Matrix Isolation of Germacyclopentadienes:  Direct Spectroscopic Evidence for Germylene-to-Germene Photochemical Interconversion

UV irradiation of matrix-isolated 1,1-diazido-1-germacyclopent-3-ene (4b) produced 1H-germole (1-germacyclopenta-2,4-diene; 1b) and 1-germacyclopent-3-ene-1,1-diyl (2b) as major products along with 3H-germole (1-germacyclopenta-1,4-diene; 5b) and 2H-germole (1-germacyclopenta-1,3-diene; 6b) as minor products. During irradiation at selected wavelengths a photoconversion of 1b into 5b and reversible interconversion of 2b and 6b have been observed and provide experimental evidence for a germylene-to-germene rearrangement. Similar experiments were carried out on deuterated analogues, and the precursor 4b-d6 produced 1b-d6, 2b-d6, 5b-d6, and 6b-d6. Full vibrational assignment in the IR spectra of 1b, 2b, 5b, and 6b has been proposed on the basis of restricted Hartree−Fock (DZ+d) calculations for those molecules and their d6 analogues and literature data on the silicon analogues 1a, 2a, 5a, 6a, and other related molecules. The UV−vis spectra are interpreted by comparison with the experimental and computed trans...