Ab Initio Study of the Stability of the Ylide-like Intermediate Methyleneoxonium in the Reaction between Singlet Methylene and Water

Abstract

Highly correlated ab initio molecular orbital calculations have been used to study the energetics and mechanism governing the reaction between the radical 1CH2 and H2O in gas phase and in solution. It was found that methylene reacts in a barrierless fashion to produce the ylide-like intermediate methyleneoxonium, H2C--OH2, which in turn undergoes a 1,2-hydrogen shift to produce CH3OH. Results obtained at the QCISD(T)/6-311++G**//QCISD/6-311++G** level indicate that in the gas phase, the ylide and the transition state are located 6.4 and 4.9 kcal/mol below reactants, respectively, with an intrinsic barrier for the 1,2-hydrogen shift of 1.4 kcal/mol. In the presence of the solvent, the ylide remains more stable than reactants by 5.5 kcal/mol, while the energy of the transition state is now 1.96 kcal/mol higher than reactants giving a barrier of 7.49 kcal/mol for the 1,2-hydrogen shift.

DFT investigation on mechanism of dirhodium tetracarboxylate-catalyzed O-H insertion of diazo compounds with H2O

“…Direct decomposition of ylide 6 regenerates catalyst 1 and forms a free oxonium ylide 10. 1,2-H shift of ylide 10 via transition structure 11 produces methanol and its activation energy is 1.2 kcal mol -1 , in good agreement with previous calculation results [49]. The formation of free oxonium ylide 10 is an endoergic process and the energy needed is high, 68.4 kcal mol -1 .…”

Carbene Complexes of Nonmetals

“…[17b,20] The QCISD//MP2 level of theory predicts competitive dissociation and 1,2-H shift of 13 in water. [20] Scheme 5. Rearrangement of ylides As a rule, oxonium ylides of the type R 2 OϪCR 1 R 2 (R ϭ alkyl, aryl) do not rearrange readily.…”

“…The computed bond lengths (Table 1) depend only slightly on the theoretical method (HF, [12Ϫ14] MP2, [13Ϫ18] B3LYP, [17Ϫ19] QCISD [20] ) and the basis set employed. Double-bond character is occasionally assigned to the short CϪX bonds of phosphonium and sulfonium ylides.…”

“…N 155Ϫ159 1.07 [13Ϫ15,18] 147Ϫ150 [c] 1.01 [25] O 171Ϫ183 1.25 [13,17,18,20] P 167Ϫ168 0.89 [12Ϫ14,17,18] 166Ϫ170 [d] 0.91 [23] 170Ϫ173 [c] 0.93 [22] S 164Ϫ168 0.90 [12Ϫ14,17,18] 171Ϫ175 [c] 0.95 [24] I 216Ϫ230 1.00Ϫ1.07 [19] 204Ϫ213 [c] 0.95Ϫ1.00 [26] [a] Computed bond lengths of RnXϪCR 1 R 2 (R, R 1 , R 2 ϭ H, Me) relative to bond lengths of HnXϪCH 3 computed by the same method.…”

“…Although the computed binding energies depend on the method employed (Table 2), [13,17] the following trends are observed: (a) the order of binding energies is O ഠ I Ͻ N ഠ S Ͻ P; (b) ylides Me n XϪCH 2 are more strongly bound than ylides H n XϪCH 2 ; [17c,17d] (c) for ylides H n XϪCR 1 R 2 , the activation energies for 1,2-H shift are lower than the binding energies. [13,17,20] Such species are, at best, fleeting intermediates in the course of XϪH insertion reactions (H n O 79 MP2A…”