Coligand driven diverse organometallation in benzothiazolyl-hydrazone derivatized pyrene: ortho vs. peri C–H activation. (6th January 2020)

• Record Type: Journal Article
• Authors: Dinda, Soumitra; Patra, Sarat Chandra; Roy, Subhadip; Halder, Supriyo; Weyhermüller, Thomas; Pramanik, Kausikisankar; Ganguly, Sanjib
• Is Part Of: New journal of chemistry. Volume 44:Number 4(2020)
• Page Start: 1407
• Page End: 1417
• Publication Date: 2020-01-06
• Subjects: Chemistry -- Periodicals; Chimie -- Périodiques; 540
• DOI: 10.1039/c9nj05088d
• Languages: English
• ISSNs: 1144-0546

Abstract

Abstract : Divergent aromatic C–H activation at both ortho and peri positions in polyaromatic hydrocarbons has been successfully accomplished by suitable variation of the coligand. Abstract : Benzothiazolyl hydrazones 1 (H2 L PAH ) 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 H2 L Pyr . 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, H2 L Anc, under analogous reaction conditions. The underlying mechanistic aspects have been elucidated by isolating the thermally unstable intermediates viz . [Ru II (HL Pyr )Cl(CO)(PPh3 )2 ] 2a and [Ru II (HL Pyr )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-à-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–Nhydrazonyl bond. In contrast, the trans influential hydride coligand prefers a five-membered chelate to avoid confrontation with Nhydrazone 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 1 ILCT admixed with 1 MLCT components by theoretical means, indicating an appreciable accumulation of electron density over the ligand backbone in their ground states.