Polymerization of Substituted Acetylenes by the Grubbs–Hoveyda Ru Carbene Complex

Abstract

ABSTRACT:Polymerization of various mono-and disubstituted acetylenes was investigated by using GrubbsHoveyda catalyst (1). Hexyl propiolate (2) and 1-phenyl-2-(p-trimethylsilyl)phenylacetylene (3) Substituted polyacetylenes have been gathering much attention due to their potential applications to material-separation membranes, and optoelectronic and related fields.1 These polymers have been obtained by polymerization of corresponding acetylenic monomers in the presence of transition metal catalysts. Catalysts including group 5 and 6 transition metal and Rh have traditionally been employed to induce their polymerization. Among them, halides of early transition metals such as TaCl 5 , NbCl 5 , MoCl 5 , and WCl 6 in conjunction with organometallic cocatalysts polymerize various mono-and disubstituted acetylenes to give high molecular weight polymers in good yield. Some well-defined Ta, Mo, and W carbenes, so-called Schrock carbenes, induce living polymerization of substituted acetylenes. [2][3][4][5] This implies that the group 5 and 6 transition metal-catalyzed polymerization proceeds by the metathesis mechanism. One of the drawbacks of the early transition metal is that they are readily deactivated by polar groups in the monomer and polymerization solvents because of their high oxophilicity.Another type of catalysts frequently used for the polymerization of substituted acetylenes are rhodium (Rh) catalysts. Rh catalysts can polymerize only monosubstituted acetylenes such as phenylacetylene and its ring-substituted derivatives, 6-11 N-propargylamides, 12-17 and propiolic esters. [19][20][21][22][23] The Rh-catalyzed polymerization proceeds by the insertion mechanism, and features excellent tolerance to polar subsituents in the monomer 24,25 and protic solvents. 26 The Rh-based polymers generally possess high cis stereoregularity, which is indispensable for the formation of helical structures of poly(N-propargylamide)s. 12-17A huge number of studies on the synthesis and catalysis of ruthenium (Ru) carbene complexes have been reported in these several years. Ru carbene complexes represented by Grubbs' first-and secondgeneration catalysts exhibit high activity in olefin metathesis reactions such as ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM), cross metathesis (CM). 27 Compared to early transition metal-based metathesis catalysts, Ru carbene complexes display tolerance against protic functional groups in these metathesis reactions as well as considerable stability to oxygen and moisture. It should also be noted that many Ru complexes have well-defined carbene structures, which enables to directly generate carbene-type active species without adding cocatalysts. The Grubbs' second-generation complex reportedly reacts with diphenylacetylene stoichiometrically to afford 3 -vinylcarbene complex, which is regarded as an intermediate of the polymerization of acetylenes.28 Ru-catalyzed polymerizations of acetylene 29 and diyne compounds 30,31 have recently been reported. Though an Ru carbene ...

Substituted polyacetylenes

“…Fortunately, we were able to do pioneering works and obtain many interesting results in this new area. We are now engaged in challenging subjects that include novel catalysts (e.g., Ru carbenes, 113 highly active Rh-based living polymerization catalyst), construction of new polymer architectures derived from substituted acetylenes (e.g., polymer brushes, 114 dendronbearing polyacetylenes), preparation of highly efficient CO 2 separation membranes based on substituted polyacetylenes, 115 and development of novel functional polymer materials (e.g., organic battery materials). 116 Only about 80 years have passed since the mankind began to synthesize artificial polymers, whereas organisms have spent about four trillion years to develop elaborately designed, highly functional biomacromolecules such as DNA, proteins, and polysaccharides.…”

Polymerization of Diphenylacetylenes with Polar Functional Groups by the Grubbs–Hoveyda Ru Carbene Catalyst

“…Ethyl p-iodobenzoate (TCI), ethyl m-iodobenzoate (TCI), heptylamine (TCI), p-iodoaniline (Aldrich), m-iodoaniline (Aldrich), octanoic acid (Aldrich), N-methylmorpholine (Wako), isobutyl chloroformate (Wako), N-t-BOC-iodoaniline (t-BOC ¼ tert-butoxycarbonyl, Wako), phenylacetylene (Aldrich), triphenylphosphine (Wako), copper(I) iodide (Wako), triethylamine (Wako) were used as received. 1-Phenyl-2-(4-trimethylsilyl)phenylacetylene (3), [7] 1-(4-tertbutyldimethylsiloxy)phenyl-2-phenylacetylene (4), [6c] and 1-(4-tert-butyldimethylsiloxy)phenyl-2-(4-fluorophenyl)acetylene (5) [6a] were prepared according to the literature methods. Monomers 6-11 were synthesized as shown in Scheme 1 according to the methods reported in the literature.…”

“…The Ru-based poly(2) was a white polymer, while the Ta-based poly(2) is yellow, similar to the case of previously examined polymer of 1-phenyl-2-(trimethylsilylphenyl)acetylene (3). [5] In the polymerization of monomers 4 and 5 with the Ta catalyst, poly(5) bearing fluorine atoms has higher molecular weight (M w > 6.0 Â 10 6 ) than those of poly(4) (M w ¼ 4.0 Â 10 6 ) without fluorine atoms. [6a,6b] The same tendency was observed in the present case, i.e., the number-average molecular weights (M n ) of poly(4) and poly (5) were 93 000 and 178 000, respectively (runs 3 and 4).…”

“…[5] However, polymerization of disubstituted acetylenes containing polar functional groups was not examined.…”

“…It has been revealed that the geometric structure of the poly(3) obtained with the Ru catalyst (1) was different from that formed with the Ta catalyst. [5] The different geometrical structures of the polymer may affect its gas permeation properties. This paper reports on the polymerization of diphenylacetylene derivatives bearing relatively nonpolar (4, 5) and polar (6-11) functional groups using Grubbs-Hoveyda catalyst (1), and copolymerization of the ester groupcontaining monomers (6 and 7) with 3 (see Figure 1).…”