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A Computational Study of the Olefin Epoxidation Mechanism Catalyzed by Cyclopentadienyloxidomolybdenum(VI) Complexes
Author(s) -
ComasVives Aleix,
Lledós Agustí,
Poli Rinaldo
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200902873
Subject(s) - chemistry , catalysis , ethylene , polarizable continuum model , nucleophile , medicinal chemistry , ligand (biochemistry) , olefin fiber , molecule , activation energy , atom (system on chip) , crystallography , stereochemistry , organic chemistry , biochemistry , receptor , computer science , embedded system , solvation
A DFT analysis of the epoxidation of C 2 H 4 by H 2 O 2 and MeOOH (as models of tert ‐butylhydroperoxide, TBHP) catalyzed by [Cp*MoO 2 Cl] ( 1 ) in CHCl 3 and by [Cp*MoO 2 (H 2 O)] + in water is presented (Cp*=pentamethylcyclopentadienyl). The calculations were performed both in the gas phase and in solution with the use of the conductor‐like polarizable continuum model (CPCM). A low‐energy pathway has been identified, which starts with the activation of ROOH (R=H or Me) to form a hydro/alkylperoxido derivative, [Cp*MoO(OH)(OOR)Cl] or [Cp*MoO(OH)(OOR)] + with barriers of 24.9 (26.5) and 28.7 (29.2) kcal mol −1 for H 2 O 2 (MeOOH), respectively, in solution. The latter barrier, however, is reduced to only 1.0 (1.6) kcal mol −1 when one additional water molecule is explicitly included in the calculations. The hydro/alkylperoxido ligand in these intermediates is η 2 ‐coordinated, with a significant interaction between the Mo center and the O β atom. The subsequent step is a nucleophilic attack of the ethylene molecule on the activated O α atom, requiring 13.9 (17.8) and 16.1 (17.7) kcal mol −1 in solution, respectively. The corresponding transformation, catalyzed by the peroxido complex [Cp*MoO(O 2 )Cl] in CHCl 3 , requires higher barriers for both steps (ROOH activation: 34.3 (35.2) kcal mol −1 ; O atom transfer: 28.5 (30.3) kcal mol −1 ), which is attributed to both greater steric crowding and to the greater electron density on the metal atom.