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Schlagwörter:
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Zusammenfassung:
Benzothiazolyl hydrazones 1 (H2LPAH) incorporating polycyclic aromatic hydrocarbons (PAHs) have been fabricated as hemilabile scaffolds and elegantly utilized the inbuilt nitrogen donors as a proficient directing group (DG) to bring about ruthenium(ii) assisted C-H activation in PAHs at both the peri and ortho positions. An isomeric pair of organometallics having formula [Ru-II(L-Pyr)(CO)(PPh3)(2)] (peri: 3a, ortho: 5a) have been conveniently prepared by varying the [Ru-II] precursors with H2LPyr. In contrast, only one type of activated product viz. [Ru-II(L-Anc)(CO)(PPh3)(2)] 3b has been obtained with the 9-anthracene derivative of 1, H2LAnc, under analogous reaction conditions. The underlying mechanistic aspects have been elucidated by isolating the thermally unstable intermediates viz. [Ru-II(HLPyr)Cl(CO)(PPh3)(2)] 2a and [Ru-II(HLPyr)H(CO)(PPh3)(2)] 4a in the course of the peri and ortho C-H activation processes, respectively. The coligand (Cl/H) plays a vital role to bring about the C-H activation at the desired positions via formation of either a four- or five-membered metallacycle in 2a and 4a, respectively. The activation process vis-a-vis Ru-C bond formation in 3a can be achieved smoothly from 2a by a thermal transformation route, which proceeds via an initial rupture of the Ru-N-hydrazonyl bond. In contrast, the trans influential hydride coligand prefers a five-membered chelate to avoid confrontation with N-hydrazone in 4a, which in turn furnishes exclusively ortho activation owing to the close approach of the Ru-H bond towards ortho-H in pyrene. The organometallated complexes exhibit oxidative responses at mild potential. EPR and computational studies indicate that the redox activity originates from the ligand-centered orbitals. The observed rich optoelectronic features are analysed primarily as (ILCT)-I-1 admixed with (MLCT)-M-1 components by theoretical means, indicating an appreciable accumulation of electron density over the ligand backbone in their ground states.
