Reversible and Irreversible Regioselective Alkyne Insertion into a Silyl-Substituted Stannylene

Area of Science:

• Organometallic Chemistry
• Silicon Chemistry
• Tin Chemistry

Background:

• Organotin compounds, specifically stannylenes, are reactive intermediates.
• The insertion of unsaturated molecules into metal-silicon bonds is a key transformation in synthetic chemistry.

Purpose of the Study:

• To investigate the regioselectivity and stereoselectivity of alkyne insertion into the Sn-Si bond of an electron-rich aryl(silyl)stannylene.
• To explore the reversibility of the insertion reaction and determine its thermodynamic parameters.
• To elucidate the mechanistic pathways and activation barriers using computational methods.

Main Methods:

• Synthesis of aryl(silyl)stannylene, Ar^MesSnSi(SiMe₃)₃.
• Reaction of the stannylene with various aryl- and alkyl- substituted alkynes.
• Characterization of vinyl-stannylene products using NMR spectroscopy.
• Variable temperature NMR spectroscopy to determine thermodynamic parameters.
• Quantum mechanical calculations to elucidate reaction mechanisms and activation barriers.

Main Results:

• Regioselective insertion of alkynes into the Sn-Si bond, yielding vinyl-stannylene products.
• Consistent syn arrangement of Sn and Si groups around the newly formed double bond.
• Exclusive incorporation of the sterically bulkier group at the 1-position (proximal to Sn) for unsymmetrical alkynes.
• Reversible insertion observed for 3-hexyne and trimethylsilylacetylene.
• Determination of thermodynamic parameters and activation barriers for the insertion and retro-insertion processes.

Conclusions:

• The aryl(silyl)stannylene serves as an effective substrate for regioselective and stereoselective alkyne insertion.
• The reaction outcome is governed by steric factors, favoring bulky groups at the tin-proximal position.
• The reversible nature of the insertion for specific alkynes opens possibilities for dynamic covalent chemistry applications.
• Computational studies provide insights into the reaction mechanism and transition states involved.