A New Perspective in the Lewis Acid Catalyzed Ring Opening of Epoxides. Theoretical Study of Some Complexes of Methanol, Acetic Acid, Dimethyl Ether, Diethyl Ether, and Ethylene Oxide with Boron Trifluoride

Abstract

Several 1:1, 1:2, and 2:2 complexes between BF3 and CH3OH (Met), CH3COOH (AcA), (CH3)2O (DME), (CH3CH2)2O (DEE), and (CH2)2O (EOX) have been studied using ab initio (MP2) and density functional theory (DFT) (PBE, B3LYP) methods and the 6-311++G(3df,2pd) basis set. Geometrical structures and vibrational frequencies are reported, in most cases, for the first time. A detailed comparison of the vibrational frequencies for the O...BF3 vibrational modes, as well as for the nu(OH) band in the methanol and acetic acid complexes with BF3, is performed, and the theoretical frequency shifts are compared with the available experimental information. Thermochemical properties are calculated by employing counterpoise correction to alleviate the basis set superposition error. The DFT enthalpy of complexation of the 1:1 complexes results in the order of stability (AcA)2>AcA:BF3>DEE:BF3>DME:BF3>Met:BF3>EOX:BF3>(Met)2; in contrast, MP2 shows the noticeable difference that the AcA:BF3 complex is much less stable (similar to Met:BF3). The order of stability shows that, even though acetic acid prefers dimerization to complexation with BF3, the case is exactly the opposite for methanol. In both cases, the interaction of BF3 with the dimer gives rise to very stable trimers. However, in contrast to the interaction of BF3 with the methanol dimer being stronger than that with the monomer, the interaction of BF3 with the acetic acid dimer is weaker than that with the monomer. The relative strength of the complexes, discussed in the context of BF3-catalyzed ring opening of epoxides, suggests that the effect of the catalyst in a nonprotogenic solvent should be more properly ascribed to activation of the nucleophile instead of activation of the epoxide.

A Systematic Study of Functionalized Oxiranes as Initiating Groups for Cationic Polycyclization Reactions

“…Density functional theory calculations indicate that BF 3 coordinates with ethylene oxide out of plane, as though the lone pairs on oxygen are in sp 3 -hybridized orbitals . With substrates such as 22 , there can be two diastereomeric complexes of this sp 3 -hybridization type, as shown in Figure a.…”

Nucleophilic Aliphatic Substitution

“…38 BF 3 forms bimolecular complexes with the lone pairs of electrons on the oxygen of dimethyl and diethyl ethers, MeOH, HOAc, and ethylene oxide. The tightest and loosest complexes are with diethyl ether and ethylene oxide, respectively.…”

“…The suggested mechanism is partially shown in Scheme 18. Both steric and inductive effects of the ortho-substituent affect the stereochemistry of the addition complex (38) and the stereochemistry of the final aziridine.…”

“…Other theoretical studies discussed above include investigations of the potential energy profiles of 18 gas-phase identity S N 2 reactions of methyl substrates using G2 quantum-chemical calculations, 99 the transition structures, and secondary α-deuterium and solvent KIEs for the S N 2 reaction between microsolvated fluoride ion and methyl halides, 66 the S N 2 reaction between ethylene oxide and guanine, 37 the complexes formed between BF 3 and MeOH, HOAc, dimethyl ether, diethyl ether, and ethylene oxide, 38 the testing of a new nucleophilicity scale, 98 the potential energy surfaces for the S N 2 reactions at carbon, silicon, and phosphorus, 74 and a natural bond orbitalbased CI/MP through-space/bond interaction analysis of the S N 2 reaction between allyl bromide and ammonia. 17…”

Complex Formation between Anisole and Boron Trifluoride: Structural and Binding Properties

“…Although studies of C 6 H 5 OCH 3 and BF 3 complexes are largely lacking, there are many experimental and theoretical studies devoted to the formation of BF 3 complexes with other molecules. ,− These include studies of BF 3 complexes with molecules involving nitrogen atoms (such as with NH 3 , − HCN, ,, and C 5 H 5 N), oxygen atoms, ,,− sulfur atoms, , fluorine atoms, , or benzene rings . Because anisole consists of two distinguished parts, a benzene ring and a methoxy group, the studies of BF 3 complexes with molecules such as those mentioned above can provide useful information to the current work and also allow us to make comparisons.…”