(Arene)ruthenium Complexes with Bis(oxazolines): Synthesis and Applications as Asymmetric Catalysts for Diels−Alder Reactions

Reaction of the dimers [RuCl2(arene)]2 (arene = benzene, p-cymene, mesitylene) with bis(oxazolines) (N-N = bis(2-oxazoline) (box), 2,2-bis(2-oxazolinyl)propane (bop), 1,2-bis(2-oxazolinyl)benzene (benbox)) in the presence of NaSbF6 gives the complexes [RuCl(N-N)(arene)][SbF6] (1−8), which have been fully characterized. Treatment of these cations with AgSbF6 generates dications which in some cases are enantioselective catalysts for Diels−Alder reaction of methacrolein and cyclopentadiene. Two complexes, [RuCl(iPr-benbox)(p-cymene)][SbF6] (5) and [Ru(OH2)(iPr-bop)(mes)][SbF6]2 (10; mes = mesitylene), have been characterized by X-ray crystallography

Synthesis of New Chiral 2,2‘-Bipyridyl-Type Ligands, Their Coordination to Molybdenum(0), Copper(II), and Palladium(II), and Application in Asymmetric Allylic Substitution, Allylic Oxidation, and Cyclopropanation

A series of chiral bipyridine-type ligands 5−12 has been synthesized via a de novo construction of the pyridine nucleus. The chiral moieties of the ligands originate from the monoterpene realm, namely, pinocarvone (13 → 6, 7, and 9), myrtenal (18 → 5), nopinone (21 → 8 and 10), and menthone (28 → 11 and 12); the first three precursors can be obtained in one step from β- and α-pinene, respectively. Complexes of these ligands with molybdenum(0) (38−40) and copper(II) (41) have been characterized by single-crystal X-ray crystallography. While complex 38 exhibits polymorphism (monoclinic and tetragonal forms crystallize from the same batch), 41 is characterized by a tetrahedrally distorted geometry of the metal coordination. The Mo and Pd complexes exhibit modest asymmetric induction in allylic substitution (43 → 44), and the Cu(I) counterpart of 41, derived from 10 (PINDY) and Cu(OTf)2, shows promising enantioselectivity (49−75% ee) and reaction rate (≥30 min at room temperature) in allylic oxidation of cyclic olefins (47 → 48). The Cu(I) complex of 11 (MINDY) proved effective in cyclopropanation (49 → 50) with up to 72% ee

Synthesis of New Chiral 2,2‘-Bipyridyl-Type Ligands, Their Coordination to Molybdenum(0), Copper(II), and Palladium(II), and Application in Asymmetric Allylic Substitution, Allylic Oxidation, and Cyclopropanation

A series of chiral bipyridine-type ligands 5−12 has been synthesized via a de novo construction of the pyridine nucleus. The chiral moieties of the ligands originate from the monoterpene realm, namely, pinocarvone (13 → 6, 7, and 9), myrtenal (18 → 5), nopinone (21 → 8 and 10), and menthone (28 → 11 and 12); the first three precursors can be obtained in one step from β- and α-pinene, respectively. Complexes of these ligands with molybdenum(0) (38−40) and copper(II) (41) have been characterized by single-crystal X-ray crystallography. While complex 38 exhibits polymorphism (monoclinic and tetragonal forms crystallize from the same batch), 41 is characterized by a tetrahedrally distorted geometry of the metal coordination. The Mo and Pd complexes exhibit modest asymmetric induction in allylic substitution (43 → 44), and the Cu(I) counterpart of 41, derived from 10 (PINDY) and Cu(OTf)2, shows promising enantioselectivity (49−75% ee) and reaction rate (≥30 min at room temperature) in allylic oxidation of cyclic olefins (47 → 48). The Cu(I) complex of 11 (MINDY) proved effective in cyclopropanation (49 → 50) with up to 72% ee

Synthesis of New Chiral 2,2‘-Bipyridyl-Type Ligands, Their Coordination to Molybdenum(0), Copper(II), and Palladium(II), and Application in Asymmetric Allylic Substitution, Allylic Oxidation, and Cyclopropanation

A series of chiral bipyridine-type ligands 5−12 has been synthesized via a de novo construction of the pyridine nucleus. The chiral moieties of the ligands originate from the monoterpene realm, namely, pinocarvone (13 → 6, 7, and 9), myrtenal (18 → 5), nopinone (21 → 8 and 10), and menthone (28 → 11 and 12); the first three precursors can be obtained in one step from β- and α-pinene, respectively. Complexes of these ligands with molybdenum(0) (38−40) and copper(II) (41) have been characterized by single-crystal X-ray crystallography. While complex 38 exhibits polymorphism (monoclinic and tetragonal forms crystallize from the same batch), 41 is characterized by a tetrahedrally distorted geometry of the metal coordination. The Mo and Pd complexes exhibit modest asymmetric induction in allylic substitution (43 → 44), and the Cu(I) counterpart of 41, derived from 10 (PINDY) and Cu(OTf)2, shows promising enantioselectivity (49−75% ee) and reaction rate (≥30 min at room temperature) in allylic oxidation of cyclic olefins (47 → 48). The Cu(I) complex of 11 (MINDY) proved effective in cyclopropanation (49 → 50) with up to 72% ee