51306-09-3Relevant academic research and scientific papers
Thermodynamic stabilities of Cu+ and Li+ complexes of dimethoxyalkanes (MeO(CH2)nOMe, n = 2-9) in the gas phase: Conformational requirements for binding interactions between metal ions and ligands
Mishima, Masaaki,Maeda, Hideyuki,Than, Soe,Irie, Maki,Kikukawa, Kiyoshi
, p. 616 - 623 (2007/10/03)
The relative free energy changes for the reaction ML+ = M + + L (M = Cu+ and Li+) were determined in the gas phase for a series of dimethoxyalkanes (MeO(CH2)nOMe, n = 2-9) by measuring the equilibrium constants of ligand-transfer reactions using a FT-ICR mass spectrometry. Stable 1:1 Cu+-complexes (CuL +) were observed when the chain is longer than n = 4 while the 1:2 complexes (CuL2+) were formed for smaller compounds as stable ions. The dissociation free energy for CuL+ significantly increases with increasing chain length, by 10 kcal mol-1 from n = 4 to 9. This increase is attributed to the release of constrain involved in the cyclic conformation of the Cu+-complexes. This is consistent with the geometrical and energetic features of the complexes obtained by the DFT calculations at B3LYP/6-311G level of theory. On the contrary, the corresponding dissociation free energy for LiL+ increases only 3 kcal mol -1 from n = 2 to 9, although the structures of the 1:1 Li +-complexes are also considered to be cyclic. From these results it is concluded that the Cu[MeO(CH2)nOMe]+ requires linear alignment for O-Cu-O, indicating the importance of sd σ hybridization of Cu+ in the first two ligands binding energy, while the stability of the Li+ complex is less sensitive to binding geometries except for the system forming a small ring such as n = 1 and 2. Copyright
Fingerprinting a Transition-Structure Guest by a Building-Block Approach with an Incremental Series of Catalytic Hosts. Structural Requirements for Glyme and α,ω-Dimethoxyalkane Catalyses in N-Methylbutylaminolysis and Butylaminolysis of 4-Nitrophenyl Acetate in Chlorobenzene
Hogan, John C.,Gandour, Richard D.
, p. 55 - 61 (2007/10/02)
Glymes, H-(CH2OCH2)n-H, GLM(n), catalyze butylaminolysis of 4-nitrophenyl acetate in chlorobenzene.Values of kcat/Oxy, where Oxy is the number of oxygens in the catalyst, increase with oligomer length up to triglyme, GLM(4), and then plateau.Optimal catalysis on a per oxygen basis requires a -(CH2OCH2)4-fragment, which suggests a four-point recognition of the secondary ammonium ion of the zwitterionic tetrahedral intermediate (TI) (J.Org.Chem. 1991, 56, 2821-2826).Dissection of individual structural components and reassembly to the same structure of the complexverifies this model.The following kinetic studies of 4-nitrophenyl acetate in chlorobenzene have accomplished the task: (a) methylbutylaminolysis catalyzed by GLM(n), n = 2-4; (b) methylbutylaminolysis catalyzed by α,ω-dimethoxyalkanes, CH3O-(CH2)n-OCH3, DME(n), n = 2-10 and 12; and (c) butylaminolysis catalyzed by DME(n), n = 2-10 and 12.Experiment a has revealed that kcat/Oxy is the same for GLM(2) - GLM(4).Optimal catalysis for breakdown of a zwitterionic TI with one ammonium proton only requires a -(CH2OCH2)2-fragment.Experiment b has shown that kcat/Oxy is largest for DME(2) with the values for the remaining DMEs 2 - 2.5-fold lower.A -CH2CH2- is the best spacer between the two oxygens.Thus, bifurcated hydrogen-bond formation between the two oxygens and the one ammonium proton enhances catalysis.Experiment c has revealed that kcat/Oxy for DME(2) exceeds the remaining DMEs by 3 - 3.6-fold, except for DME(8) and DME(10), which have values of kcat/Oxy only 1.7-fold slower.DME(8), the carba analogue of GLM(4), likely binds the two ammonium protons individually with the two oxygens.DME(10) behaves similarly.GLM(4) catalysis of butylaminolysis identifies -(CH2OCH2)4- as an optimal size.DME(8) catalysis confirms this size, although the two catalysts stabilize the two-proton ammonium ion differently.GLM(4) catalyzes butylaminolysis by forming two bifurcated hydrogen bonds.This suggested structure defines the size of the ammonium ion, which agrees with X-ray structural studies of polyether-ammonium complexes.Mechanistic proposals of butylaminolysis of aryl esters require such an ion.The results of this study confirm the stucture of the ion in the rate-limiting step.This building-block approach is a method for "fingerprinting" ammonium ions in transition structures of ionogenic reactions.
