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Cyclopalladated 3,5‐Disubstituted 2‐(2′‐Pyridyl)pyrroles Complexed to 8‐Hydroxyquinoline or 4‐Hydroxyacridine
Author(s) -
Mastropietro Teresa F.,
Szerb Elisabeta I.,
La Deda Massimo,
Crispini Alessandra,
Ghedini Mauro,
Aiello Iolinda
Publication year - 2013
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201201341
Subject(s) - chemistry , chelation , ligand (biochemistry) , reactivity (psychology) , pyrrole , stereochemistry , quenching (fluorescence) , 8 hydroxyquinoline , nuclear magnetic resonance spectroscopy , medicinal chemistry , crystal structure , crystallography , fluorescence , organic chemistry , receptor , medicine , biochemistry , physics , alternative medicine , pathology , quantum mechanics
Four new complexes of general formula [(L a )Pd(Qui)] ( 1 ), [(L b )Pd(Acr)] ( 2 ), [(L a )Pd(Acr)] ( 3 ) and [(L b )Pd(Acr)] ( 4 ) containing methyl ( 1 , 3 ) or phenyl ( 2 , 4 ) 3,5‐disubstituted chelated 2‐(2′‐pyridyl)pyrrole ligands (HL a,b ) have been synthesized and characterized. For comparative purposes, the analogous 2‐phenylpyridine (HL c ) derivatives, [(L c )Pd(Qui)] ( 5 ) and [(L c )Pd(Acr)] ( 6 ), have also been prepared. Mild synthetic conditions and reduced reaction times can be employed with HL a,b ligands to obtain the products in good yields, proving the higher reactivity of HL a,b compared with HL c in cyclopalladation. Depending on the relative dispositions of the NN/NO ( 1 – 4 ) or CN/NO ( 5 and 6 ) chelating rings, all the complexes can in principle exist as two isomers. However, in each case, only one isomer was observed by 1 H NMR spectroscopy. The crystal structures of 1 , 4 , and 5 reveal the presence of different isomers for different complexes, depending on both the cyclometallating and ancillary ligands. The structures of 1 – 6 allowed us to hypothesize that the ancillary ligand may play a predominant role in the formation of the trans / cis isomers in these systems and that the pyridylpyrrole definitely produces opposite outcomes compared with the 2‐phenylpyridine ligand. Finally, the photophysical properties of 1 – 4 were studied in solution. Although 5 and 6 are emissive, no emission was detected for 1 – 4 under the same conditions, the emission quenching being most likely caused by the thermal deactivating path of the lowest excited state, which results from a combination of the pyridylpyrrole‐localized state with that localized on the NO ligand.