Synthesis and Crystal Structure of a Chiral<i>C</i>₃-Symmetric Oxygen Tripodal Ligand and Its Applications to Asymmetric Catalysis

Abstract

Treatment of Na[P(O)( S -BINOL)] ( S -BINOL = ( S )-(−)-bi-2-naphthol) with [CpCo(CO)I 2 ] afforded the chiral C 3 -symmetric oxygen tripodal ligand Na[Co{P(O)( S -BINOL)} 3 ] (Na( 1 )). Recrystallization of Na( 1 ) from acetone/toluene yielded Na( 1 )(C 6 H 12 O 2 ) 2 (C 6 H 12 O 2 = diacetone alcohol), which has been characterized by X-ray diffraction. The solid-state structure of Na( 1 )(C 6 H 12 O 2 ) 2 features a six-coordinated Na with one η 2 and one η 1 diacetone alcohol ligand. Treatment of Na( 1 ) with [(η 6 - p -cymene)RuCl 2 ] 2, [Ru(CO)Cl(CH CHPh)(PPh 3 ) 3 ], and [Pr(OTf) 3 ] (OTf = triflate) afforded [(η 6 - p -cymene)Ru( 1 )][PF 6 ] ( 3 ), [Ru( 1 )(CO)(CH CHPh)(PPh 3 )] ( 4 ), and [Pr( 1 ) 2 (OTf)] ( 5 ), respectively. Treatment of Na( 1 ) with [Cu(MeCN) 4 ][BF 4 ] in the presence of PhC⋮CH and Me 3 SiC⋮CSiMe 3 afforded [Cu( 1 )(η 2 -PhC⋮CH)] ( 6 ) and [Cu( 1 )(η 2 -Me 3 SiC⋮CSiMe 3 )] ( 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.