Synthesis of Silver(I) and Gold(I) Complexes Containing Enantiopure Pybox Ligands. First Assays on the Silver(I)-Catalyzed Asymmetric Addition of Alkynes to Imines

Dinuclear complexes [Ag₂(CF₃SO₃)­{(S,S)-ⁱPr-pybox}₂]­[CF₃SO₃] (1), [Ag₂(R-pybox)₂]­[X]₂ [R-pybox = 2,6-bis­[4-(S)-isopropyloxazolin-2-yl]­pyridine (S,S)-ⁱPr-pybox and X = PF₆ (2) and BF₄ (3); R-pybox = 2,6-bis­[(3aS,8aR)-8,8a-dihydro-3aH-indeno­[1,2-d]­oxazol-2-yl]­pyridine (3aS,3a′S,8aR,8a′R)-indane-pybox and X = CF₃SO₃ (4)], [Ag₂{(S,S)-ⁱPr-pybox}­{(3aS,3a′S,8aR,8a′R)-indane-pybox}]­[CF₃SO₃]₂ (5), and [Ag₂(R-pybox)₃]­[X]₂ [R-pybox = (3aS,3a′S,8aR,8a′R)-indane-pybox and X = CF₃SO₃ (10), SF₆ (11), and PF₆ (12)] as well as mononuclear complexes [Ag­(R-pybox)₂]­[X] [R-pybox = (S,S)-ⁱPr-pybox and X = SbF₆ (6), PF₆ (7), and BF₄ (8); R-pybox = (3aS,3a′S,8aR,8a′R)-indane-pybox) and X = BF₄ (9)] have been prepared by the reaction of the corresponding silver salts and pybox ligands using the appropriate molar ratio conditions. The first gold­(I)/pybox complex [Au₆Cl₄{(S,S)-ⁱPr-pybox}₄]­[AuCl₂]₂ (13) has been synthesized by the reaction of [AuCl­{S­(CH₃)₂}] and (S,S)-ⁱPr-pybox (1:1 molar ratio) in acetonitrile. The structures of the dinuclear (1, 4, 5, 10, and 11) and mononuclear (6 and 9) silver complexes and the hexanuclear gold complex 13 have been determined by single-crystal X-ray diffraction analysis. These studies have been complemented with a solution-state study by NMR spectroscopy, which included structure elucidation, variable-temperature measurements, and diffusion studies using diffusion-ordered spectroscopy (DOSY; for complexes 1, 4, 10, and 12). Complexes 1, 2, 4, and 10 have been assayed as catalysts in the asymmetric addition of phenylacetylene to N-benzylideneaniline.