33 Full Paper Macromolecular Chemistry and Physics wileyonlinelibrary.com DOI: 10.1002/macp.201200544 Reactivity of the Dicationic Ruthenium– Alkylidene Complex [Ru(DMF) 3 (IMesH 2 )(=CH— 2—(2—PrO)—C 6 H 4 )], 2 + (BF 4 - ) 2 ] in Ring-Opening Metathesis and Cyclopolymerization Benjamin Autenrieth, Emily Baird Anderson, Dongren Wang, Michael R. Buchmeiser* The reactivity of the dicationic Ru–alkylidene complex [Ru(DMF) 3 (IMesH 2 )(—CH—2—(2— PrO)—C 6 H 4 )] 2 + (BF 4 - ) 2 ] ( 1, IMesH 2 = 1,3-dimesitylimidazolin-2-ylidene) in the ring-opening metathesis polymerization (ROMP) of various functional norborn-2-enes as well as in the cyclopolymerization of different 1,6-heptadiynes is reported. Due to its dicationic character, complex 1 is highly electrophilic and possesses high reactivity towards alkenes and 1,6-hep- tadiynes. Generally, a pronounced difference in reactivity between monomers bearing coordi- nating groups and those that lack such moieties is observed. In the presence of ionic monomers containing coordinating anions such as Br - and I - , a rapid change in the nature of the propagating alkylidene from a dicationic to a neutral one is observed. B. Autenrieth, E. B. Anderson, D. Wang, M. R. Buchmeiser Lehrstuhl für Makromolekulare Stoffe und Faserchemie, Institut für Polymerchemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany E-mail: michael.buchmeiser@ipoc.uni-stuttgart.de M. R. Buchmeiser Institut für Textilchemie und Chemiefasern Denkendorf, Körschtalstr. 26, 73770 Denkendorf, Germany centers out of a second, nonpolar, liquid transport phase. In 1, the Ru=C double bond is strongly polarized com- pared with neutral Ru–alkylidene complexes. Evidence for polarization is the observed shift of the alkylidene-signal in the 1 H NMR spectrum from δ = 16.58 ppm (CD 2 Cl 2 ) for the parent second-generation Grubbs-Hoveyda initiator to δ = 19.28 ppm (CD 2 Cl 2 ) in 1, also indicating a strong agostic interaction between the alkylidene-proton and the ruthenium. Such pronounced downfield shifts in the 1 H NMR for the alkylidene proton are also observed for several “pseudohalide”-derivatives of Grubbs- or Grubbs- Hoveyda-type initiators (Table S1, Supporting Informa- tion) [2–8] where a strong polarization of the Ru–alkylidene has been suggested by DFT calculations. [9] Here, we report on the reactivity of 1, which in fact is a rare example of dicationic Ru–alkylidenes, in ring-opening metathesis polymerization (ROMP). However, in view of the strong propensity of the above-mentioned pseudo- halide derivatives of Grubbs- and Grubbs-Hoveyda-type initiators to cyclopolymerize 1,6-heptadiynes, we were 1. Introduction We recently reported on the synthesis of the dicationic Ru–alkylidene complex [Ru(DMF) 3 (IMesH 2 )(=CH—2—(2— PrO)—C 6 H 4 )] 2 + (BF 4 - ) 2 ] ( 1, IMesH 2 = 1,3-dimesityl-imida- zolin-2-ylidene, Figure 1) and its use in cross-metathesis reactions in ionic liquids under continuous biphasic liquid/ liquid conditions. [1] Due to its dicationic character, 1 can be immobilized within a polar liquid phase, for example, an ionic liquid, whereas the reactants diffuse to the catalytic Macromol. Chem. Phys. 2013, 214, 33−40 © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim