J. Volbeda, P. Jones, M. Tamm
Oct 1, 2014
Citations
1
Influential Citations
24
Citations
Journal
Inorganica Chimica Acta
Abstract
Abstract 2-Chloro-1,3-diisopropyl-4,5-dimethylimidazolium tetrafluoroborate ( 1 ) serves as a convenient starting material for the preparation of mono- and bis(imidazolin-2-imine) ligands. Thus, the reaction of two equivalents of 1 with 1,2-ethylenediamine in the presence of potassium fluoride afforded the bis(2-aminoimidazolium) salt [BL i Pr H 2 ][BF 4 ] 2 ( 2 ), from which the achiral bis(imidazolin-2-imine) ligand N , N ′ - bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,2-ethanediamine (BL i Pr ) can be obtained by deprotonation. Likewise, the reaction of 1 with (1 R ,2 R )-(−)-1,2-diaminocyclohexane (DACH) gave [DACH(Im i Pr H) 2 ][BF 4 ] 2 ( 3 ) and its deprotonation the chiral, C 2 -symmetric diimine DACH(Im i Pr ) 2 ( 4 ). Under similar conditions, chiral, C 1 -symmetric mono(imidazolin-2-imines) were obtained from the reaction of 1 with one equivalent of (1 R ,2 R )-(−)-1,2-diaminocyclohexane (DACH) or (1 S ,2 S )-(−)-1,2-diphenylethylenediamine (DPEN), which afforded the 2-aminoimidazolium salts [DACH(Im i Pr H)NH 2 ][BF 4 ] ( 5 ) and [DPEN(Im i Pr H)NH 2 ][BF 4 ] ( 6 ), respectively. The reaction of 4 with [(C 6 H 6 )RuCl 2 ] 2 gave ruthenium complex [(C 6 H 6 )Ru{DACH(Im i Pr ) 2 }]Cl 2 , [ 7 ]Cl 2 , which was treated with KPF 6 to form [ 7 ][PF 6 ] 2 . The ligand precursors 5 and 6 were deprotonated in the presence of [(C 6 H 6 )RuCl 2 ] 2 , which resulted in the formation of complexes [(C 6 H 6 )Ru{DACH(Im i Pr )NH 2 }Cl]Cl [ 8] Cl and [(C 6 H 6 )Ru{DPEN(Im i Pr )NH 2 }Cl]Cl [ 9] Cl. Complexes [ 7 ][PF 6 ] 2 , [ 8 ]Cl and [ 9 ]Cl were investigated for their ability to catalyze the transfer hydrogenation of acetophenone in isopropanol. Complex [ 8 ]Cl proved to be the most active system, while complex [ 9 ]Cl produced the highest enantioselectivity, albeit of only 27% ee. The molecular structures of [ 7 ][(C 6 H 6 )RuCl 3 ] 2 ·CH 2 Cl 2 , formed as a side product, and of [ 8 ]Cl·acetone were determined by X-ray diffraction analyses.