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Olefin metathesis is a versatile synthetic tool for the redistribution of alkylidene fragments at carbon-carbon double bonds. This field, and more specifically the development of task-specific, latent catalysts, attracts emerging industrial and academic interest. This tutorial review aims to provide the reader with a concise overview of early breakthroughs and recent key developments in the endeavor to develop latent olefin metathesis catalysts, and to illustrate their use by prominent examples from the literature.

The synthesis of complexes of the general formula Cl 2 Ru-(SIMes)(L)(3-phenylinden-1-ylidene) (5, L = PCy 3 ; 6, L = py; and 7, L = PPh 3 ) from Cl 2 Ru(PR 3 ) 2 (3-phenylinden-1-ylidene) (2a, R = Ph; 2b, R = Cy) is reported. This family of olefin metathesis catalysts was fully characterized ( 1 H, 13 C and 31 P NMR spectroscopy and elemental analysis) and provided excellent activity in the ring-opening metathesis polymerization of 1,5-cyclooctadiene and the ring-closing metathesis of

A ruthenium Schiff base catalyst (5), bearing an N‐heterocyclic carbene ligand, was found to be a latent catalyst for the ring‐opening metathesis polymerization of cis,cis‐1,5‐cyclooctadiene and dicyclopentadiene and is activated efficiently on addition of hydrochloric acid. A benchmark study was performed using the Grubbs first (1), second (2), and third (3) generation catalyst. Results further illustrate that the catalyst can be stored in dicyclopentadiene at a monomer/catalyst ratio of 15,000/1 without any significant polymerization during at least 12 months. After activation of the catalyst with a Brønsted acid, no undesired loss of performance can be detected. This concept of activation can be easily adapted to a Reaction Injection Molding process, and reaction control is obtained via the in situ generation of the cocatalyst as the outcome of the reaction of alcohols with Lewis acids. Insight into the activation mechanism was gained through an in‐depth nuclear magnetic resonance study, and a plausible mechanism is proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 302–310, 2010