Chlorine-free germanium processing

Chlorine-free germanium processing are methods of germanium activation to form useful germanium precursors in a more energy efficient and environmentally friendly way compared to traditional synthetic routes. Germanium tetrachloride is a valuable intermediate for the synthesis of many germanium complexes. Normal synthesis of it involves an energy-intensive dehydration of germanium oxide,

GeO

2

{\displaystyle {\ce {GeO2}}}

, with hydrogen chloride,

HCl

{\displaystyle {\ce {HCl}}}

Due to the environmental and safety impact of non-recyclable, high energy reactions with

HCl

{\displaystyle {\ce {HCl}}}

, an alternative synthesis of a shelf-stable germanium intermediate precursor without chlorine is of interest. In 2017, a synthesis of organogermanes,

GeR

4

{\displaystyle {\ce {GeR4}}}

without using chloride species was reported, allowing for a much more environmentally friendly and low energy synthesis using

GeO

2

{\displaystyle {\ce {GeO2}}}

,

Ge

(

0

)

{\displaystyle {\ce {Ge(0)}}}

, and even selectively activating germanium in the presence of zinc oxide (

ZnO

{\displaystyle {\ce {ZnO}}}

), resulting in products that are bench stable and solid.

Synthesis of organogermanes

Oxidation of germanium metal

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. Referring to the scheme below, when

Ge

(

0

)

{\displaystyle {\ce {Ge(0)}}}

, 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

Ge

(

0

)

{\displaystyle {\ce {Ge(0)}}}

oxidized to

Ge

(

IV

)

{\displaystyle {\ce {Ge(IV)}}}

. This reaction was shown to work both at the milligram and the gram scale, proving its efficiency in the bulk scale.

Dehydration of GeO2

Following a nearly identical reaction scheme as the oxidation of germanium metal with ortho-quinone, dehydration of

GeO

2

{\displaystyle {\ce {GeO2}}}

with catechol ligands results in the same product as the oxidation product, with similar yield 74% on milligram scale and 84% on the gram scale.