Synthesis of poly[1-(trimethylsilyl)-1-propyne] with extremely high molecular weight by using tantalum pentachloride-triphenylbismuth (1:1) catalyst

Abstract

Recently, not only the polymerization of acetylene but also that of substituted acetylenes has been intensively ~t u d i e d .~ We have succeeded in the synthesis of various substituted polyacetylenes.4 1-(Trimethylsily1)-1-propyne [CH3C=CSi(CH3),] polymerizes with the pentahalides of tantalum and niobium (TaC1, and NbC1,) alone 2b,5 to give a new polymer having weight-average molecular weights (i@$s) of 1 X 105-1 X 10,. Poly[l-(trimethylsily1)-1propyne] is white, soluble, air-stable, and electrically insulating, which gives a striking contrast to the properties of polyacetylene. Further, this polymer has proved to exhibit the highest oxygen permeability among all the existing polymer^.^,^ Organometallics of group 4 and 5 main-group metals (e.g., Ph4Sn, EhSiH, Ph3Bi) work as weak reducing agents and eventually play important roles as cocatalysts in the polymerization of substituted acetylenes by group 5 and 6 transition-metal catalysts. For instance, the polymerization of disubstituted acetylenes (e.g., 1-phenyl-1-propyne, 2-octyne, 1-chloro-2-phenylacetylene) by WCl, or MoCl, yields polymers only in the presence of these cocatalyst^.^ As another example, polymer degradation occurs in the polymerization of 1-phenyl-1-propyne by TaC1, and NbCl,, whereas it is restrained in the presence of the cocatalysts, resulting in the formation of high molecular weight poly-(1-phenyl-1-propyne) .7Here we report the synthesis of high molecular weight poly[l-(trimethylsily1)-1-propyne] with a catalyst system composed of a equimolar mixture of TaC1, and Ph3Bi [1:1 TaC1,-Ph3Bi]. In the course of our study on the cocatalyst effect, it was found that the TaC1,-Ph3Bi catalyst achieves extremely high MW, up to 4 x 10,. This molecular weight is the highest among those of the substituted polyacetylenes ever k n~w n .~~~ The influences of various cocatalysts and polymerization conditions are also discussed. Table I shows the effect of various cocatalysts on the polymerization of 1-(trimethylsily1)-1-propyne by TaC1, and NbC1,. Polymerizations were run in toluene at 80 "C for 24 h. TaC15 alone yielded quantitatively poly[l-(tri-methylsily1)-1-propyne] having a M, somewhat lower than 1 x lo6 [i@$s and number-average molecular weights ( &f ; s) were determined by gel permeation chromatography (GPC)]. It is of great interest that an equimolar mixture of TaC1, and Ph3Bi afforded the polymer with &fw as high as 4 X lo6 without reducing the polymer yield. Organoantimony, -tin, and -silicon cocatalysts also increased the 0024-9297/86/2219-2448$01.50/0 0 Table I Polymerization of 1-(Trimethylsily1)-1-propyne by Various TaC1,-and NbC1,-Based Catalysts" polymerb yield, % $fw X M, X catalvst Results and Discussion

Poly[1‐(trimethylgermyl)‐1‐propyne] and poly[1‐(trimethylsilyl)‐1‐propyne] with various geometries: Their synthesis and properties

“…For a number of catalytic systems, the use of cocatalysts significantly accelerates polymerization, the molecular mass of the resulting polymer grows, and the side reactions involving degradation of the produced polymer are suppressed. As for the mechanism of cocatalyst action in the polymerization of acetylenic monomers, it is known that they function as weak reducing agents of coordination catalysts and lead to the formation of active species engaged in rapid chain growth 29. No data are available on the effect of a cocatalyst on the geometrical structure of polyacetylene macromolecules.…”

(Arylimido)niobium(V)–Alkylidenes, Nb(CHSiMe3)(NAr)[OC(CF3)3](PMe3)2, That Enable to Proceed Living Metathesis Polymerization of Internal Alkynes

“…As described in the Introduction, niobium and tantalum catalyst systems [such as NbCl 5 or TaCl 5 –Ph 4 Sn or n Bu 4 Sn, Nb­(O-2,6-Me 2 C 6 H 3 ) n Cl 5– n (THF)– t BuMgCl or AlEt 3 ] − could polymerize disubstituted acetylenes, which are difficult by the other transition metal catalyst systems. − Reports for the metathesis polymerization of (unstrained) internal alkynes using complex catalysts have, however, been limited; ,− there are only two reports for 2-hexyne (and 2-butyne) polymerizations by the niobium– and tantalum–alkylidene catalysts at 25 °C. , As far as we know, this is the first clear demonstration of living polymerization of various internal alkynes and the living natures have been demonstrated at 50 °C (and even 80 °C by 4a ). Although we need further study to explore more possibilities of the catalyst development for the regio- and stereocontrols, the results presented here should be highly emphasized in terms of the polymer synthesis as well as the catalyst design in addition to better understanding in organometallic chemistry.…”

“…Niobium and tantalum catalyst systems [such as NbCl 5 or TaCl 5 –Ph 4 Sn or n Bu 4 Sn, Nb­(O-2,6-Me 2 ­C 6 H 3 ) n Cl 5– n (THF)– t BuMgCl or AlEt 3 ] − have been known to polymerize disubstituted acetylenes, − which are difficult by the other transition-metal catalyst systems. − Reports for the metathesis polymerization of (unstrained) internal alkynes using complex catalysts have, however, been limited. ,− We recently communicated that (imido)­niobium­(V)–alkylidene complexes containing the fluorinated alkoxo ligand, Nb­(CHSiMe 3 )­(NR′)­[OC­(CF 3 ) 3 ] (expressed as C and D , Chart ), act as the catalysts for (living) ring-opening metathesis polymerization (ROMP) of norbornene and the derivatives . In particular, it was suggested that 2-hexyne polymerization using Nb­(CHSiMe 3 )­(N-2,6-Me 2 C 6 H 3 )­[OC­(CF 3 ) 3 ]­(PMe 3 ) 2 would proceed in a living manner at 25 °C, whereas the polymerization using the vanadium­(V)–alkylidene, V­(CHSiMe 3 )­(N-2,6-Cl 2 C 6 H 3 )­(OC 6 F 5 )­(PMe 3 ) 2 , did not proceed under the same conditions, and the polymerization using the molybdenum–alkylidene, Mo­(CHCMe 2 Ph)­(N-2,6-Me 2 C 6 H 3 )­[OC­(CH 3 )­(CF 3 ) 3 ] (known as one of the most active catalysts), afforded polymers with bimodal molecular weight distributions .…”

Substituted polyacetylenes

“…77 The M w reached up to 4 Â 10 6 , which is one of the highest molecular weights of substituted polyacetylenes ever known. The intrinsic viscosity [g] of this polymer reached 13.2 dL g À1 .…”