Olefin metathesis has evolved towards a powerful tool for the formation of carbon–carbon bonds. The intensive research effort has culminated in the discovery of well-defined ruthenium–carbene catalysts, such as 1st and 2nd generation Grubbs catalysts, indenylidene based catalysts and many more.
In spite of their booming success, variation of NHC ligands has remained rather unexplored, while it is evident that this variation could have a significant influence on the catalytic activity and selectivity. In this report the influence of the sterical hindering implemented in the NHC ligand is described.[1,2,3]
Keeping the benefit of faster initiation induced by the congestion of ligands, the development of a bulky alkylidene ligand instead of a bulky NHC ligand was considered as an alternative strategy to reach the same goal. Here we report the exploration of the steric influence of indenylidene moieties on 1st and 2nd generation indenylidene catalysts and the effect on the catalytic performance.[4,5,6]

[1] N. Ledoux, B. Allaert, S. Pattyn, H. Vander Mierde, C. Vercaemst, F. Verpoort, Chem. Eur. J. 2006, 12, 4654 – 4661.
[2] N. Ledoux, A. Linden, B. Allaert, H. Vander Mierde, F. Verpoort, Adv. Synth. Catal. 2007, 349, 1692 – 1700.
[3] B. Yu, F. B. Hamad, B. Sels, K. Van Hecke, F. Verpoort, Dalton Trans., 2015, DOI: 10.1039/c5dt00967g.
[4] B. Yu, F. B. Hamad, K. Leus, A. A. Lyapkov, K. Van Hecke, F. Verpoort, J. Organomet. Chem., 2015, accepted
[5] B. Yu, Yu Xie, F. B. Hamad, K. Leus, A. A. Lyapkov, K. Van Hecke, F. Verpoort, New J. Chem., (2015), 39, 1858-1867.
[6] B. Yu, Z-X. Luo, F. B. Hamad, K. Leus, K. Van Hecke, and F. Verpoort, Catal. Sci. Technol., 2015 submitted.