Efficient Cobalt-Catalyzed Coupling of Amines and Siloxanes to Prepare Ceramics and Polymers

Abstract

The phosphine-substituted aryl diimine cobalt catalyst, ( Ph2PPr ADI)Co, has been found to mediate the dehydrocoupling of diamines or polyamines to poly(methylhydrosiloxane) (PMHS) to generate hydrogen and crosslinked solids in an atom-efficient fashion. The resulting siloxane diamine and siloxane polyamine networks persist in the presence of air or water at room temperature and can tolerate temperatures of up to 1600 °C. Upon lowering the catalyst loading to 0.01 mol %, ( Ph2PPr ADI)Co was found to catalyze the dehydrocoupling of 1,3-propanediamine and PMHS (m = 35) to generate a siloxane diamine foam with a turnover frequency of 157 s −1 relative to diamine consumption, the highest activity ever reported for Si−N dehydrocoupling. Furthermore, upon systematically reducing the number of potential branch points, the ( Ph2PPr ADI)Co-catalyzed dehydrocoupling of diamines with hydride-terminated poly(dimethylsiloxane) (PDMS) was found to yield linear siloxane diamine polymers with molecular weights of up to 47,300 g/mol.

Silane diamine copolymers: efficient synthesis, solvent absorption capacity, and limitations as coatings

“…Products 1a and 2a , which feature ethylenediamine linkers, were observed to hydrolyse considerably faster than the networks featuring longer chain diamines, which impart greater hydrophobicity. 19…”

“…18 Our group subsequently demonstrated that the aryl diimine (ADI) cobalt catalyst, ( Ph2PPr ADI)Co, can dehydrocouple diamines and hydrosiloxanes with turnover frequencies (TOFs) of up to 157 s −1 relative to substrate. 19 Prior to this study, the highest activity for Si-N dehydrocoupling was 91.7 s −1 , reported for the N-heterocyclic carbene complex, [Pt(I t Bu′)(I t Bu)][BAr F 4 ]. 13,20 In 2018, our group reported the synthesis of the manganese hydride dimer, [( 2,6-iPr2Ph BDI)Mn(µ-H)] 2 (1, Fig.…”

“…27 The observation of N-H and Si-H peaks indicates that the R and R′ substituents of 1a are often H. However, this product must also feature considerable crosslinking (i.e., where R = silane and R′ = amine) since a solid is obtained, rather than a linear oil. 19 The instability of silane diamine networks towards protic solvents and their insolubility in common organic solvents precluded bulk NMR and molecular weight analysis. 24 However, after soaking 1a in THF, MALDI-TOF MS analysis of the wash revealed Gaussian distributions ranging from 329 to 3079 g mol −1 .…”

“…Greater than 99% diamine conversion was observed for each trial in Tables 1 and 2, giving rise to substrate utilisation TOFs Table 2 Dehydrocoupling of diamines to OctSiH 3 using 0. of 66.7 h −1 and Si-N dehydrocoupling TOFs of at least 133 h −1 (since polymerisation requires the silylation of two or more N-H bonds per diamine). 19 To evaluate the maximum activity of the catalyst, the neat dehydrocoupling of ethylenediamine and phenylsilane was conducted in the presence of 0.01 mol% 1 and mesitylene as an internal standard. Aliquots were collected over the course of 3 h, the catalyst was deactivated by I 2 , and the percent conversion was determined by integrating the starting amine and internal standard 1 H NMR resonances.…”

“…Products 1a and 2a, which feature ethylenediamine linkers, were observed to hydrolyse considerably faster than the networks featuring longer chain diamines, which impart greater hydrophobicity. 19 Simultaneous thermal analysis was then performed to examine the thermal stability of each solid. In one set of experiments, samples of 1a-1f and 2a-2f were sealed within vials under N 2 , removed from the glovebox, and loaded onto a Mettler Toledo balance as quickly as possible to perform thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC) under N 2 (Table 3).…”