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Iodine catalyzed Mukaiyama-Michael reaction: experimental evaluation of catalytic effect in conjunction with computational study of the reaction mechanism Sanjib Deuri a and Prodeep Phukan a * The catalytic effect of iodine on Mukaiyama-Michael reaction has been evaluated experimentally taking three representative silyl enolates, which react effectively with various a,b-unsaturated ketones in the presence of 10 mol% of iodine giving 1,5-dicarbonyl products in 74%-87% yield. A study on the mechanism of the iodine catalyzed reaction has been carried out by density functional theory at the Becke, three-parameter, Lee-Yang-Parr/6-31G* level considering trihydrosilyl enol ether and acrolein as model system. Although the uncatalyzed reaction occurs through an asynchronous concerted bond formation process, two energetically competitive pathways (one concerted and the other stepwise) are possible for the catalyzed process. Iodine catalyzed MM reaction between methyl vinyl ketone and 1-phenyl-1-(trimethylsilyloxy)-ethylene involves a very low activation barrier compared with that of the simple trihydrosilyl enol ether/acrolein system. Catalytic effect of iodine was further confirmed by highest occupied molecular orbital-lowest unoccupied molecular orbital analysis and reactivity analysis using conceptual density functional theory based reactivity descriptors at Becke, three-parameter, Lee-Yang-Parr/6-31G** level.

Lewis acid-base type interaction between N-heterocyclic carbene (NHC) and tetravalent silicon reagent (SiR) has been investigated computationally. This NHC-Si interaction is of fundamental importance to the understanding of variety of NHC catalyzed organic transformations involving silicon compounds such as cyanosilylation, trifluoromethylsilylation, etc. Geometries of 24 NHCs, 10 silicon reagents, and their 61 Lewis acid-base complexes have been optimized using the B3LYP/6-31+G(d,p) and M05-2X/6-31+G(d,p) level of theory. The strength of NHC-Si interaction has been assessed in terms of binding energy of the complexes, charge transfer (CT) and the length of Si-CNHC bond. Energy decomposition analysis (EDA) and natural bond orbital (NBO) analysis at M052X/6-31+G(d,p) level of theory has been carried out to get a deeper understanding of the nature of bonding and charge delocalization. Proton affinity of the NHCs and fluoride affinity of the SiRs have been calculated and correlated with the binding energy of the resulting complexes.

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We explore here the feasibility of employing molecular iodine as Lewis acid catalyst for Diels-Alder (DA) reaction using conceptual density functional theory (DFT) based reactivity indices and transition state analysis at the DFT (B3LYP)/6-31G(d) level of theory. Catalytic effect of iodine is probed using reactivity indices considering six different substituents for the diene at the 2-position and five different substituents at the 1-position of the olefinic dienophile. Comparison of HOMO diene-LUMO dienophile gap between the catalyzed and uncatalyzed processes confirms catalytic effect of iodine in DA reaction. Mechanistic details of both the uncatalyzed and the iodine catalyzed processes is achieved through transition state analysis for four possible stereoisomeric reactive channels with respect to isoprene-acrolein model reaction. A significant cutback in activation barrier is observed in presence of iodine. Influence of iodine on regioselectivity of the reaction and asynchronicity of bond formation is analyzed using local version of the HSAB principle and philicity index.