Synthesis and Crystal Structure of a Chiral C3-Symmetric Oxygen Tripodal Ligand and Its Applications to Asymmetric Catalysis

Treatment of Na[P(O)(S-BINOL)] (S-BINOL = (S)-(-)-bi-2-naphthol) with [CpCo(CO)I₂] afforded the chiral C₃-symmetric oxygen tripodal ligand Na[Co{P(O)(S-BINOL)}₃] (Na(1)). Recrystallization of Na(1) from acetone/toluene yielded Na(1)(C₆H₁₂O ₂)₂ (C₆H₁₂O₂ = diacetone alcohol), which has been characterized by X-ray diffraction. The solid-state structure of Na-(1)(C₆H₁₂O₂)₂ features a six-coordinated Na with one η² and one η ¹ diacetone alcohol ligand. Treatment of Na(1) with [(η ⁶-p-cymene)RuCl₂]₂, [Ru(CO)Cl(CH=CHPh)(PPh ₃)₃], and [Pr-(OTf)₃] (OTf = triflate) afforded [(η⁶-p-cymene)Ru(1)] [PF₆] (3), [Ru(1)(CO)(CH=CHPh)(PPh₃)] (4), and [Pr(1)₂(OTf)] (5), respectively. Treatment of Na(1) with [Cu(MeCN)₄] [BF₄] in the presence of PhC≡CH and Me₃SiC≡CSiMe₃ afforded [Cu(1)(η²-PhC≡CH)] (6) and [Cu(1)-(η ²-Me₃SiC≡CSiMe₃)] (7), respectively, which have been characterized by X-ray diffraction. In both 6 and 7, the Cu atom exhibits a distorted 2 + 1 tripod ligand coordination with one Cu-O bond significantly longer than the other two. Na(1) has been employed for the Cu-catalyzed enantioselective aziridination of styrene, the Ti-catalyzed azidolysis of cyclohexene oxide, and the allylation of benzaldehyde with allyltrichlorosilane.