Ruthenium–Triazene Complexes as Latent Catalysts for UV‐Induced ROMP

Abstract

Three novel ruthenium(II) complexes, RuX2(IMesH2)[N,N‐diethyl‐N′‐(2‐benzylidene)triazene] [IMesH2 = 1,3‐dimesitylimidazolin‐2‐ylidene; X = Cl– (2), CF3COO– (3), C6F5COO– (4)] are described. Single‐crystal X‐ray structure analysis of compounds 2–4 revealed that the triazene ligand exists in the trans form and that the aryl‐connected nitrogen atom of the triazene binds to the ruthenium atom to form a five‐membered chelate ring. Compounds 2–4 were applied to the UV‐induced ring‐opening metathesis polymerization (ROMP) of cis‐cyclooctene (5) and dicyclopentadiene (6). Whereas all three precatalysts show pronounced thermal latency in the presence of 5 or 6, only compound 2 displays significant photo‐ROMP activity. The photoreactivity of precatalysts 2–4, which decreases with increasing electron‐withdrawing character and with decreasing pKa of the X groups, is discussed and correlated with the X‐ray data of 2–4, with low‐temperature 1H NMR measurements as well as with cyclovoltammetric measurements.

Tailored molybdenum imido alkylidene N‐heterocyclic carbene complexes as latent catalysts for the polymerization of dicyclopentadiene

“…Generally speaking, different approaches to latent precatalysts have been reported for ring‐opening metathesis polymerization (ROMP) so far. One entails the use of ruthenium alkylidene‐based precatalysts bearing strongly chelating groups at the alkylidene . These can be decoordinated thermally or under the action of UV‐light.…”

Remote control grubbs catalysts that modulate ring‐opening metathesis polymerizations

“…Buchmeiser and coworkers also reported a latent ROMP catalyst that was activated upon exposure to light . Triazene‐functionalized Ru complex 20 features a nitrogen atom directly connected to the aryl ring of the benzylidene ligand and thus effectively chelates the metal center in addition to providing further stabilization through resonance.…”

Latent and Delayed Action Polymerization Systems

“…Further examples for N ‐chelating alkylidenes are found in the versatile class of Schiff base derivatives or Grela's more rigid quinoline systems . With a novel Ru–triazene complex, Buchmeiser and co‐workers made a contribution to these N ‐chelating systems ( 58 ). However, in this case, activation of the complex is achieved by irradiation with UV light.…”