Synthesis and application of molybdenum (III) complexes bearing weakly coordinating anions as catalysts of isobutylene polymerization

Abstract

Acetonitrile ligated molybdenum (III) complexes of the structure [MoCl(NCCH 3 ) 5 ] 2þ bearing different weakly coordinating anions [B(C 6 F 5 ) 4 ] À (WCA a), [B{C 6 H 3 (m-CF 3 ) 2 } 4 ] À (WCA b) and [(C 6 F 5 ) 3 B-C 3 H 3 N 2 -B(C 6 F 5 ) 3 ] À (WCA c) were applied as homogeneous catalysts of the polymerization of isobutylene. High monomer conversions were obtained in short reaction times (<30 min). The molecular weight of the resulting polyisobutylene is nearly independent of parameters such as temperature, solvent, monomer concentration, but is strongly influenced by the type of WCA and by chain transfer reactions which were observed in these systems. Highly reactive low molecular weight polyisobutylenes (M n < 2000 g/mol) were obtained with a high content of exo double bond end groups as shown by 1 H NMR analysis. Furthermore, experiments were performed to reduce the isomerization of these exo end groups into other internal double bonds by varying the polymerization parameters.

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

“…(3)] for the preparation of an umber useful starting material salts of this anion (Scheme 2). [153] Bridged WCAs of the type [(C 6 F 5 ) 3 M-(m-NH 2 )-B(C 6 F 5 ) 3 ] À (where M = Al or B) are accessible by the reaction of [Li(thf) 4 ][H 2 NB(C 6 F 5 ) 3 ]w ith an equivalent of the corresponding Lewis acid. [144][145][146] Ac lear difference between bridged WCAsf eaturing Lewis acids based on aluminum and boron is that aluminum forms the most stable bridged anion with the hard fluoride ligand bridging,w hereas the softer cyanide ligand has been used for the formation of an umber of bridged WCAsb ased upon the B(C 6 F 5 ) 3 Lewis acid.…”

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…”