Amine substitution pattern governs catalytic performance in manganese-PNN ketone hydrogenation

Császár, Zsófia and Nagy, Márta and Gömöry, Ágnes and Kovács, Margit and Bényei, Attila C. and Bakos, József and Farkas, Gergely (2026) Amine substitution pattern governs catalytic performance in manganese-PNN ketone hydrogenation. MOLECULAR CATALYSIS, 601. No. 116139. ISSN 2468-8231

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Abstract

A highly modular synthetic strategy based on the ring opening of propane-1,3-diol cyclic sulfate by the corresponding diamines enabled the straightforward preparation of potentially tridentate phosphine-diamine (PNN) ligands of the general formula Ph2P(CH2)3N(R1)(CH2)2NR2R3 (R1, R2, R3 = H or CH3), featuring amine functionalities with different substitution patterns. Using these novel ligands, manganese(I) complexes of the type [Mn(PNN)(CO)2Br], incorporating the catalytically critical NH subunits in distinct chemical environments, were synthesized and evaluated in the hydrogenation of various ketones under different reaction conditions. Catalysts containing a terminal NH2 unit exhibited significantly higher activity than those bearing NHCH3 or N(CH3)2 moieties. Despite the expected reduction in ligand-metal cooperativity upon N-methylation, the presence of an internal N-methyl group in addition to the terminal amino functionality further enhanced catalytic performance. Density functional theory (DFT) calculations revealed substantial differences in the coordination stereochemistry of the PNN ligands within the catalytically active manganese hydride complexes, which correlate with the observed reactivity trends. The most active catalyst displayed exceptionally high turnover number among PNN-containing manganese complexes in ketone hydrogenation.

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