Synthesis and Characterization of Acetonitrile‐Ligated Transition‐Metal Complexes with Tetrakis(pentafluorophenyl)borate as Counteranions

Cationic polymerization of isobutylene at room temperature

“…As already indicated, in the recent years new polymerization strategies have appeared for the preparation of PIB, which are based on initiator or metal complex systems associated with weakly coordinating anions (WCAs) 34–47…”

“…Since then, a series of nitrile‐ligated metal complexes of the structure [M(RCN) 6 ] 2+ (M = Cr(II), Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II); R = CH 3 , C 6 H 5 ) and [MoCl(NCCH 3 ) 5 ] 2+ incorporating the perfluoroborate WCAs, mainly (1) [B(C 6 F 5 ) 4 ] − , (2) [B{C 6 H 3 (m‐CF 3 ) 2 } 4 ] − and (3) [(C 6 F 5 ) 3 B‐C 3 H 3 N 2 ‐B(C 6 F 5 ) 3 ] − (Fig. 3) were investigated by us for the polymerization of IB at room temperature 38–45…”

“… Structures of the nitrile‐ligated metal cations and perfluoroborate (1–3) and perfluoroalkoxyaluminates (4) WCAs applied for the polymerization of IB. (R = CH 3 or C 6 H 5 and M = corresponding metal center) 34–47…”

“…It was found quickly that the synthesis of HR PIB at room temperature using WCA‐associated metal complexes provides an alternative to the conventional cationic polymerization of IB which is generally carried out in cryogenic temperature (−10 to −100 °C) to suppress the chain transfer reactions 38–46. Since the initial report by Nuyken and coworkers, significant improvements in the polymerization features have been achieved by variation of the central metal in the metal complexes, such as shorter reaction times and the possibility to use nonchlorinated solvents in the polymerization process 38–42…”

“…E.g., with the [Mo(NCCH 3 ) 5 Cl][(C 6 F 5 ) 3 B‐C 3 H 3 N 2 ‐B(C 6 F 5 ) 3 ] 2 complex under optimal conditions ([complex] = 0.5 × 10 −4 mol L −1 ; 2 h) an IB conversion of 67% was achieved, and the product had a M n of 600 g mol −1 , PDI of 1.5, and an exo double bond content of 90% 41, 42. Overall, the central metal of the complexes has been varied widely, and particularly, the first row transition metal complexes ligated with acetonitrile and associated with the [B(C 6 F 5 ) 4 ] − have so far been examined with regard to the homopolymerization of IB at 30 °C 43. In addition, very recently, also the WCAs have been further varied by applying aluminate structures (Fig.…”