Flash vacuum thermolysis of 3,4‐dimethyl‐1‐germacyclopent‐3‐enes: UV photoelectron spectroscopic characterization of GeH₂ and GeMe₂

Abstract

Gas-phase UV photoelectron spectra of germylene (GeH 2 ) and its dimethyl analogue (GeMe 2 ) have been recorded, using flash vacuum thermolysis of 3,4-dimethyl-and 1,1,3,4-tetramethylgermacyclopent-3-ene to generate these reactive species in the inlet of the photoelectron spectrometer. The lowest vertical ionization bands for GeH 2 (9.4 eV) and GeMe 2 (8.2 and 10.0 eV) have been located with the aid of time-dependent density functional theory calculations carried out at the B3LYP/6-311G(d,p) level of theory. Similar experiments carried out with 3,4-dimethyl-1,1-diphenylgermacyclopent-3-ene, in an attempt to record the photoelectron spectrum of diphenylgermylene (GePh 2 ), were less conclusive, but are consistent with the theoretically predicted lowest lonization potential of 8.0-8.2 eV for GePh 2 . Photoelectron spectra of the three germacyclopentene derivatives are also reported.

Gas-phase synthesis and characterization of heteroleptic divalent germanium compounds by FVT/UV-PES

“…This sensitivity to substitution at germanium has been noted as well in the 3,4-dimethyl-1-germacyclopent-3-ene derivatives that have been studied previously [23]. Finally, there exists a global lowering of the entire set of IEs throughout the series 4a > 6a > 5a.…”

“…For the series of germacyclopentenes 4a-6a, the calculated IEs obtained with the OVGF and ''correction" methods are thus in good general agreement with the experimental spectra. Less satisfactory correlations are obtained from the TD-DFT method, as was also found previously for hydrido-, methyl-and phenyl-substituted 3,4-dimethyl-1-germacyclopent-3-ene derivatives [23]. Since the calculated IEs associated with the lower-lying orbitals in the TD- Table 1 Calculated (B3LYP/6-311G (d,p)) geometrical parameters (distances in Å, bond angles in°) of 4a, 5a and 6a.…”

“…Ionization energies for 4a, 5a and 6a were calculated by three methods: TD-DFT, OVGF, and empirical correction of the calculated Kohn-Sham energies, as employed in our previous studies of GeH 2 , GeMe 2 , GePh 2 , and the germacyclopentene derivatives from which they were generated [23]. The calculated IEs and corresponding MO-assignments for the three compounds are listed in Tables 2-4.…”

“…Solvents and intermediate compounds were distilled prior to use. GeCl 2 -dioxane [30], and 1,1-dichloro-3,4-dimethylgermacyclopent-3-ene [23] were prepared according to the previously reported methods. 1 H NMR spectra were recorded at 400 MHz on a Bruker AMX 400 spectrometer, while 13 C NMR spectra were recorded at 125 MHz on a Bruker AM Avance DRX500 spectrometer; chemical shifts are reported in ppm (d) relative to tetramethylsilane.…”

“…As in our previous studies, flash vacuum thermolysis techniques have been employed for the generation of these shortlived species under conditions where their UV photoelectron spectra can be measured, and the spectra have been analysed with the aid of time dependent density functional theory (B3LYP/6-311G (d,p)) and outer valence green's function (6-311G(d,p)) calculations. As we have discussed previously [22], and shown specifically in previous studies of transient germylenes by PES [12,20,23], these methods offer a quite reasonable compromise between the quality of the results and the cost associated with calculations of this type. The course of the thermolysis reactions has also been verified by mass spectrometric methods and the results of chemical trapping experiments.…”