Enantiofacial Control of Planar Chiral Arene Ru Complexes Bearing Tropos Biphenyl Ligands

Abstract

A variety of planar chiral Ru-complexes bearing tropos ortho-substituted biphenyl ligands were synthesized. The planar chirality control of the Ru complexes by enantiopure (R)-H8–DABN selectively gave the thermodynamically stable diastereomers via association of solvents employed.

Controlling the Reactivity of Ruthenium(II) Arene Complexes by Tether Ring-Opening

“…The structural constraints within the closed-tether complex 2 are apparent from the orientation of the two phenyl rings which are almost perpendicular to each other with a dihedral or torsion angle of 85°, in comparison with the smaller biphenyl twists of 54° and 52° in 1·HCl and 3 , respectively. The replacement of the NH 2 group of the pendant arm by a phosphino group does not appear to show structural differences with regard to the biphenyl twists (69−88°). − However, the distances between the centroids of the bound arenes and the ruthenium centers appear to be longer (ranging from 1.684 to 1.791 Å) than in 2 (1.654 Å). Further evidence for the strain within the structure of 2 is the observation that the distance between the central ruthenium atom and the NH 2 group of the pendant arm (2.148 Å) is significantly longer than those of the Ru−N bonds of ethylenediamine in the same complex (2.120 and 2.137 Å).…”

“…The replacement of the NH 2 group of the pendant arm by a phosphino group does not appear to show structural differences with regard to the biphenyl twists (69-88°). [50][51][52][53][54][55][56] However, the distances between the centroids of the bound arenes and the ruthenium centers appear to be longer (ranging from 1.684 to 1.791 A ˚) than in 2 (1.654 A ˚). Further evidence for the strain within the structure of 2 is the observation that the distance between the central ruthenium atom and the NH 2 group of the pendant arm (2.148 A ˚) is significantly longer than those of the Ru-N bonds of ethylenediamine in the same complex (2.120 and 2.137 A ˚).…”

Asymmetric catalysis based on tropos ligands

“…During the course of our research on the chirality control of BIPHEP-Ru complexes, it has been found that the racemic RuCl 2 (biphep)(dmf) n (41) bearing axial chirality could be converted into the racemic RuCl 2 (biphepo) (42) bearing planar chirality; heating (AE)-41 in non-degassed DMF at 100 1C for 24 hours, the arene complex (AE)-42 was obtained in 80% yield via the oxidation of the monophosphine portion, by virtue of tropos nature of the tethered BIPHEPO ligand (Scheme 39). 83 A similar treatment of the atropos BINAP or SEGPHOS counterparts could not be transformed to the corresponding arene complexes (43) due to steric hindrance of tetra-ortho-substituted biphenyl compounds. The tropos nature of biphenyl compounds is the key to provide the planar complexes.…”

“…The tropos di-ortho-substituted biphenyl ligands can be used for the syntheses of various arene Ru complexes (Scheme 40). 83 The complexation of [RuCl 2 (Z 6 -benzene)] 2 and two equivalents of the tropos biphenyl ligands (44) at room temperature initially led to the benzene-Ru-complexes (45) quantitatively. The intramolecular ligand exchange between benzene and arene moiety promoted at higher temperature to provide the Scheme 38 DPBP-Ru complex as asymmetric catalysts.…”

“…Planar chirality control of the corresponding dicationic arene Ru complexes by using chiral diamine (R)-H 8 -DABN was thus examined to transform the less favorable diastereomer into the favorable one (Table 14). 83 The complexation of (AE)-42 or (AE)-46 and (R)-H 8 -DABN (1 eq.) in the presence of AgOTf (2 eq.)…”