Effect of the Structure of the Diamine Backbone of P-N-N-P ligands in Iron(II) Complexes on Catalytic Activity in the Transfer Hydrogenation of Acetophenone
ABSTRACT The asymmetric transfer hydrogenation of aromatic ketones can be efficiently accomplished using catalysts that are based on platinum group metals which are more toxic and less abundant than iron. For that reason the discovery of iron based catalysts for the use in this transformation is important. To address this issue, we synthesized a new series of iron(II)-based precatalysts trans-[Fe(Br)(CO)(PPh(2)CH(2)CH═NCHRCHRN═CHCH(2)PPh(2))]BPh(4) (5a-5d) containing P-N-N-P ligands with the diamines (R,R)-1,2-diaminocyclohexane (a), (R,R)-1,2-diphenyl-1,2-diaminoethane (b), (R,R)-1,2-di(4-methoxyphenyl)-1,2-diaminoethane (c), and ethylenediamine (d) incorporated in the backbone using a convenient one-pot synthesis using readily available starting materials. All of the complexes, when activated with a base, show a very high activity in the transfer hydrogenation catalysis of acetophenone, using 2-propanol as a reducing agent under mild conditions. A comparison of the TOF of complexes 5a-5d show that the catalytic activity of complexes increase as the size of the substituents in the backbone of ligands increases (d < a < b = c).
- Journal of chemical education 02/2015; 92(2):378-381. DOI:10.1021/ed500341p · 1.00 Impact Factor
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ABSTRACT: The N2P2 macrocyclic ligands (5S,8S,13E,14aS,18aS,19E)-5,8-diphenyl-5,6,7,8,14a,15,16,17,18,18a-decahydro-tribenzo[b,f,l][1,4,8,11]diazadiphosphacyclotetradecine ((1S,4S,9S,10S)-1a) and (5E,7R,8R,9E,15S,18S)-7,8,15,18-tetraphenyl-7,8, 15,16,17,18-hexahydrodibenzo[f, I] [1,4,8, 11 diazadiphosphacyclotetradecine ((1S,4S,9R,10R)-1b) were prepared by condensing the new, enantiomerically pure synthon 2,2'-((1S, 1'S)-ethane-1,2-diylbis(phenylphosphinediyl))dibenzaldehyde ((S,S)-8), prepared in six steps from (2R,4S,5R)3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidine-2-borane (3)), with (1S,2S)-cyclohexane-1,2-diamine and (1R,2R)-1,2-diphenylethane-1,2-diamine under high-dilution conditions. The opposite enantiomers of the diamines gave oligomeric products. The stereospecificity of the macrocyclization reaction is explained by conformational analysis based on the X-ray structures of (1S,4S,9S,10S)-1a and (1S,4S,9R,10R)-1b. The corresponding diamino macrocycles (1S,4S,9S,10S)-2a and (1S,4S,9R,10R)-2b were prepared by reduction of the imine moiety of (1S,4S,9S,10S)-1a and (IS,45,9R,10R)-1b, respectively. Macrocycles (1S,4S,9S,10S)-1a, (1S,4S,9R,10R)-1b, and (IS,4S,9S,10S)-2a react with [Fe(OH2)(6)](BF4)(2) in acetonitrile to give the corresponding stable, diamagnetic bis(acetonitrile) complexes [Fe(MeCN)(2)(1)1(BF4)(2) (9a and 9b) and [Fe(MeCN)(2)(2a)](BF4)(2) (10a). Complex 9a exists as a 3:1 mixture of trans and Lambda-cis-beta isomers, whereas 9b and 10a adopt the Lambda-cis-beta configuration exclusively. The bis(acetonitrile) complexes are versatile precursors and were used to prepare the bromocarbonyl analogues [FeBr(CO)(1)]BPh4 (11a and 11b).Organometallics 08/2014; 33(15):4086-4099. DOI:10.1021/om5005989 · 4.25 Impact Factor
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ABSTRACT: The preparation of optically pure secondary alcohols in the presence of catalysts based on chiral ligands derived from monoterpenes, such as pinenes, limonenes and carenes, is reviewed. A wide variety of these ligands has been synthesized and used in several catalytic reactions, including hydrogen transfer, CC bond formation via addition of organozinc compounds to aldehydes, hydrosilylation, and oxazaborolidine reduction, leading to high activities and enantioselectivities.Chemistry - A European Journal 10/2014; 21(4). DOI:10.1002/chem.201404303 · 5.93 Impact Factor