VACUUM PYROLYSIS MATRIX-ISOLATION FTIR AND DENSITY-FUNCTIONAL THEORETICAL-STUDIES OF TRANSIENT DIMETHYLGERMANONE, (CH3)(2)GE=O

The transient organic germanone (CH3)(2)Ge=O (1) was generated by vacu um 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 octameth ylcyclotetragermoxane (4), and directly observed in argon cryogenic so lid matrixes at 12 K by FTIR spectroscopy. The unstable dimer of 1-tet ramethyl-1,3-cyclodigermoxane (6)-has been tentatively identified in t he spectra of matrix-isolated pyrolysis products from 2-4. The product ion of the transient germene (CH3)(2)-Ge=CH2 (9) and acrolein from 2 a nd of isopropenyl methyl ketone from 3 have also been observed, provid ing 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 th e density functional theory B3LYP/6-311G(d,p) calculated harmonic freq uencies and infrared intensities, assisted by vibration visualization and calculations of potential energy distributions (PED) for each norm al mode. The excellent agreement between the experimental and calculat ed frequencies and the observation of isotopic splittings of the Ge=O and Ge-C stretching fundamentals due to natural abundances of germaniu m, being in accord with the computed isotopic shifts, provide firm evi dence for the structural identification of germanone 1. The observed f requency and the calculated force constant and bond order of the Ge=O moiety in 1 are found to be lower than those in the parent germanone H 2Ge=O (5) and in F2Ge=O. These studies correct the assignment of the G e=O stretching frequency in 1 given earlier in our preliminary report.