From CO₂ to Polysiloxanes: Di(carbamoyloxy)silanes Me₂Si[(OCO)NRR′]₂ as Precursors for PDMS

Abstract

Double insertion of carbon dioxide into the Si−N bonds of diaminosilanes of the type Me 2 Si(NRR′) 2 gives di(carbamoyloxy)silanes Me 2 Si[(OCO)NRR′] 2 . The reactions proceed exothermically and quantitatively in most cases. A comprehensive analysis of the CO 2insertion products including single-crystal X-ray structure analyses was carried out. Quantum chemical calculations indicate an activation energy of about 124 kJ/mol for both the first and the second insertion and support the exothermal nature of the reaction. Investigation of the thermal decomposition of the di(carbamoyloxy)silanes Me 2 Si[(OCO)NRR′] 2 reveals the formation of oligo-and polysiloxanes.Depending on the thermolysis parameters, isocyanates, amines, and/or ureas are formed in addition to the siloxanes. Various methods were applied to study the decomposition process and to identify and quantify the products, including thermal analyses, mass spectrometry, and FTIR and NMR (solution and solid-state) spectroscopy. The overall reaction scheme provides a novel route to polysiloxanes which uses carbon dioxide as an oxygen source.

Lactamomethylsilanes – Synthesis, Structures, and Reactivity towards CO2 and Phenylisocyanate

“…Many aminosilanes were synthesized via this route in nonpolar solvents like n ‐hexane or n ‐pentane , . The used lactams as well as the synthesized lactamomethylsilanes are not soluble in these solvents.…”

“…The Si–N bond is prone towards hydrolysis and alkoholysis. Additionally, some substances containing Si–N bonds react with heteroallenes like CO 2 and isocyanates via insertion reactions yielding useful products such as ureas, carbamates, and polysiloxanes, among others . Therefore, in the presented study we have synthesized lactamomethylsilanes of the type Me x SiLac (4– x ) ( x = 0, 1, 2, and 3) [Lac = γ‐butyrolactam, δ‐valerolactam, ε‐caprolactam, and 1‐isoindolinone (phthalimidine)] in order to investigate their structures and reactivities.…”

Formation of Aromatic O‐Silylcarbamates from Aminosilanes and Their Subsequent Thermal Decomposition with Formation of Isocyanates

“…In the context of the more and more evolving topic of carbon dioxide utilization for the production of various crucial chemicals, we aim at employing CO 2 as an oxygen source as well as a carbon source in the synthesis of compounds such as (poly) siloxanes, urea derivatives and isocyanates. [1][2][3][4]5,6,7] One key step is the insertion reaction of CO 2 into SiÀ NR 1 R 2 bonds of aminosilanes with formation of the desired R 1 R 2 NC(O)OSi motif (cf. carbamoyloxysilane, carbamatosilane, O-silylcarbamate; Si = tetravalent silicon with three further substituents), as shown in Scheme 1.…”

“…carbamoyloxysilane, carbamatosilane, O-silylcarbamate; Si = tetravalent silicon with three further substituents), as shown in Scheme 1. These compounds may serve as precursors for isocyanates, formation of which depends on cleavage of the Osilylcarbamate motif with release of a suitable leaving group R 1 OSi. In this context, we refer to "aminosilanes" in a narrow sense as those compounds containing Si-bound amine groups, i. e., SiÀ N bonds (cf.…”

Crystalline Aminoorganosilanes – Syntheses, Structures, Spectroscopic Properties

“…Another reaction is the insertion of CO 2 into the SiN bond of aminosilanes yielding carbomoyloxysilanes of the type Me 2 Si[(OCO)NR 2 ] 2 15,16. It might be possible to gain further insight into the mechanism of CO 2 insertion by using solid aminosilanes.…”