Regio- and stereospecific cyclopolymerization of 1,6-heptadiynes and 1,5-hexadiynes

Abstract

The synthesis of poly(ene)s exclusively based on one single repetitive unit, i.e., 1,2cyclopent-2-enylenvinylenes,is described. Polymers containing >96% 1,2-cyclopent-2-enylenvi nylene units were obtained by low-temperature-initiated cyclopolymerization of diethyl dipropargylmalonate (DEDPM) by Mo(N-2,6-i-Pr 2-C 6 H 3)(CHCMe 2 Ph)(OCH(CH 3 / 2 / 2. In the presence of quinuclidine, >96% 5-membered ring structures were realized at room temperature, e.g., using Mo(N-2,6-Me 2-C 6 H 3)(CHCMe 2 Ph)(OC(CH 3 / 3 / 2. 4-(Ethoxycarbonyl)-4-(1S, 2R,5S)-(C)-menthyl-1,6-heptadiyne was cyclopolymerized to determine the con guration of the double bond (i.e., the cis/ trans ratio) and the tacticity of the poly(ene) backbone. Poly(4-(ethoxycarbonyl)-4-(1S,2R,5S)-(C)-menthyl-1,6heptadiyne) again consisted of >96% 5-membered rings and possessed an all-trans tactic, presumably isotactic structure. A linear plot of number of monomers added (N) vs. molecular weight suggested that cyclopolymerization of DEDPM proceeded in a living manner. At least a class-V living system was con rmed by the stepwise synthesis of poly(DEDPM). Molecular weight distributions (PDIs) of 1.16-1.37 resulted from ratios of the rate constants for polymerization (k p) to initiation (k i), k p =k i À 1. In uences of temperature, the base and steric and electronic effects of the arylimido and alkoxy ligand are presented. Complementary to the use of well-de ned Schrock initiators, poly(DEDPM) containing exclusively 5-membered rings was accessible by the use of the quaternary systems MoCl 5-n-Bu 4 Sn-EtOH-quinuclidineand MoOCl 4-n-Bu 4 Sn-EtOH-quinuclidine. Though virtually identical polymers were obtained, the polymerization systems themselves were controlled, yet not living, as is the case with Schrock initiators. Selected polymer properties such as stability, degradation behavior, conductivity, and thermoresponsive behavior will be discussed. Finally, the polymerization behavior of other monomers such as N,N-dipropargylaniline (1), dipropargyl sul de (2), 1,8-diethynylnaphthalene (3) and 1,2-diethynyltetramethyldisilane (4) is presented.

Multiple Metal–Carbon Bonds for Catalytic Metathesis Reactions (Nobel Lecture)

“…Although work is still ongoing in this area, it now appears possible to do so. [62,63] In 1992 Fu and Grubbs published two papers in which they demonstrated how [Mo(NAr)(CHCMe 2 Ph){OCMe-(CF 3 ) 2 } 2 ] could be employed to make cyclic olefins quickly and efficiently that contain functionalities other than a C = C bond, [64,65] with the only other product being a volatile olefin such as ethylene, propylene, or butene (Scheme 4). Rings of many sizes, and even rings that contain tetrasubstituted olefinic bonds, could be prepared.…”

Stereoselective Cyclopolymerization of Polar 1,6‐Heptadiynes by Novel, Tailor‐Made Ruthenium‐Based Metathesis Catalysts

“…[25,26] In order to be able to assign the corresponding chemical shifts to a particular ring size, the chemical shifts of the corresponding model compounds ( Figure 3) with structures similar to the corresponding repetitive units were determined. [8,9,[11][12][13]28,29] A comparison of these data revealed that the chemical shift of the carbonyl carbon of the ester group (d ¼ 175 4 ppm) in poly-M2 was close to those in both model compounds (d ¼ 176.1 and 175.9 ppm, respectively). The same applied to the tertiary carbon in the polymer (d ¼ 39.9 versus 39.9 and 41.5 ppm in the corresponding model compounds).…”

Cyclopolymerization of N,N- Dipropargyl-3,4-dialkoxyanilines Using Schrock and Grubbs-Hoveyda Initiators: Influence of Initiator Structure on the Mode of Insertion

“…Generally, the cyclopolymerization of 1,6‐heptadiynes can proceed via α ‐ or β ‐insertion, resulting in the formation of conjugated, polyacetylene‐type polymers based on either five‐ or six‐membered repeat units (Scheme ) 1, 2. Depending on the monomer structure, different Mo‐based Schrock initiators allow for the synthesis of cyclopolymerization‐derived polyenes either based on five‐14, 15, 17–19 or six‐membered repeat units6, 7 or a mixture thereof 1, 2. With the modified Grubbs‐Hoveyda initiators developed in our group, an alternative catalytic system has been established that is capable of polymerizing 1,6‐heptadiynes and N,N‐ dialkyl‐ N,N‐ dipropargylammonium compounds via a regioselective α ‐insertion 20–22, 24, 28, 29.…”

“…However, in terms of material's properties, particularly N‐containing cyclopolymerization‐derived polymers are of significant interest, since they may easily be protonated or subjected to oxidation, offering access to (semi‐) conducting, e.g., polypyrrole‐type polymers. While our very first attempts to realize soluble polymers of N,N‐ dipropargylaniline failed,19 we now report on the successful accomplishment of this task. Here, we particularly focus on the influence of the initiator's structure on the mode of insertion and, in due consequence, on the structure of the repeat unit of the resulting polymer.…”

“…Substituents at the 4‐position provide good solubility of the polymers in common organic solvents (e.g., toluene, CH 2 Cl 2 , CHCl 3 ) 1, 3, 6, 7. While the regioselective cyclopolymerization of 1,6‐heptadiynes such as diethyl dipropargyl malonate and related monomers has been described by Schrock and co‐workers and Buchmeiser and co‐workers,7–25 the factors that govern the regioselectivity in the cyclopolymerization of 4‐azaheptadiynes and related compounds has been addressed only recently 26. Thus, the polymerization of N,N‐ dialkyl‐ N,N‐ dipropargylammonium salts can be accomplished with the aid of various Grubbs‐Hoveyda type initiators bearing electron‐withdrawing ligands such as trifluoroacetates (CF 3 COO – ) 20–22.…”