Catalytic activity of N-heterocyclic carbenes in ring opening polymerization of cyclic siloxanes

N-Heterocyclic carbene-catalyzed dehydration of α,ω-disilanol oligomers

“…Recently we have also reported that NHCs are efficient catalysts for the ROP of cyclotetrasiloxane (D 4 ), which is one of the rare examples of the transformation of non-carbonyl compounds catalyzed by NHCs [8]. It is obvious that, in order to expand the scope of NHC applications, new types of catalytic activities should be developed.…”

Encapsulated N‐Heterocyclic Carbenes in Silicones without Reactivity Modification

“…In fact, a stable hypervalent NHC-SiR 4 complex D, using chlorosilanes with relatively strong Lewis acid character (SiR 4 = SiCl 4 , SiPh 2 Cl 2 ), has been reported. [11] Silicones containing NHCs were prepared by two methods: either by dissolving the NHC in already prepared PDMS (10 wt %) or through the polymerization of octamethylcyclotetrasiloxane (known as D 4 ) catalyzed by the NHC [12] itself in the presence of hexamethyldisiloxane (known as M 2 ) as a blocking agent.…”

“…Complete decomposition of 1 d occurs within only one week, which is probably due to the presence of bulky mesityl groups and the less basic character of 1 d (p-accepting groups on nitrogen atoms), which hamper the silicon-NHC interaction. [12] To better understand the interaction between NHCs 1 and silicones, we carried out some DFT and ab initio calculations [14,15] on the binding between NHC 1 e and model silicone oligomers with different substituents (4 a: R = Me, 4 b: R = Ph, Figure 1). The structures of the NHC-silicone complexes 5 a,b are shown in Figure 1.…”

“…In fact, in contrast to the relatively inert NHC complexes, [5,19] the reactivity of NHCs in silicones (1 a-PDMS, 1 c-MD 4 Ph M) was found to be almost identical to that of the free NHC 1. To check the reactivity of 1 a-PDMS as an organocatalyst, several known organic reactions catalyzed by NHCs, namely cyanosilylation, [20] transesterification (Scheme 1), [21] and the polymerization of D 4 [12] were tested. In all cases, reaction proceeded smoothly with the conditions previously described, and the resulting products were obtained in high yields.…”

N-heterocyclic carbenes as organocatalysts in controlled/living ring-opening polymerization ofO-carboxyanhydrides derived froml-lactic acid andl-mandelic acid

“…[19][20][21] NHCs have been applied in a wide range of monomers such as lactones, 20,22 cyclic carbonates, 23 epoxides, 24,25 and cyclic siloxanes. 26,27 The diverse structures and tunable catalytic performance of NHCs provide a far-ranging choice of catalyst in ROP, and these merits inspired us to investigate their application in OCAs. In this article, we first carried out a screening of NHCs by catalyzing the ROP of OCA of L-lactic acid (L-lacOCA; Scheme 2), and then synthesized a,x-dihydroxy telechelic, and star-shaped polymers with polylol initiators.…”