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Copper(I) halides are often added to olefin metathesis reactions to inhibit catalyst degradation, control product isomerization, enhance catalyst activation, or facilitate catalyst dimerization. In each of these examples, the copper salt is presumed to operate as an independent species, separate from the ruthenium center. We have discovered, however, that certain copper salts can form complexes with the ruthenium catalyst itself, forming hetero-bimetallic copper-ruthenium olefin metathesis catalysts. We confirmed the formation of two complexes through single-crystal X-ray crystallography and NMR spectroscopy. The crystal structure revealed the presence of a four-member ring containing ruthenium, carbon, copper, and chlorine or bromine. The hetero-bimetallic catalyst displayed higher latency and lower activity in the ring-opening metathesis polymerization (ROMP) of norbornene compared to analogous monometallic catalysts. For example, norbornene polymerization catalyzed by the monometallic complex reached 80 % conversion after 4 h, but only 12% conversion when catalyzed by the hetero-bimetallic copper-ruthenium complex under the same conditions. Conversion increased to 63 % when the temperature increased to 50 °C for 1 h, indicating that the bimetallic complex retains activity but requires a higher temperature to activate. The formation of these copper-ruthenium bimetallic complexes suggests the possibility of multi-metallic olefin metathesis catalysts, potentially with different activity and properties than their traditional monometallic counterparts. 

We describe the theory and application of SEC-MALS with minimal equations and a focus on synthetic polymer characterization. 

We synthesized bottlebrush polymers with polyaziridine brushes and a polynorbornene backbone by a grafting-through approach. Polyaziridine macromonomers were synthesized by aza-anoinic polymerization of an N -tosylaziridine, initiated with a norbornene-functionalized sulfonamide anion. These macromonomers were then polymerized by ring-opening metathesis polymerization (ROMP) in dichloromethane to produce bottlebrush polymers with molecular weights of 136–456 kDa. To investigate potential macromonomer aggregation that would hinder grafting-through polymerization, we used dynamic light scattering (DLS) to measure the change in macromonomer aggregation and the growth of bottlebrush chains during ROMP. We observed that the macromonomers aggregate in solution, but once ROMP is initiated, these aggregates disperse over the course of the polymerization. This solution behavior appears to be an example of polymerization-induced deaggregation.