Functional Precision Polymers via Stereo‐ and Regioselective Polymerization Using Group 6 Metal Alkylidene and Group 6 and 8 Metal Alkylidene N‐Heterocyclic Carbene Complexes

Abstract

The concepts of functional precision polymers and the latest accomplishments in their synthesis are summarized. Synthetic concepts based on chain growth polymerization are compared to iterative synthetic approaches. Here, the term "functional precision polymers" refers to polymers that are not solely hydrocarbon-based but contain functional groups and are characterized by a highly ordered primary structure. If insertion polymerization is used for their synthesis, olefin metathesis-based polymerization techniques, that is, ring-opening metathesis polymerization (ROMP), acyclic diene metathesis (ADMET) polymerization, and the regio- and stereoselective cyclopolymerization of α,ω-diynes are almost exclusively applied. Particularly with regio- and stereospecific ROMP and with cyclopolymerization, the synthesis of tactic polymers and copolymers with high regio-, stereo-, and sequence control can be accomplished; however, it requires carefully tailored transition metal catalysts. The fundamental synthetic concepts and strategies are outlined.

Ruthenium‐Catalyzed Alternating Ring‐Opening Metathesis Copolymerization of Norborn‐2‐ene with Cyclic Olefins

“…[11a,c] NMR spectra were collected on Bruker Avance spectrometers (600, 400 or 300 for 1 H). 1 H and 13 C chemical shifts are listed in parts per million (ppm) and were referenced from the solvent peaks or tetramethylsilane (TMS). 31 P chemical shifts were referenced using H 3 PO 4 as external standard.…”

“…[11c] The resulting NHC salt (A) was deprotonated in situ with potassiumtert-amylate and then reacted with RuCl 2 (PCy 3 ) 2 (= CHPh) (GI) to give the new complex 3 in 51% yield. 1 H and 31 P NMR solution spectra of 3 revealed the presence of only a single isomer which was identified as the rotamer with the benzylidene unit located on the same side as the mesityl group.…”

“…The ring-opening metathesis polymerization (ROMP) mediated by well-defined ruthenium catalysts is nowadays one of the most ubiquitous techniques for the synthesis of polymeric materials. [1] The main advantages of this approach reside in the high functional group tolerance, easy reaction conditions and operational simplicity that have led to the availability of a wide range of macromolecular architectures. [1,2] However, the synthesis of precision polymers [1b] derived from the alternating copolymerization of two different monomers via ROMP, promoted by ruthenium-based catalysts, is still limited.…”

“…[1] The main advantages of this approach reside in the high functional group tolerance, easy reaction conditions and operational simplicity that have led to the availability of a wide range of macromolecular architectures. [1,2] However, the synthesis of precision polymers [1b] derived from the alternating copolymerization of two different monomers via ROMP, promoted by ruthenium-based catalysts, is still limited. [3][4][5][6][7][8][9] Only a few examples of alternating ROMP copolymers obtained using properly designed catalysts have been reported.…”

Recent progress on NHC-stabilized early transition metal (group 3–7) complexes: Synthesis and applications

“…On the other hand, molybdenum complexes bearing an O-chelating NHC, such as 148 (Figure 14), displayed activity in ROMP catalysis and the structures of the first insertion products (syn/anti, cis/trans) in the ROMP of norbornene derivatives were identified. 139,140,141 This allowed the proposal of a detailed mechanism of the ROMP catalysis and also the synthesis of high cis or high trans polymers by modifying the syn/anti interconversion rates of the catalysts. Mo-and W-based monoalkoxide pyrrolide complexes (also called MAP-type complexes) are efficient catalysts for the ROMP or cross-metathesis reactions.…”