A Glimpse at the Chemistry of GeH₂in Solution. Direct Detection of an Intramolecular Germylene–Alkene π-Complex

Abstract

The photochemistry of 3-methyl-4-phenyl-1-germacyclopent-3-ene (4) and a deuterium-labeled derivative (4-d(2)) has been studied in solution by steady state and laser flash photolysis methods, with the goal of detecting the parent germylene (GeH(2)) directly and studying its reactivity in solution. Photolysis of 4 in C(6)D(12) containing acetic acid (AcOH) or methanol (MeOH) affords 2-methyl-3-phenyl-1,3-butadiene (6) and the O-H insertion products ROGeH(3) (R = Me or Ac) in yields of ca. 60% and 15-30%, respectively, along with numerous minor products which the deuterium-labeling studies suggest are mainly derived from hydrogermylation processes involving GeH(2) and diene 6. The reaction with AcOH also affords H(2) in ca. 20% yield, while HD is obtained from 4-d(2) under similar conditions. Photolysis of 4 in THF-d(8) containing AcOH affords AcOGeH(3) and 6 exclusively, indicating that the nucleophilic solvent assists the extrusion of GeH(2) from 4 and alters the mechanism of the trapping reaction with AcOH compared to that in cyclohexane. Laser flash photolysis of 4 in hexanes yields a promptly formed transient exhibiting λ(max) ≈ 460 nm, which decays on the microsecond time scale with the concomitant growth of a second, much longer-lived transient exhibiting λ(max) ≈ 390 nm. The spectrum and reactivity of the 460 nm species toward various germylene trapping agents are inconsistent with those expected for free GeH(2); rather, the transient is assigned to an intramolecular Ge(II)-alkene π-complex of one of the isomeric substituted hydridogermylenes derived from a solvent-cage reaction between GeH(2) and its diene (6) coproduct, formed by addition of HGe-H across one of the C=C bonds. These conclusions are supported by the results of DFT calculations of the thermochemistry associated with π-complexation of GeH(2) with 6 and the formation of the isomeric vinylgermiranes and 1,2-hydrogermylation products. A different species is observed upon laser photolysis of 4 in THF solution and is assigned to the GeH(2)-THF complex on the basis of its UV-vis spectrum and rate constants for its reaction with AcOH and AcOD.

Reversible Binding of Ethylene and Propylene by Germylenes

“…Herein, we report the first examples of reversible olefin binding by stable, two-coordinate germylenes, presumably via an intermediate π complex. 14 We demonstrate that Ge-(Ar Me6 ) 2 15 and Ge(Ar iPr4 ) 2 16 react reversibly with ethylene and that Ge(Ar iPr4 ) 2 also reversibly binds propylene at room temperature in toluene (Scheme 2, top). In addition we show that at elevated temperature Ge(Ar iPr4 ) 2 reacts with ethylene to yield the ethyl-substituted digermene {Ge(Et)(Ar iPr4 )} 2 with elimination of 1 equiv of Ar iPr4 H (Scheme 2, bottom).…”

“…Herein, we report the first examples of reversible olefin binding by stable, two-coordinate germylenes, presumably via an intermediate π complex . We demonstrate that Ge­(Ar Me6 ) 2 and Ge­(Ar i Pr4 ) 2 react reversibly with ethylene and that Ge­(Ar i Pr4 ) 2 also reversibly binds propylene at room temperature in toluene (Scheme , top).…”

Insight into the Decomposition Mechanism of Donor–Acceptor Complexes of EH2 (E = Ge and Sn) and Access to Germanium Thin Films from Solution

“…Does the first step involve LB-E or E-LA bond cleavage, or does a competing process, such as a 1,2-hydrogen shift from the tetrel element (E) to an N -heterocyclic carbene carbon center, occur en route to element deposition? Due to the transient nature of the EH 2 species, a combined experimental (kinetics) and computational approach was used to evaluate possible decomposition pathways available to ImMe 2 ·GeH 2 ·BH 3 . We also used computations to evaluate the decomposition energetics associated with the E­(II) dihydride adducts NHC·EH 2 ·BH 3 (NHC = IPr, ImMe 2 , or [(HCNH) 2 C:] (Im) and E = Ge or Sn).…”

Porous Ge@C materials via twin polymerization of germanium(ii) salicyl alcoholates for Li-ion batteries

“…[1][2][3][4][5] The early studies mainly focused on the use as ligands in transition metal complexes, 2,6-10 the reactivity in organogermanium chemistry 5,[11][12][13] and fundamental characterization. [14][15][16] While research on germylenes e.g., as model compounds in addition reactions such as of germanium into N-H and P-Cl bonds, progressed rapidly, [17][18][19][20][21][22][23][24][25][26][27] studies focusing on applications e.g., in catalysis 28 or as precursors for atomic layer deposition, 29 have rarely been reported until now. Quite recently molecular germanium(II) compounds were used to prepare germanium-based anode materials for Li-ion batteries, [30][31][32] motivated by the fact that germanium is a highly promising anode material considering its high gravimetric and volumetric theoretical capacities (1384 mA h g À1 /7367 A h L À1 for Li 15 Ge 4 ), high electrical conductivity and lithium-ion diffusivity.…”