultraviolet photoelectron spectroscopy. This coupling associated with ab initio calculations with the hybrid functional B3LYP and the 6-311G(d) basis set allows to predict the electronic properties of the generated germylenes. The thermodynamic stabilization of these reactive molecules by electronic delocalization of the heteroatom π lone pairs within the 4π orbitals of the germanium atom is clearly shown.     

Can N-heterocyclic germylenes behave as Lewis acids - is there another side to Meller germylenes?

N-Heterocyclic germylenes are known to exist in two structurally different forms, the planar Meller germylenes and the monoimino germylenes that feature an envelope structure. This essay reviews recent reports dealing with radical and cationic Meller type germylenes featuring the monoimino germylene structure, discusses their transformations and relationships, and asks the question whether indeed N-heterocyclic germylenes can be turned into Lewis acids.