New generations of Hoveyda and bis‐carbene type of ruthenium‐based olefin metathesis catalysts (10 and 12), containing cationic cyclic alkyl amino carbene (CAAC) ligands, have been synthetized. The catalysts show exceptional stability and activity in environmentally benign, protic media. Various olefin metatheses reactions of OH functionalized feedstock (e. g. RCM, ROMP CM) can be carried out at as low as 0.05 mol % catalyst loading in methanol, isopropanol, water or methanol/water solvent mixture, accomplishing the lowest applied catalyst loading reported so far in these media. The facile olefin metathesis of renewable feedstocks including phospholipids (23) and vegetable oils (20) in protic media has also been demonstrated.

One of the most exciting scientific challenges today is the catalytic degradation of non-biodegradable polymers into value-added chemical feedstocks. The mild pyrolysis of polyolefins, including high-density polyethylene (HDPE), results in pyrolysis oils containing long-chain olefins as major products. In this paper, novel bicyclic (alkyl)(amino)carbene ruthenium (BICAACÀ Ru) temperature-activated latent olefin metathesis catalysts, which can be used for catalytic decomposition of long-chain olefins to propylene are reported. These thermally stable catalysts show significantly higher selectivity to propylene at a reaction temperature of 75 °C compared to second generation Hoveyda-Grubbs or CAACÀ Ru catalysts under ethenolysis conditions. The conversion of long-chain olefins (e.g., 1-octadecene or methyl oleate) to propylene via isomerization-metathesis is performed by using a (RuHCl)(CO)(PPh 3 ) 3 isomerization co-catalyst. The reactions can be carried out at a BICAACÀ Ru catalyst loading as low as 1 ppm at elevated reaction temperature (75 °C). The observed turnover number and turnover frequency are as high as 55 000 and 10 000 mol propylene mol catalyst À 1 h À 1 , respectively.

Ammonia borane (AB) has received extensive attention in recent years as an emerging hydrogen storage material due to its high hydrogen density (19.6 wt %), nontoxicity, stability, and water solubility. Although AB itself is stable in water, its catalytic dehydrogenation (2 mol eq) in aqueous media produces borazine whose tandem hydrolytic reaction enables further hydrogen release (1 mol eq). Thus, water serves both as a reaction medium and also a pure hydrogen fuel source (33% of overall released H2). A high capacity and fast homogeneous AB hydrolytic dehydrogenation system is reported using water-soluble CAAC-Ru carbene catalysts (5 and 6). Applying catalyst 6 at 50 ppm (0.015 mM) loading a high TON of 43,600 can be observed; meanwhile, the yield of the released H2 remains high (73%, equal to 2.2 released molH2/molBH3NH3). The evolved hydrogen can achieve 2.9 molH2/molBH3NH3 ([6] = 3.0 mM) and a TON of 86,100 (equal to 1.70 kg H2 (released)/g Ru metal (used)) (10 ppm loading, [6] = 0.003 mM). The energy density of 1.70 kg H2 is equal to that of 6.6 L of gasoline, which is a general consumption for a medium category car/100 km. The reaction yields nonhazardous borates up to 99% yield, which are considered as a recyclable commodity material for hydrogen storage systems. As the metaborate ion (BO2 –)-induced catalyst passivation causing a decrease in accessibility of active sites in heterogeneous catalysis does not occur at homogeneous conditions, the reported high TON values can be achieved within significantly shorter reaction times and lower catalyst concentrations.