Development and mechanistic investigation of the manganese(iii) salen-catalyzed dehydrogenation of alcohols

Manganese(iii) salen has been developed as a new catalytic motif for alcohol dehydrogenation and the mechanism has been elucidated.


N-(4-Methylbenzylidene)-cyclohexylamine (Table 3, entry 2)
Following the general procedure for imine synthesis, the product was isolated as a yellow

N-(4-Methoxybenzylidene)-cyclohexylamine (Table 3, entry 3)
Following the general procedure for imine synthesis, the product was isolated as a yellow

N-(4-Phenylbenzylidene)-cyclohexylamine (Table 3, entry 5)
Following the general procedure for imine synthesis, the product was isolated as a pale yellow solid

N-(4-Nitrobenzylidene)-cyclohexylamine (Table 3, entry 7)
Following the general procedure for imine synthesis, the product was isolated as a pale yellow solid

N-(4-Chlorobenzylidene)-cyclohexylamine (Table 3, entry 9)
Following the general procedure for imine synthesis, the product was isolated as a white solid.

N-(2-Naphthalenylmethylene)-cyclohexylamine (Table 3, entry 11)
Following the general procedure for imine synthesis, the product was isolated as a white solid.

N-Benzylidene-tert-octylamine (Table 4, entry 2)
Following the general procedure for imine synthesis, the product was isolated as a clear liquid.

(R)-N-Benzylidene-1-phenylethylamine (Table 4, entry 4)
Following the general procedure for imine synthesis, the product was isolated as a clear liquid.

N-Benzylidene-1,1-diphenylmethylamine (Table 4, entry 6)
Following the general procedure for imine synthesis, the product was isolated as a white solid.

N-Benzylidene-p-anisidine (Table 4, entry 9)
Following the general procedure for imine synthesis, the product was isolated as a white solid.

N-Benzylidene-4-(trifluoromethyl)aniline (Table 4, entry 10)
Following the general procedure for imine synthesis, the product was isolated as a white solid.

1-Cyclohexylpyrrole (Scheme 1)
Following the general procedure for pyrrole synthesis, the product was isolated as a yellow

Computational details
All calculations were performed with the Jaguar 9.9 program package by Schrodinger LLC.
Geometry optimizations were performed using the empirically corrected B3LYP-D3 functional and the LACVP** basis set and core potential on Mn, which employs the 6-31G** basis on all other atoms. All calculations were performed using the unrestricted formalism, and the multiplicity of all Mn complexes was assumed to be the high spin quintet. Analytical Hessians were computed for all intermediates and transition states to confirm that they have none and one imaginary vibrational frequency, respectively. The solvation free energies of all Mn containing structures were calculated using the PBF solver in Jaguar with standard parameters for benzene, using the same basis set and functional as in the geometry optimization. For the molecules that did not contain Mn, we used the SM8 solvation model, and the basis set was slightly smaller, 6-31G*, since this will enable CM4 charges which generate higher accuracy solvation free energies. Finally, the electronic energy was calculated using the larger respectively. This gave giving G ‡ (prot) and giving G ‡ (deut) and the ratio kdeut/kprot = EXP[(G ‡ (deut) -G ‡ (prot))/RT] at 383 K was used to calculate the kinetic isotope effect. This approximates the proton and deuterium to be classical particles, in accordance with the experimental result, which did not give any indication of non-classical behavior. The turnover frequency is the reaction rate (v) divided by the catalyst concentration. For the reaction mechanism in this report we expect the turnover limiting step to be from 15 to 16ts, for which the rate is expected to be v15-16ts = kr [15]. Given that the reactants are present in great excess we assume that [15]