Chlorine-free germanium processing
Normal synthesis of it involves an energy-intensive dehydration of germanium oxide,
[1] Due to the environmental and safety impact of non-recyclable, high energy reactions with
, an alternative synthesis of a shelf-stable germanium intermediate precursor without chlorine is of interest.
without using chloride species was reported, allowing for a much more environmentally friendly and low energy synthesis using
[2] Glavinović et al. have synthesized organogermanes using ortho-quinone, which is both redox "non-innocent" and acts as a pseudo-halide, resulting in an air and moisture stable beige solid.
, ortho-quinone, and pyridine (acting as an auxiliary ligand) were milled via liquid assisted grinding in a 1:1 mixture of toluene and water, the resulting organogermane was recrystallized in toluene resulting in 88% yield.
In this reaction, the quinone ligands each undergo a two-electron oxidation, resulting in the
[citation needed] Following a nearly identical reaction scheme as the oxidation of germanium metal with ortho-quinone, dehydration of
These reactions could provide an alternative to normal oxide separations for other metals that are energy intensive and otherwise wasteful.
The zinc byproduct can be distilled at high temperatures, leaving only germanium tetrachloride.
The unreacted zinc oxide can be washed away with dichloromethane and the bis(catecholate) germanium product recrystallized in cyclohexane.
Despite zinc oxide being present in the reaction vessel, the intermediate germanium product yields remain high, being 64 and 66%.
[7] The mechanochemical activation of germanium described above can be used with a variety of auxiliary amine-based ligands and not just pyridine as used in the syntheses above.
Uni-dentate ligands such as N-methyl imidazole can be used to create a trans-disposed octahedral germanium product, isostructural to the complexes of both the catechol and ortho-quinone that contain pyridine.
For example, in a reaction using tetramethylethylenediamine as a chelating bi-dentate diamine affords the cis- product with catechol ligands at the other octahedral binding sites.
More research as additionally been done to show that the nitrogen-containing ligands can be biologically active ones which operate at very low reduction potentials.
[8] The intermediates prepared by the above method are able to easily undergo substitution reactions with nucleophiles to form tetraorganogermanes,
Germane is a key material in optical and electronic device fabrication.
[9] These substitution reactions return the original catechol ligand, making this germanium activation process easily recyclable.
A solution of 20 equivalents of an alkyl or aryl Grignard reagent in tetrahydrofuran, combined with bis(catecholate) complex leads to a homogeneous solution of reagents in THF.
Referring to the scheme below, treating intermediate 2 with an additional equivalent of Grignard reagent yields 3 at a faster rate than the rate to make 2, and treatment of 3 with two equivalents of reagent yields 4 at even more quickly.
, in which the germanium center becomes more sterically hindered over the course of the reaction as ligand exchange of the carbons and the chlorides progresses, making the substitution more difficult.
[citation needed] The stereochemical selectivity of the substitution reaction is further enforced by the identity of the auxiliary amine ligand.
By using a more sterically encumbered amine ligand such as triethylamine, a 1.67:1 mixture of dibutyl-germane-η2-catecholate and tributylgermyl-η1-catecholate is produced after substitution with two equivalents of
This proves the effect of steric encumbrance on the product of the substitution reaction as the resulting tri-substituted product has the least sterically encumbered oxygen remaining bonded to the catecholate.
, is extremely important in the field of optoelectronics and is a good candidate for vapor deposition to form thin films of germanium.
) in dibutyl ether with argon as a carrier gas, the substitution reaction yields high purity germane in the Ar carrier gas with no evolution of volitile Ge byproducts.
This reaction pathway for production of germane requires no postsynthetic processing or purification, proving this to be more advantageous than current methods.
