Homogeneous Hydrogenation with a Cobalt/Tetraphosphine Catalyst: A Superior Hydride Donor for Polar Double Bonds and N-Heteroarenes

Abstract

The development of catalysts based on earth abundant metals in place of noble metals is becoming a central topic of catalysis. We herein report a cobalt/tetraphosphine complex-catalyzed homogeneous hydrogenation of polar unsaturated compounds using an air-and moisture-stable and scalable precatalyst. By activation with potassium hydroxide, this cobalt system shows both high efficiency (up to 24 000 TON and 12 000 h −1 TOF) and excellent chemoselectivities with various aldehydes, ketones, imines, and even N-heteroarenes. The preference for 1,2reduction over 1,4-reduction makes this method an efficient way to prepare allylic alcohols and amines. Meanwhile, efficient hydrogenation of the challenging N-heteroarenes is also furnished with excellent functional group tolerance. Mechanistic studies and control experiments demonstrated that a Co I H complex functions as a strong hydride donor in the catalytic cycle. Each cobalt intermediate on the catalytic cycle was characterized, and a plausible outer-sphere mechanism was proposed. Noteworthy, external inorganic base plays multiple roles in this reaction and functions in almost every step of the catalytic cycle.

Lithium Bromide/HBpin: A Mild and Effective Catalytic System for the Selective Hydroboration of Aldehydes and Ketones

“…White solid (130 mg, 97% yield); 1 H NMR (400 MHz, CDCl 3 ) δ 7.38 (dt, J = 8.0, 1.8 Hz, 2H), 7.31 (td, J = 6.7, 6.1, 1.7 Hz, 2H), 7.26–7.21 (m, 1H), 6.61 (d, J = 15.9 Hz, 1H), 6.36 (dt, J = 15.9, 5.7 Hz, 1H), 4.32 (d, J = 7.1 Hz, 2H), 1.48 (s, 1H); 13 C NMR (100 MHz, CDCl 3 ) δ 136.75, 131.27, 128.70, 128.57, 127.82, 126.57, 63.87. NMR data were in accordance with reported literature 17 …”

Catalytically Active Co−Nx Species Stabilized on Nitrogen‐doped Porous Carbon for Efficient Hydrogenation and Dehydrogenation of N‐heteroarenes

“…The best KCC‐1@Co−N−C‐800 catalyst has a high TOF value of 8.24 h −1 , which is 3–24 times higher than the values reported in the transition‐metal‐based catalysts towards the base/base‐free catalytic transfer hydrogenation or hydrogenation for quinoline (Table S2), such as homogeneous Co(BF 4 ) 2 ⋅ 6H 2 O, Mn(CO) 5 Br, and [Co II (L1)(CH 3 CN)](BF 4 ) 2 catalysts and heterogeneous Co@NCNTs‐800, Co/Melamine‐2@C‐700, ISAS−Co/OPNC, Co@OMNC‐700, CoOx@CN, Co@NGS‐800 and Co 0 /ZnCl 2 catalysts . A scale‐up experiment was performed to ascertain the practicality of the KCC‐1@Co−N−C‐800 catalyst.…”

Building C(sp3) Molecular Complexity on 2,2′‐Bipyridine and 1,10‐Phenanthroline in Rhenium Tricarbonyl Complexes

“…Metal complexes of group 4 containing the 2,3,4‐trihydro‐1,10‐phenanthroline ligand are efficient precatalysts for olefin polymerization [37] . The main synthetic route to access these complexes involves two steps—first the synthesis of the free ligand can be achieved by metal‐catalyzed partial reduction of phen [6b–f] to yield 1,2,3,4‐tetrahydro‐1,10‐phenanthroline and is followed by treatment with a metal alkyl precursor. In contrast, the strategy reported here for Re complexes avoids the need to use transition‐metal catalysts to access the partially reduced ligand.…”