Hyperbranched polyglycerol supported ruthenium catalysts for ring-closing metathesis

Immobilization of Hoveyda–Grubbs type I and II metathesis catalysts onto hyperbranched polyglycerol has been achieved via two distinct synthetic routes. The catalytic units were either placed at the periphery or the interior of the polymer and catalyst loadings between 0.166 and 0.517 mmol g−1 were achieved. The activity of the catalysts in ring-closing metathesis of variously substituted dienes and the ruthenium leaching into the product was investigated. It was found that the supported second-generation Hoveyda–Grubbs catalyst displayed higher activity than the first-generation analogues and achieved high conversions in only two hours. After the first run, however, longer reaction times were required to reach a reasonable conversion. Ru-leaching was determined by ICP-MS and found to be in the range of 0.2–7.8% of the initial ruthenium content, which corresponds to 28–288 ppm of Ru in the products. Additional treatment with activated charcoal after dialysis was found to be beneficial for Ru-removal.