Three new azulene-based substituted pyridinium cations, azulene-1-azo(N-methyl-4‘-pyridinium) (1
+), azulene-1-[(E)-2-(N-methyl-4‘-pyridinium)ethenyl] (2
+), and azulene-1-azo[(N-methyl-5‘-quinolinium)] (3
+) were synthesized, and their crystal structures solved by
X-ray diffraction. A set of crystallographic, spectroscopic, and computational investigations
reveals that, while the pyridinium is a very strong acceptor unit, the azulene counterpart
acts as an extremely efficient electron donor in these chromophores. The static quadratic
hyperpolarizabilities (β0), measured by the hyper Rayleigh scattering method, are equal to
67 × 10-30, 108 × 10-30, and 80 × 10-30 cm5 esu-1, for 1
+, 2
+, and 3
+, respectively. Interestingly, these values are slightly reduced versus those recorded on the related stilbazolium
derivatives built up from the less efficient (dimethylamino)phenyl donor substituent. This
observation suggests that the donor strength of azulene is beyond the point which maximizes
β in the “push−pull” (arylethenyl)pyridinium series. An important charge delocalization in
the ground state is suggested to account for the reduced β value in these chromophores, in
agreement with the calculated charge-transfer properties, Mulliken charges, and experimental solvatochromism. These investigations suggest that azulene could attract an
additional interest in the design of chromophores with cubic optical nonlinearities.
High catalytic activity and selectivity has been demonstrated for the oxidation of both aliphatic and aromatic amines to nitriles under benign conditions with dioxygen or air using the Ru 2 Cl 4 (az-tpy) 2 complex. The conversion was found to be strongly influenced by the alkyl chain length of the reactant with shorter chain amines found to have lower conversions than those with longer chains. Importantly, by using the ruthenium terpyridine complex functionalized with azulenyl moiety at the 4 position of central pyridine core provided a much higher reactivity catalyst compared with a series of ruthenium terpyridine-based ligand complexes reported. Mechanistic studies using deuterated benzylamine demonstrated the importance of RuOH in this reaction.
Ru2Cl4(az-tpy)2 was immobilized within a range of supported ionic liquids on silica. SILP operates as an efficient heterogeneous catalyst in oxidation of long chain linear primary amines to corresponding nitriles.
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