Insights on co-catalyst-promoted enamine formation between dimethylamine and propanal through ab initio and density functional theory study

Journal of Organic Chemistry

Volumn 72, Issue 22, 2007, Pages 8202-8215

  Patil, Mahendra P ^a   Sunoj, Raghavan B ^a  

^a INDIAN INSTITUTE OF TECHNOLOGY BOMBAY   (India)

Author keywords

[No Author keywords available]

Indexed keywords

DEHYDRATION PATHWAYS; DIMETHYLAMINES; ENAMINE FORMATION; MONOFUNCTIONAL ANCILLARY SPECIES;

CATALYST ACTIVITY; DEHYDRATION; DENSITY FUNCTIONAL THEORY; KETONES; MOLECULAR STRUCTURE; PROTON TRANSFER;

AMINES;

DIMETHYLAMINE; ENAMINE; KETONE DERIVATIVE; METHANOL; METHYLVINYL KETONE; PROPIONALDEHYDE; REAGENT; UNCLASSIFIED DRUG;

AB INITIO CALCULATION; ARTICLE; CATALYSIS; CATALYST; CHEMICAL REACTION; CHEMICAL STRUCTURE; DENSITY FUNCTIONAL THEORY; ENTHALPY; MICHAEL ADDITION; PROTON TRANSPORT; REACTION ANALYSIS;

ALDEHYDES; AMINES; CATALYSIS; DIMETHYLAMINES; MODELS, CHEMICAL; MOLECULAR STRUCTURE; QUANTUM THEORY;

EID: 35549012892     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo071004q     Document Type: Article

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125. (a) It is worth taking note of the increasing current interest on the role of additives in improving organocatalytic reactions.
126. (b) See refs 16 and 18.
127. In an earlier study, Williams and co-workers have shown that potential energy terms are more suitable for discussion on the catalytic power of explicit solvents/ancillary species. See ref 12a. Since the focus of the present study is on the role of co-catalyst in reactions carried out under neat conditions, we believe that the free energy terms are more appropriate energy parameters for discussions.
128. See Tables S1-S14 in Supporting Information for full list of AIM data.
129. See Tables S21-S45 in Supporting Information for the complete list of optimized geometrical parameters for various transition states.
130. 1 angles are found to be 159.1 and 154.5°, respectively.
131. (a) The mPW1PW91/6-311+G** barrier is found to be in very good agreement with that obtained at the MP2 as well as CBS-QB3 levels.
132. (b) See Tables S12 and S13 in Supporting Information.
133. See Tables S9 and Figure S2 in the Supporting Information for AIM and bond order analyses for TS-II.
134. (a) Computed barriers at the MP2(full)/6-311+G**//MP2(full)/ 6-31G* level of theory for steps I and II are tabulated in Tables S15-S20 in the Supporting Information.
135. (b) The single-point energy calculations with the 6-311+G** basis sets are avoided within the PCM framework as the diffuse functions could lead to electron density tails outside the solute cavities generated by the molecularly shaped interlocking spheres.
136. -1 is noticed at the mPW1PW91/6-311+G** (L2) level compared to mPW1PW91/6-31G*-(L1). The corresponding changes predicted at the MP2(full)/6-311+G**//MP2(full)/6-31G* level are found to be even larger and also conform with this trend.
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144. In spite of repeated attempts, the desired transition state for dehydration involving two ancillary amines could not be located. The attempts were also repeated at different levels of theory both in the gas phase and with the continuum model.
145. We have tried a number of initial geometries with different orientation of dimethylamine molecules at the different levels of theory. Efforts toward step-wise as well as concerted dehydration processes were also not successful.
146. Complete list of major derealizations identified using the NBO analysis is summarized in Table S46 in the Supporting Information.
147. (a) As these are nontrivial transition states, extended IRC calculations with 30 points each toward reactant and product have been carried out at both at the MP2/6-31G* and mPW1PW91/6-311+G** levels. The structural and energetic information obtained from the IRC calculations for TS-IIg (and TS-IIIg) is summarized in Table S47-S50 in the Supporting Information.
148. (b) This analysis is supported by additional geometry optimizations using the "opt = calcfc" option on the perturbed geometries derived from the transition state by a 10% displacement along the reaction coordinate, on either side of the first-order saddle point. See Computational Methods for further details.
149. We have taken additional care in establishing the existence of an intermediate along the reaction path. In this regard, the IRC runs have also been also performed at the MP2(full)/6-31G* level, in addition to that at the mPW1PW91/6-311+G** level. Search for iminium ion intermediate was not successful with all other transition state models considered for the dehydration step. See Table S48 in Supporting Information.
150. See Figure S4 in the Supporting Information, where the geometry changes in along the IRC trajectory are provided.
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153. The equivalent possibility with methanol (as in TS-IIb) could not be identified. Similarly, the inclusion of a second molecule of dimethylamine in the active mode (as in TS-IIi) was not possible due to severe steric crowding.
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