Ruthenium carbonyl complexes with pyridine-alkoxide ligands: synthesis, characterization and catalytic application in dehydrogenative oxidation of alcohols

Abstract

Dehydrogenative oxidation of secondary alcohols catalyzed by several new trinuclear ruthenium carbonyl complexes under mild conditions was proposed.

Synthesis and Structures of Ruthenium Carbonyl Complexes Bearing Pyridine-Alkoxide Ligands and Their Catalytic Activity in Alcohol Oxidation

“…In the 1 H NMR spectra of 1a - 1g , the characteristic signal of –OH disappeared and the singlets resonance for the methyne adjacent to oxygen were observed at 5.5–6.1 ppm, which were shifted upfield when compared to those in the free ligands (L1-L7). In the 13 C NMR spectra, the resonance signals around 85–92 ppm correspond to the methynes mentioned above, which are in good accordance with compound [pyC(Me) 2 O] 2 Ru 3 (CO) 8 (δ 87.6 ppm) and [pyCHC 6 H 5 O] 2 Ru 3 (CO) 8 (δ 89.3 ppm), which were previously reported in the literature (Hao et al, 2018b).…”

“…In complexes 1a - 1h , the distances between the two Ru atoms directly connected to the ligands are in the range of 3.0236(10)-3.0516(10) Å, which are comparable to the Ru–Ru bond distances in complexes (μ-OC 6 H 4 OMe-2) 2 Ru 3 (CO) 8 (3.012(1) Å) (Santini et al, 1987) and [PyCH = C(Ph)O] 2 Ru 3 (CO) 8 (3.0693(6) Å) (Ma et al, 2017). The bond lengths of Ru(1)–N(1) varying from 2.252(7) Å to 2.330(14) Å observed in all complexes are slightly longer than those Ru–N bond lengths found in complexes {μ 2 -μ 5 :η 1 -(C 5 H 4 N)(C 9 H 5 )}Ru 3 (CO) 9 [2.164(3) Å] (Chen et al, 2010) and (6-bromopyCMeC 6 H 5 O)Ru 3 (CO) 9 (2.229(4) Å) (Hao et al, 2018b). The Ru(1)–O(1) bond lengths for 1a - 1h are all similar and are in the range of 2.072(3)-2.093(5) Å, showing that the substitutions at 2- or 4- positions of benzene ring have no significant effect on bond lengths.…”

“…However, very few examples were focused on di-or tri-nuclear ruthenium complexes and their applications in organic reactions were limited. Recently, we have reported a series of triruthenium carbonyl complexes and their efficient oxidation behavior toward secondary alcohols, while these Ru compounds showed poor reactivity in oxidation of primary alcohols (Hao et al, 2018a,b, 2019). As part of our continuing efforts in developing novel ruthenium carbonyl complexes and their applications in alcohol oxidation, herein, we reported the synthesis and characterization of several ruthenium carbonyl complexes supported by pyridine-alkoxide ligands and their catalytic properties in the oxidation of primary and secondary alcohols using TBHP as an oxidant.…”

Preparation of trinuclear ruthenium clusters based on piconol ligands and their application in Oppenauer‐type oxidation of secondary alcohols

“…[ 20 ] As shown, all the three complexes consist of a trinuclear cluster coordinated by an indolyl‐pyridinyl‐alcohol ligand, and the three Ru atoms form an isosceles triangle. The Ru‐Ru distances of 1a , 1c , and 1d are in the range of 2.74–2.81 Å, which are similar to those in our previously reported Ru complexes [ 21 ] (2.74–2.82 Å) and slightly longer than that of ~2.73 Å in the Ru 3 (CO) 8 (μ‐OC 6 H 4 OMe‐2) 2 complex. [ 22 ] The Ru─O bond lengths in 1a , 1c , and 1d (2.085(3) Å, 2.071(3) Å, and 2.090(9) Å, respectively) are consistent with that of 2.076(3) Å in (PyCMe 2 O)Ru 3 (CO) 8 complex.…”

Selective oxidation of C (sp3)—H bonds enabled by ruthenium clusters containing pyridine‐alkoxide ligands

“…The distances between Ru(1) and Ru(2) are in the range of 2.7865(7)–2.7952(7) Å, which are similar to those in our previously reported Ru complexes (2.74–2.82 Å). [ 34 ] Three ruthenium atoms formed an approximately isosceles triangle. The bond distances of RuN [2.260(6) Å for 1 , 2.255(7) Å for 2 ; 2.249(6) Å for 3 , 2.260(4) Å for 4 ] are almost equal and are similar to those [2.257(5) Å and 2.186(5)] Å observed in { μ ‐ η 2 ‐CH[(2‐C 5 H 4 N)(N‐C 6 H 5 )] 2 Ru 2 (CO) 4 ( μ ‐CO).…”