Vacuum Pyrolysis−Matrix Isolation FTIR and Density Functional Theoretical Studies of Transient Dimethylgermanone, (CH3)2GeO

Abstract

The transient organic germanone (CH3)2GeO (1) was generated by vacuum pyrolysis from three precursors, 3,3-dimethyl-6-oxa-3-germabicyclo[3.1.0]hexane (2) and its 1,3,3,5-tetramethyl analogue (3) and octamethylcyclotetragermoxane (4), and directly observed in argon cryogenic solid matrixes at 12 K by FTIR spectroscopy. The unstable dimer of 1tetramethyl-1,3-cyclodigermoxane (6)has been tentatively identified in the spectra of matrix-isolated pyrolysis products from 2−4. The production of the transient germene (CH3)2GeCH2 (9) and acrolein from 2 and of isopropenyl methyl ketone from 3 have also been observed, providing evidence for a new route of the thermal decomposition of epoxides 2 and 3. Vibrational assignments of the spectral bands, attributed to germanone 1 and its cyclodimer 6, have been done by comparison with the density functional theory B3LYP/6-311G(d,p) calculated harmonic frequencies and infrared intensities, assisted by vibration visualization and calculations of potential energy distributions (PED) for each normal mode. The excellent agreement between the experimental and calculated frequencies and the observation of isotopic splittings of the GeO and Ge−C stretching fundamentals due to natural abundances of germanium, being in accord with the computed isotopic shifts, provide firm evidence for the structural identification of germanone 1. The observed frequency and the calculated force constant and bond order of the GeO moiety in 1 are found to be lower than those in the parent germanone H2GeO (5) and in F2GeO. These studies correct the assignment of the GeO stretching frequency in 1 given earlier in our preliminary report.