Initiator Control of Conjugated Polymer Topology in Ring-Opening Alkyne Metathesis Polymerization

• Published in: Journal of the American Chemical Society 2016-05, Vol.138 (19), p.6234-6239
• Main Authors: von Kugelgen, Stephen, Bellone, Donatela E, Cloke, Ryan R, Perkins, Wade S, Fischer, Felix R
• Format: Article
• Language: English
• Subjects: Alkynes - chemical synthesis; Alkynes - chemistry; Catalysis; Kinetics; Magnetic Resonance Spectroscopy; Models, Molecular; Molecular Conformation; Molecular Weight; Molybdenum - chemistry; Polymerization; Polymers - chemical synthesis; Polymers - chemistry; X-Ray Diffraction
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.6b02422

Molybdenum carbyne complexes [RCMo­(OC­(CH3)­(CF3)2)3] featuring a mesityl (R = Mes) or an ethyl (R = Et) substituent initiate the living ring-opening alkyne metathesis polymerization of the strained cyclic alkyne, 5,6,11,12-tetradehydrobenzo­[a,e]­[8]­annulene, to yield fully conjugated poly­(o-phenylene ethynylene). The difference in the steric demand of the polymer end-group (Mes vs Et) transferred during the initiation step determines the topology of the resulting polymer chain. While [MesCMo­(OC­(CH3)­(CF3)2)3] exclusively yields linear poly­(o-phenylene ethynylene), polymerization initiated by [EtCMo­(OC­(CH3)­(CF3)2)3] results in cyclic polymers ranging in size from n = 5 to 20 monomer units. Kinetic studies reveal that the propagating species emerging from [EtCMo­(OC­(CH3)­(CF3)2)3] undergoes a highly selective intramolecular backbiting into the butynyl end-group.