Reversible Coupling of Germylone with Isocyanates.

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry

Background:

• N-heterocyclic carbenes (NHCs) are versatile ligands in organometallic chemistry.
• Germylenes, compounds featuring a divalent germanium atom, exhibit unique reactivity.
• The synthesis and characterization of novel germanium-based compounds are of significant interest.

Purpose of the Study:

• To investigate the reactivity of germylone dimNHCGe with isocyanates.
• To synthesize and characterize novel alkyl carboxamido germylenes.
• To explore the reversibility of C-C bond formation in reduced germanium compounds.

Main Methods:

• [2+2] cycloaddition reactions between germylone dimNHCGe and various isocyanates.
• Synthesis and isolation of novel germylene products.
• Isocyanate metathesis reactions at elevated temperatures.
• Density Functional Theory (DFT) calculations to elucidate reaction mechanisms.

Main Results:

• Germylone dimNHCGe successfully undergoes [2+2] cycloaddition with isocyanates (RNCO) to yield alkyl carboxamido germylenes.
• Novel germylenes 7 and 8 were synthesized, featuring a crucial C-C bond between the carbene carbon and the isocyanate moiety.
• Isocyanate metathesis was observed upon heating germylene 8 with 4-tolyl isocyanate, indicating reversible C-C bond formation.
• DFT calculations supported a mechanism involving reductive dissociation of isocyanate for the observed reversibility.

Conclusions:

• The study demonstrates a novel [2+2] cycloaddition pathway for germylones with isocyanates, leading to C-C bond formation.
• The reversible nature of this C-C bond formation on a reduced germanium center was established.
• This work expands the known reactivity of germylenes and offers insights into dynamic C-C bond formation in main group chemistry.