Metal Complexes of a Boron‐Dipyrromethene (BODIPY)‐Tagged N‐Heterocyclic Carbene (NHC) as Luminescent Carbon Monoxide Chemodosimeters

Abstract

Several metal complexes with a boron dipyrromethene (BODIPY)-functionalized N-heterocyclic carbene (NHC) ligand 4 were synthesized. The fluorescence in [(4)(SIMes)RuCl2(ind)] complex is quenched (Φ = 0.003), it is weak in [(4)PdI2(Clpy)] (Φ = 0.033), and strong in [(4)AuI] (Φ = 0.70). The BODIPY-tagged complexes can experience pronounced changes in the brightness of the fluorophore upon ligand-exchange and ligand-dissociation reactions. Complexes [(4)MX(1,5-cyclooctadiene)] (M = Rh, Ir; X = Cl, I; Φ = 0.008-0.016) are converted into strongly fluorescent complexes [(4)MX(CO)2] (Φ = 0.53-0.70) upon reaction with carbon monoxide. The unquenching of the Rh and Ir complexes appears to be a consequence of the decreased electron density at Rh or Ir in the carbonyl complexes. In contrast, the substitution of an iodo ligand in [(4)AuI] by an electron-rich thiolate decreases the brightness of the BODIPY fluorophore, rendering the BODIPY as a highly sensitive probe for changes in the coordination sphere of the transition metal.

Systematic Modulation of the Fluorescence Brightness in Boron‐Dipyrromethene (BODIPY)‐Tagged N‐Heterocyclic Carbene (NHC)–Gold–Thiolates

“…[12,13] The azolium salts used for the synthesis of complexes 2, 3,a nd 5 were prepared in good yields using the respectiveb dp(CH 2 ) 5 Br ands uitable imidazoles (Scheme 3). [12,13] The azolium salts used for the synthesis of complexes 2, 3,a nd 5 were prepared in good yields using the respectiveb dp(CH 2 ) 5 Br ands uitable imidazoles (Scheme 3).…”

“…[12,13] The azolium salts used for the synthesis of complexes 2, 3,a nd 5 were prepared in good yields using the respectiveb dp(CH 2 ) 5 Br ands uitable imidazoles (Scheme 3). [12] Complexes 2, 3,a nd 5 were synthesized from the respective azolium salt and [AuCl(Me 2 S)] in as ingle step, following ag eneral procedure for the synthesis of [(NHC)AuCl] complexes. It is likely,t hat the steric bulk of the BODIPY unit hampers the nucleophilic substitution reaction.…”

“…[12] Aryl thiolates are strong electron donors, but were also chosen in view of the high affinity of sulfur to gold. [12] Aryl thiolates are strong electron donors, but were also chosen in view of the high affinity of sulfur to gold.…”

“…[8] Af ew of those complexes were useful for monitoring catalytict ransformations such as cross-coupling reactions, [9] olefin metathesis catalyst initiation, [10] ligand substitution reactions [8e] (Scheme 2a), gold-mediated transformation of alkynes [11] (Scheme 2b)o rc ould be applied as molecular probes for the sensing of small molecules such as CO [12] (Scheme 2c) or H 2 (Scheme2d). [8] Af ew of those complexes were useful for monitoring catalytict ransformations such as cross-coupling reactions, [9] olefin metathesis catalyst initiation, [10] ligand substitution reactions [8e] (Scheme 2a), gold-mediated transformation of alkynes [11] (Scheme 2b)o rc ould be applied as molecular probes for the sensing of small molecules such as CO [12] (Scheme 2c) or H 2 (Scheme2d).…”

Fine‐Tuning the Fluorescence Gain of FRET‐Type (Bodipy)(Bodipy′)‐NHC‐Iridium Complexes for CO Detection with a Large Virtual Stokes Shift

“…Recently, two such molecular probes were developed, which rely on palladium‐catalyzed fluorogenic reactions involving CO (Scheme , middle) . We recently demonstrated that the exchange of a cod ligand in an Ir complex by two CO molecules leads to a pronounced increase in the fluorescence intensity, suitable for CO detection (Scheme , bottom) . However, our previous probe, like most bodipy's, suffers from a small Stokes shift.…”