(Pyridyl)benzoazole ruthenium(ii) and ruthenium(iii) complexes: role of heteroatom and ancillary phosphine ligand in the transfer hydrogenation of ketones

Abstract

The synthesis and structural characterization of ruthenium complexes supported by 2-(2-pyridyl)benzoazole ligands and their evaluation as catalysts in the transfer hydrogenation of ketones are reported. Reactions of 2-(2-pyridyl)benzoimidazole (L1), 2-(2-pyridyl)benzothiazole (L2) and 2-(2-pyridyl)benzoxazole (L3) with RuCl3·3H2O produced the corresponding complexes [RuCl3(L1)] (1), [RuCl3(L2)] (2) and [RuCl3(L3)] (3), respectively. Similarly, treatment of L1-L3 with RuCl2(PPh3)2 afforded the corresponding Ru(II) complexes [RuCl2(PPh3)2(L1)] (4), [RuCl2(PPh3)2(L2)] (5) and [RuCl2(PPh3)2(L3)] (6), respectively. Solid state structures of 1 and 2 confirmed the bidentate coordination mode of L1 and L2 to ruthenium. (31)P{(1)H} NMR spectroscopy revealed coordination of two PPh3 ligands trans to each other in an octahedral environment in 4-6 as confirmed by the solid state structure of 6. Complexes 1-6 produced active catalysts in the transfer hydrogenation of ketones in 2-propanol at 82 °C. Ruthenium(II) complexes 4-6, containing the PPh3 ligand, exhibited higher catalytic activities than the corresponding ruthenium(III) compounds 1-3. Complexes 1 and 4 of L1 were more active than the corresponding complexes of L2 and L3. Density functional theoretical calculations showed that dipole moments of 1-6 control their catalytic activities.

Fast Transfer Hydrogenation(TH) in Aerobic Condition and Oxidation of Alcohols with N‐Methylmorpholine‐N‐oxide Catalyzed by Ru(II) Ligated with Chalcogenated Pyridines and PPh3

“…The 1 H, 13 C{ 1 H}, 31 P{ 1 H} and 77 Se{ 1 H} NMR spectra of L1-L4 and 1-4 recorded in CDCl 3 and DMSO-d 6 respectively, were found consistent with the structures given in Scheme 1. The spectra are given in Supplementary Information (Figures S1-S24).…”

“…The comparison of 13 C{ 1 H} spectra of complexes 1-4 with those of corresponding ligands corroborates the ligation of L1-L4 inferred above, as signals of C8 in the spectra of 1-4 appear deshielded (∼ 6-12 ppm)with respect to those of the corresponding free ligands. The signal of C6 in 13 C{ 1 H} spectra also shows the trend of deshielding (∼ 2-5 ppm) on complex formation. A singlet was observed at 42.58, 43.33, 49.29 and 51.26 ppm in 31 P{ 1 H} NMR spectra of 1-4 respectively.This suggests that the complexation results in one isomer predominantly, which is probably mer as corraborated by single crystal structures of 1-4.…”

“…The present values are larger than the average value (2.348 (5) Å) reported earlier for RuÀ Cl of (pyridyl)benzoazole-Ru(II) and Ru(III) complexes. [13] Figure 1. ORTEP diagram of 1.…”

Ruthenium (II) complexes bearing thioether‐appended α‐iminopyridine ligands: Arene precursors permit access to κ2‐N,N and κ3‐N,N,S complexes

“…Attempts to isolate and fully characterize this product resulted in decomposition. Although the putative [ L1 ‐Ru(PPh 3 ) 2 Cl] BF 4 was precipitated from CDCl 3 solution by addition of copious Et 2 O, 1 H and 31 P spectral features of this isolated solid in DMSO‐ d 6 solution suggest several phosphorus‐containing species (δ = 50.33, 36.08, 17.40) are formed, likely as a result of solvation . Notably, this complex is different from the [ L1 ‐Ru(PPh 3 )Cl 2 ] observed when L1 is heated in the presence of Ru(PPh 3 ) 3 Cl 2 in benzene …”

“…Although the putative [L1-Ru(PPh 3 ) 2 Cl] BF 4 was precipitated from CDCl 3 solution by addition of copious Et 2 O, 1 H and 31 P spectral features of this isolated solid in DMSO-d 6 solution suggest several phosphorus-containing species (δ = 50.33, 36.08, 17.40) are formed, likely as a result of solvation. [69,70] Notably, this complex is different from the [L1-Ru(PPh 3 )Cl 2 ] observed when L1 is heated in the presence of Ru(PPh 3 ) 3 Cl 2 in benzene. [57] A related complex featuring an outer sphere chloride ligand was prepared by heating L1 and half an equivalent of [Ru(p-cymene)Cl(μ-Cl)] 2 in acetonitrile solution.…”