Platinum Nanoparticle Based Dip‐Catalyst for Facile Hydrogenation of Quinoline, Unfunctionalized Olefins, and Imines

Abstract

AbstractDeveloping a bio‐inspired catalyst with the efficiency of homogeneous catalysts and recyclability similar to heterogeneous catalysts is quite desirable but challenging. Incorporation of metal nanoparticles (<10 nm) on abundant, low‐cost supports from agricultural waste can yield highly active and product‐selective pseudo‐homogeneous catalysts, with attributes such as ease of retrieval for next use, reusability, etc. In this work, the fabrication of an efficient and reusable ‘dip‐catalyst’ by anchoring platinum nanoparticles on white jute plant (Corchorus capsularis) stems (JPS) and its use for the hydrogenation of N‐heteroarenes, unfunctionalized olefins, and imines are described. The catalyst was characterized using XRD, SEM, EDS, TEM, HRTEM, FTIR, and XPS, and TEM shows spherical (average diameter 4–5 nm) non‐agglomerated metal nanoparticles. Catalyst was used for the chemoselective (>99 % selectivity) hydrogenation of quinoline with a quantitative (>99 %) conversion to 1,2,3,4‐tetrahydroquinoline (py‐THQ) under hydrogen at a pressure <30 bar. Also, functional group tolerance is indicated by the quantitative hydrogenation of 6‐chloroquinoline to 6‐chloro‐1,2,3,4‐tetrahydroquinoline, which is a longstanding challenge owing to C−Cl bond cleavage. In the hydrogenation of structurally‐challenging trisubstituted trans‐2‐methyl‐3‐phenyl‐2‐propen‐1‐ol olefins, 64 % conversion and >99 % selectivity was achieved. A series of imines with different chain lengths was also hydrogenated selectively in methanol with >99 % conversion. Density functional theory (DFT) calculations reveal the efficient adsorption of 6‐chloroquinoline on the surface of Pt nanoparticles on Pt@JPS strips in a tilted orientation placing the C−Cl bond away from the metal and allowing facile desorption of 6‐chloro‐1,2,3,4‐tetrahydroquinoline leading to higher chemoselectivity. The spent catalyst can be reused for 12 consecutive cycles without significant damage to the cellulosic surface.