Donor‐Flexible Bis(pyridylidene amide) Ligands for Highly Efficient Ruthenium‐Catalyzed Olefin Oxidation

Abstract

An exceptionally efficient ruthenium‐based catalyst for olefin oxidation has been designed by exploiting N,N′‐bis(pyridylidene)oxalamide (bisPYA) as a donor‐flexible ligand. The dynamic donor ability of the bisPYA ligand, imparted by variable zwitterionic and neutral resonance structure contributions, paired with the redox activity of ruthenium provided catalytic activity for Lemieux–Johnson‐type oxidative cleavage of olefins to efficiently prepare ketones and aldehydes. The ruthenium bisPYA complex significantly outperforms state‐of‐the‐art systems and displays extraordinary catalytic activity in this oxidation, reaching turnover frequencies of 650 000 h−1 and turnover numbers of several millions.

Structural, Electronic, and Catalytic Modulation of Chelating Pyridylideneamide Ruthenium(II) Complexes

“…1 H NMR (300 MHz, CD 2 Cl 2 ): δ 8.67 (d, 3 J HH = 7.4 Hz, 2H, CH PYA ), 8.01 (dd, 3 J HH = 7.5, 4 J HH = 1.1 Hz, 1H, CH Ph ), 7.64 (d, 3 J HH = 7.4 Hz, 2H, CH PYA ), 7.52 (dd, 3 J HH = 7.5, 4 J HH = 1.5 Hz, 1H, CH Ph ), 7.21 (td, 3 J HH = 7.5, 4 J HH = 1.5 Hz, 1H, CH Ph ), 6.97 (td, 3 J HH = 7.5, 4 J HH = 1.1 Hz, 1H, CH Ph ), 5.27 (dd, 3 J HH = 5.8, 4 J HH = 1.1 Hz, 1H, CH cym ), 5.19 (dd, 3 J HH = 5.8, 4 J HH = 1.1 Hz, 1H, CH cym ), 5.00 (dd, 3 J HH = 5.8, 4 J HH = 1.1 Hz, 1H, CH cym ), 4.94 (dd, 3 J HH = 5.8, 4 J HH = 1.1 Hz, 1H, CH cym ), 3.63 (s, 3H, NCH 3 ), 2.22 (septet, 3 J HH = 6.9 Hz, 1H, CHMe 2 ), 1.97 (s, 3H, cym-CH 3 ), 0.94 (d, 3 J HH = 6.9 Hz, 3H, CH−CH 3 ), 0.93 (d, 3 J HH = 6.9 Hz, 3H, CH−CH 3 ). 13 O: C,56.89;H,5.27;N,5.77.…”

“…We recently demonstrated the adaptiveness of this ligand in response to the external environment, such as solvent polarity that enhances the relevance of either resonance structure A (apolar solvents) or B (polar solvents), and exploited this donor flexibility to enhance ruthenium-catalyzed transfer hydrogenation 3 and olefin oxidation. 4 Furthermore, this electronic flexibility was used to prepare a series of iridium complexes with phenyl-substituted PYA ligands to increase the efficiency of the iridium center in water oxidation catalysis, transfer hydrogenation of ketones and imines, and the hydrosilylation of alkenes. 5 The straightforward synthesis of PYA ligands provides access to vast opportunities for ligand modifications as a methodology to fine-tune electronic and steric properties of the coordinated metal center for improved catalytic activity.…”

Modular O- vs. N-coordination of pyridylidene amide ligands to iron determines activity in alcohol oxidation catalysis

“…12 Owing to this electronic flexibility, PYA ligands can stabilize multiple oxidation states on a metal center and their use has brought attractive results to precious metal complexes in homogeneous catalysis (Figure 2), such as Pd(pyPYA)Cl2 for cross coupling reactions, 2 Ir(PhPYA)(Cp*)Cl for water oxidation 13 and [Ru(bisPYA)(p-cym)Cl]PF6 for olefin oxidation. 14 Their N-coordination and donor flexibility makes PYA ligands particularly attractive for hard and Earth-abundant first row transition metals, offering the opportunity to stabilize catalytic intermediates of different oxidation states. For example, multidentate nitrogen donor ligands bound to iron have provided attractive catalytic performance for C-H oxidation reactions, 15-17 olefin polymerization, [18][19][20] and olefin oxidation.…”

Triazenolysis of Alkenes: Aza-version of Ozonolysis

“…38 Therefore, alternative approaches to convert C=C to C=O have been developed, including the cycloaddition of aromatic nitro compounds to olefins, 39 Lemieux-Johnson oxidation 40 and various modifications of these reactions. [41][42][43]…”