Controlled and Living Polymerizations Induced with Rhodium Catalysts. A Review

Abstract

In the last fifteen years, a large variety of specialty polymers of diverse chemical structure and functionality have been synthesized with the rhodium-based catalysts. The high tolerance to the reaction medium and functional groups of monomers, as well as ability to control various structure features of the polymer formed are typical properties of these catalysts. In addition, some rhodium catalysts can be anchored to inorganic or organic supports or dissolved in ionic liquids to form heterophase polymerization systems, which opens the way to pure, well-defined polymers free of the catalyst residues, as well as to recycling rhodium catalysts. This review provides a survey on the polymerization reactions induced with rhodium-based catalysts, in which one or more structure attributes of the polymer formed are subject to control. The structure attributes considered are (i) sequential arrangement of monomeric units along polymer chains; (ii) head-tail isomerism of polymer molecules; (iii) configurational structure of polymer molecules; (iv) conformation of polymer molecules; and (v) molecular weight and molecular-weight distribution of the polymer formed. A review with 188 references.

Substituted polyacetylenes

“…A pioneering work was done by Kern as early as the 1960s, 57 in which monomer 1 was polymerized with RhCl 3 -LiBH 4 and (Ph 3 P) 3 RhCl. The selective formation of cis-transoidal structure was confirmed by Furlani and Feast using 1 H and 13 C NMR, 58 and it was found by Tabata that Et 3 N works as an effective cocatalyst in the [(nbd)RhCl] 2 -catalyzed (nbd: 2,5-norbornadiene) polymerization. 59 The features of Rh catalysts as compared with group 5 and 6 metathesis catalysts include cis-transoidal structure of the formed polymer, tolerance to polar moieties in the monomer and to polar solvents, and restriction of the kinds of monomers to monosubstituted acetylenes.…”

“…However, there was no convincing evidence at that time. In 1980 Katz reported that Fischer and Casey carbenes polymerize substituted acetylenes, 42 and further he analyzed the partly deuterated poly(1) by using 13 C NMR nutation technique to conclude that the Mo-catalyzed polymerization proceeds by the metathesis mechanism. 43 If the polymerization of substituted acetylenes by group 5 and 6 transition metal catalysts proceeds through the metathesis mechanism, suitable olefins should serve as chain transfer agents.…”

“…13,14 The living polymerization of 1 was first accomplished by Noyori and coworker in 1994. 63 The excellent ability of an isolated catalyst, (Ph 3 P) 2 (nbd)Rh-C:C-Ph, to achieve quantitative yields of poly(phenylacetylenes) with narrow MWD (M w /M n $ 1.1) in the presence of 4-(N,N-dimethylamino)pyridine (DMAP) was demonstrated.…”

“…51 The living nature of this polymerization was confirmed by the fact that the M n of the polymer increased in direct proportion to monomer consumption in toluene at 0 and À30 8C, while the MWD remained narrow. The cis content of the polymer was evaluated by 13 C NMR spectroscopy. Besides the narrow MWD and high cis stereoregularity, the features of this polymerization include large reaction rate (e.g., completed within 1 min at 0 8C) and rather low initiation efficiency…”

“…In parallel to these catalyst developments, Rh catalysts were found to polymerize monosubstituted acetylenes to give stereoregular cis-transoidal polymers. 12,13 A comprehensive and informative review article has recently been published concerning the living polymerization of substituted acetylenes. 14,15 The above-stated progress of various transition metal-based polymerization catalysts enabled the synthesis of a wide variety of polymers from acetylene derivatives including monosubstituted and disubstituted acetylenes, [8][9][10][11][16][17][18] and a,x-diynes.…”