A Ruthenium(II) Complex with a C₂-Symmetric Diphosphine/Diamine Tetradentate Ligand for Asymmetric Transfer Hydrogenation of Aromatic Ketones

Abstract

The trans-RuIICl2 complexes with structurally similar N,N‘-bis[o-(diphenylphosphino)benzylidene]cyclohexane-1,2-diamine and N,N‘-bis[o-(diphenylphosphino)benzyl]cyclohexane-1,2-diamine ligands have been synthesized, and their molecular structures have been determined. The C 2-symmetric diphosphine/diamine-based Ru complex acts as an excellent catalyst precursor in asymmetric transfer hydrogenation of acetophenone in a 0.1 M 2-propanol solution, leading to 2-phenylethanol in 97% ee and in 93% yield after 7 h at 45 °C. This transfer hydrogenation is characterized by low reversibility under these conditions.

Ligand Design for Catalytic Asymmetric Reduction

“…Precatalysts C1-C3 use the ''NH effect'' described above. [111][112][113] A turnover frequency, defined as moles of product per mol of catalyst per hour, of 30,000 h À1 is achieved by using of C2 and an alkaline base in 2-propanol. 112 A Rh complex C3 is an isolobal to the corresponding arene-Ru complex (see Figure 1.23).…”

A molecular mechanics investigation of the structures and energetics of two classes of Ru(II) complexes with applications in homogeneous catalysis

“…Figure 11 compares the optimized crystal structure of complex G with the original experimental structure (5). Figure 12 compares the molecular structures.…”

“…Complex 2 ( Figure 1b) is structurally reminiscent of the salen catalysts, consisting of the tetradentate ligand N, N -bis-[o-(diphenylphosphino)benzyl]cyclohexane-1,2-diamine (or related species with different substituents at the P atoms) coordinating a Ru(II) centre with two monodentate ligands in trans formation. It has been shown to be an excellent catalytic precursor in asymmetric transfer hydrogenation (5). We will refer to these complexes as "class 1" and "class 2" throughout this paper.…”

New dinuclear arene ruthenium complexes with P,S- or P,O-chelating ligands

“…In the crystal structure, there is no meaningful interaction between complex 4 and the tetrafluoroborates and the chloroform molecules. Poor quality crystals of 5 have been obtained by a slow evaporation of a CDCl 3 solution, and for comparison only, the molecular structure of [5][Cl] 2 is presented, see Fig. 7.…”

“…Diphosphine ligands have been used in particular for the synthesis of catalysts for allylic alkylation [2] and for methanol carbonylation [3]. Tetradentate C 2 -symmetric ligands, possessing two phosphine groups and two other heteroatoms which increase the electron density at the metal centre, have been intensively studied [3][4][5][6][7]. Ligands of this type have been prepared to optimise the catalytic potential of their transition metal complexes [3].…”