Multidentate Pyridyl‐Aminophosphinite and Pyridyl‐Phosphoramidite Ruthenium(II) Complexes: Synthesis, Structure and Application as Levulinic Acid Hydrogenation Pre‐Catalysts

Abstract

Novel multidentate pyridyl‐aminophosphinite (L1) and pyridyl‐phosphoramidite (L2) ligands of N^P^P^N‐donor system have been synthesized via a series of simple steps. The ligands are symmetrical and as a result, their reactions with [Ru(p‐cymene)Cl2]2 and [Ru(benzene)Cl2]2 lead to the formation of four monodentate bimetallic complexes (1–4) that retain the symmetry of the ligands. Meso and racemic mixtures (rac) of bidentate bimetallic complexes 5–8 were formed from the monodentate complexes through coordination of the pyridine nitrogen atoms to the two metal centers. The isomerism occurs at each metal center, which was evidenced by 31P{1H}, 1H NMR spectroscopy and single‐crystal X‐ray diffraction. The complexes were active towards hydrogenation of levulinic acid (LA) to γ‐valerolactone (GVL) using formic acid as the hydrogen source. The complexes are active at relatively low temperatures and are able to perform the hydrogenation in the absence of any additional solvent apart from the reagents to give high TON of 3 600. The catalysts are recyclable up to the fourth cycle, following which 20 % loss of activity is seen.

N-Donor stabilized tin(ii) cations as efficient ROP catalysts for the synthesis of linear and star-shaped PLAsviathe activated monomer mechanism

“…Starting compounds L 1-3 and 1 were prepared according to the literature. [41][42][43] SnCl2, GaCl3 and Sn(OTf)2 were purchased from Sigma Aldrich and used as received. L-lactide was purchased from Sigma-Aldrich and recrystallized from toluene before use.…”

Comparison of mononuclear and dinuclear copper(ii) biomimetic complexes: spectroelectrochemical mechanistic study of their catalytic pathways

“…Compound HL2 was prepared according to the protocol reported in the literature. 27 2-Formyl-6-methoxypyridine (2.74 g, 20 mmol), ethylenediamine (0.60 g, 10 mmol), and MgSO 4 (1 g) were mixed in THF. The reaction mixture was stirred at 50 °C for 4 h. After that, all insoluble materials were filtered off and the THF filtrate was evaporated to dryness.…”

Ruthenium catalyzed transformation of levulinic acid to γ-valerolactone in water

“…37 Makhubela et al reported a dinuclear Ru complex having multidentate pyridyl-aminophosphinite and pyridyl-phosphoramidite ligands ( 12 in Scheme 1) for the transfer hydrogenation of LA using formic acid as a hydrogen source at 120 °C under neat conditions and observed complete conversion of LA in 8 h with a TOF of 123 h −1 . 38 Wildeman et al used a η 4 -(2,3,4,5-tetraphenylcyclopentadienone)-Ru(CO) 3 complex ( 13 in Scheme 1) for LA to GVL transformation under solvent free conditions at 100 °C and 50 bar H 2 pressure and observed a TOF of 144 h −1 . 39 More recently, Hou et al tested a ruthenium hydride complex ( 14 in Scheme 1) for solvent assisted hydrogenation of methyl levulinate to GVL at 100 °C and 10 bar H 2 pressure.…”