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The known compound K[( PO ) 2 Mn(CO) 2 ] ( PO = 2-((diphenylphosphino)methyl)-4,6-dimethylphenolate) (K[ 1 ]) was protonated to form the new Mn( i ) complex ( HPO )( PO )Mn(CO) 2 ( H 1 ) and was determined to have a p K a approximately equal to tetramethylguanidine (TMG). The reduction potential of K[ 1 ] was determined to be −0.58 V vs. Fc/Fc + in MeCN and allowed for an estimation of an experimental O–H bond dissociation free energy (BDFE O–H ) of 73 kcal mol −1 according to the Bordwell equation. This value is in good agreement with a corrected DFT computed BDFE O–H of 68.0 kcal mol −1 (70.3 kcal mol −1 for intramolecular H-bonded isomer). The coordination of the protonated O-atom in the solid-state H 1 was confirmed using FTIR spectroscopy and X-ray crystallography. The phenol moiety is hemilabile as evident from computation and experimental results. For instance, dissociation of the protonated O-atom in H 1 is endergonic by only a few kcal mol −1 (DFT). Furthermore, [ 1 ] − and other Mn( i ) compounds coordinated to PO and/or HPO do not react with MeCN, but H 1 reacts with MeCN to form H 1 + MeCN . Experimental evidence for the solution-bound O-atoms of H 1 was obtained from 1 H NMR and UV-vis spectroscopy and by comparing the electronic spectra of bona fide 16-e − Mn( i ) complexes such as [{ PNP }Mn(CO) 2 ] ( PNP = − N{CH 2 CH 2 (P i Pr 2 )} 2 ) and [( Me3SiOP )( PO )Mn(CO) 2 ] ( Me3Si 1 ). Compound H 1 is only meta-stable ( t 1/2 0.5–1 day) and decomposes into products consistent with homolytic O–H bond cleavage. For instance, treatment of H 1 with TEMPO resulted in formation of TEMPOH, free ligand, and [Mn II {( PO ) 2 Mn(CO) 2 } 2 ]. Together with the experimental and calculated weakened BDFE O–H , these data provide strong evidence for the coordination and hemilability of the protonated O-atom in H 1 and represents the first example of the phenolic Mn( i )–O linkage and a rare example of a “soft-homolysis” intermediate in the bond-weakening catalysis paradigm.
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Efficient photorelease of carbon monoxide from a luminescent tricarbonyl rhenium( i ) complex incorporating pyridyl-1,2,4-triazole and phosphine ligands
Precise control over the production of carbon monoxide (CO) is essential to exploit the therapeutic potential of this molecule. The development of photoactive CO-releasing molecules (PhotoCORMs) is therefore a promising route for future clinical applications. Herein, a tricarbonyl-rhenium( i ) complex ( 1-TPP ), which incorporates a phosphine moiety as ancilliary ligand for boosting the photochemical reactivity, and a pyridyltriazole bidentate ligand with appended 2-phenylbenzoxazole moiety for the purpose of photoluminescence, was synthesized and characterized from a chemical and crystallographic point of view. Upon irradiation in the near-UV range, complex 1-TPP underwent fast photoreaction, which was monitored through changes of the UV-vis absorption and phosphorescence spectra. The photoproducts ( i.e. the dicarbonyl solvento complex 2 and one CO molecule) were identified using FTIR, 1 H NMR and HRMS. The results were interpreted on the basis of DFT/TD-DFT calculations. The effective photochemical release of CO associated with clear optical variations (the emitted light passed from green to orange-red) could make 1-TPP the prototype of new photochemically-active agents, potentially useful for integration in photoCORM materials.
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- Award ID(s):
- 1659782
- PAR ID:
- 10403213
- Date Published:
- Journal Name:
- Dalton Transactions
- Volume:
- 50
- Issue:
- 4
- ISSN:
- 1477-9226
- Page Range / eLocation ID:
- 1313 to 1323
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0DT03577G
