Time-resolved spectroscopic studies of the photochemistry of some diphenylgermylene (Ph₂Ge:) precursors

Abstract

The photochemistry of diphenylbis(trimethylsilyl)germane (2a) and 1,4-dihydro-5-methyl-1,2,3,4,9,9-hexaphenyl-1,4-germanonaphthalene (11) has been studied in solution by steady-state and laser flash photolysis methods with a view to detecting the transient germylene derivative diphenylgermylene (Ph2Ge), which has previously been shown to be the major product of photolysis of 2a and a closely related derivative of 11. Steady-state trapping experiments confirm the formation of Ph2Ge as the major germanium containing primary product in both cases; with 2a, the results indicate that other transient species are also formed in minor yields, including phenyl(trimethylsilyl)germylene (Ph(TMS)Ge, ca. 6%) and diphenyl(trimethylsilyl)germyl radicals (Ph2(TMS)Ge, ≥15%). Laser flash photolysis of 2a in deoxy genated hexane solution yields a complex mixture of overlapping transient absorptions, which is shown to be comprised of Ph2Ge, tetraphenyldigermene (15) and its oligomerization products, and another species with spectral characteristics similar to the Ph2(TMS)Ge radical. The latter has been independently generated by hydrogen abstraction from diphenyl(trimethylsilyl)germane by tert-butoxyl radicals. Compound 11 extrudes Ph2Ge more cleanly and efficiently upon photolysis in solution, yet laser flash photolysis affords excited triplet and triplet-derived species as the only detectable transient products; interpretation of the results for this compound is made difficult by its slow thermal decomposition to 5-methyl-1,2,3,4-tetraphenylnaphthalene. It is concluded that in spite of the fact that both 2a and 11 afford Ph2Ge in high yield upon photolysis, they are poor precursors for study of the species in solution by time-resolved UV–vis methods, owing to the formation of other, more strongly absorbing transient products than Ph2Ge, whose lowest energy absorption is characteristically weak.Key words: germylene, germyl radical, flash photolysis, disilylgermane, photochemistry.

Direct detection of methylphenylgermylene and 1,2-dimethyl-1,2-diphenyldigermene — Kinetic studies of their reactivities in solution

“…Such similarities are also evident in the UV-vis spectra of GeMe 2 and SiMe 2 (λ max = 453-465 nm (18,19)), as well as those of GePh 2 and SiPh 2 (λ max = 495 nm (18)). It thus seems clear that the transient absorptions assigned to GeMePh in the earlier time-resolved studies in solution, using 13 and 14 as precursors, must be due to other more strongly absorbing transient products; as we have shown previously for related systems (8), the likely candidates are conjugated germene derivatives and (or) germanium-centered radicals. For example, the conjugated germene derivative (15) that might be anticipated from photolysis of 13 can be predicted to exhibit an absorption maximum in the 430-450 nm range and exhibit moderate reactivity toward CCl 4 and DMB, based on analogies taken from related systems (7,8,20).…”

“…We have speculated that the problem is due to two main factors -the characteristic weakness of the lowest energy (S 0 → S 1 ) electronic transition in divalent group 14 compounds and the pronounced complexity of the photochemistry of the particular organo-germanium compounds (typically oligogermanes and oligosilagermanes) that have been employed as germylene precursors (7). As we have recently demonstrated (8), the combination of these factors can make transient germylenes relatively difficult to detect, even when they are the major products of photolysis.…”

A Minimal Toolset for Positional Diamond Mechanosynthesis

“…diphenylgermylene divalent radical ((C 6 H 5 2 -Ge:) 123 are being investigated both theoretically and experimentally in conventional chemistry. In Step 4 of RS36, the Ge• radical is hydrogenated to avoid pathological Ge C germene 124 125 bond formation (as observed experimentally in other molecules [126][127][128] ) after dehydrogenation of the CH 2 payload of the attached GM tool in a later Step.…”

Excited-State Photolytic Mechanism of Cyclopentene Containing a Group 14 Element: An MP2-CAS//CASSCF Study

“…Thanks to several laboratories, nowadays many substituted germylenes have been detected, and their reactivities have been studied using laser flash photolysis techniques. − See Scheme (and Scheme A in Supporting Information). − From these available photochemical results, it is apparent that the bulkiness of substituents on either the Ge atom or C atoms of unsaturated germacyclopentenes is an important factor in controlling not only the reaction routes but also the stereochemistry of the final photoproducts (1,3-butadienes).…”