A Photoswitchable Olefin Metathesis Catalyst

Abstract

A dithienylethene-functionalized N-heterocyclic carbene-Ru(II) complex was synthesized and found to undergo a reversible photoisomerization which influenced its intrinsic catalytic activity. UV-induced ring-closure enhanced the rate of ringclosing metathesis reactions (k closed /k opened = 1.4−1.7) and attenuated the rate of ring-opening metathesis polymerizations (k closed /k opened = 0.56−0.66). Visible light irradiation promoted cycloreversion and restored the initial activity. The ability to switch between the isomeric states of the catalyst was also utilized to modulate the rate of ongoing olefin metathesis reactions via photoirradiation. A computational investigation revealed how steric and electronic effects separately influence the transition states adopted by each form of the catalyst and afforded activation energies that were in agreement with the relative reaction rate constants determined by experiment.

Non‐Oxido‐Vanadium(IV) Metalloradical Complexes with Bidentate 1,2‐Dithienylethene Ligands: Observation of Reversible Cyclization of the Ligand Scaffold in Solution

“…[47] Recently,t he same group described ap hotoswitchableo lefin metathesis catalyst using a similar NHC ligand. [48] Photochromic and luminescence switching properties of aR e I triscarbonyl complex with dithienylphenanthroline were published by Wing-Wah Yam, Phillips and coworkers. [49,50] However, non-switching coordination complexes with DTE entities werer eported for which no cyclization reaction was observed.…”

Visible‐Light Controlled Divergent Catalysis Using a Bench‐Stable Cobalt(I) Hydride Complex

“…Considerably rarer than the switching of a catalytic process between active and inactive states, is switching selectivity between two different pathways . Indeed, within the area of transition‐metal catalysis, only a handful of examples have been reported.…”

Remote control grubbs catalysts that modulate ring‐opening metathesis polymerizations

“…The development of similar ROMP catalysts bearing photochromic chelates (i.e., systems that undergo a reversible light‐mediated transformation) appropriately tethered to the Ru center may also enable switchable polymerizations . For example, we recently reported a photochromic diarylethene (DAE) functionalized Hoveyda‐Grubbs‐type catalyst with two distinct catalytically‐active states that were accessible upon UV ( λ Irr = 313 nm) or visible ( λ Irr > 500 nm) irradiation . As shown in Figure , exposure of a photoswitchable Ru complex equipped with a DAE‐annulated NHC ( 22 ) to UV radiation promoted the reversible electrocyclic photocyclization of the DAE backbone, which attenuated the donating ability of the NHC ligand .…”

“…22 For example, we recently reported a photochromic diarylethene (DAE) functionalized Hoveyda-Grubbs-type catalyst with two distinct catalytically-active states that were accessible upon UV (k Irr 5 313 nm) or visible (k Irr > 500 nm) irradiation. 66 As shown in Figure 10, exposure of a photoswitchable Ru complex equipped with a DAEannulated NHC (22) to UV radiation promoted the reversible electrocyclic photocyclization of the DAE backbone, which attenuated the donating ability of the NHC ligand. 67,68 Moreover, a combination of NMR and UV-vis spectroscopy indicated that 22 cleanly underwent photoisomerization to generate 23 in high conversion.…”