Catalysis Today 192 (2012) 56–62 Contents lists available at SciVerse ScienceDirect Catalysis Today j ourna l ho me p ag e: www.elsevier.com/lo cate/cattod Insights on the mechanistic features of catalytic oxidations of simple and conjugated olefins promoted by VO(acac) 2 /H 2 O 2 system, in acetonitrile: A computational study Massimiliano Aschi a,∗ , Marcello Crucianelli a,∗∗ , Andrea Di Giuseppe a , Corrado Di Nicola b , Fabio Marchetti b a Dipartimento di Chimica, Ingegneria Chimica e Materiali, Università dell’Aquila, via Vetoio, I-67100 Coppito (AQ), Italy b Dipartimento di Scienze Chimiche, Università degli Studi di Camerino, Via S. Agostino 1, I-62032 Camerino (MC), Italy a r t i c l e i n f o Article history: Received 21 September 2011 Received in revised form 5 January 2012 Accepted 9 January 2012 Available online 3 March 2012 Keywords: Oxovanadium complex Olefin catalytic oxidations Hydrogen peroxide Density Functional Theory Reaction mechanisms a b s t r a c t A computational study based on standard Density Functional Theory and polarized continuum model has been carried out for investigating the essential mechanistic features occurring in the catalytic oxida- tion of two model substrates, namely ethylene and 1,3-butadiene, promoted by vanadyl acetylacetonate [VO(acac) 2 ] in the presence of hydrogen peroxide. Results, showing in general a qualitative agree- ment with experimental data carried out on more complex systems, provide quite different scenarios depending on the conditions employed for the reaction. In particular, under thermodynamic control, no selectivity is observed between the two competitive routes, either epoxidation or double bond oxidative cleavage, in both the substrates. On the other hand, under kinetic control, in both systems the double bond oxidative cleavage is always the favored path, although in the case of 1,3-butadiene the difference with the epoxidation route is enhanced, this confirming that the selectivity is sensitive to the nature of the substituent in the vinyl position. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The catalytic oxidation of olefins is of great interest due to the importance of the corresponding oxidation products in the manufacture of both bulk and fine chemicals, especially those obtained under selective and controlled conditions, like epox- ides. In recent years, many efforts have been directed toward the development of new oxidative catalytic processes based on the use of environment friendly and inexpensive oxidants like H 2 O 2 , O 2 and air. These oxidants can be activated by various transi- tion metal containing compounds [1], the most important being based on Mo, W, Re, Mn, V, typically in high oxidation states [1e], working under either homogeneous or heterogeneous cat- alytic conditions [2]. Within this field, there is a growing interest in the study of novel catalytic applications of high-valent vana- dium complexes, also due to the presence of vanadium in several metalloenzymes [3]. As a consequence of their low radius/charge ratio, vanadium centers in high oxidation states, are usually strong ∗ Corresponding author. Tel.: +39 0 862 433775; fax: +39 0 862 433753. ∗∗ Corresponding author. Tel.: +39 0 862 433308; fax: +39 0 862 433753. E-mail addresses: m.aschi@caspur.it (M. Aschi), marcello.crucianelli@univaq.it (M. Crucianelli). Lewis acids, which makes them suitable for the activation of per- oxidic reagents. In addition to the known application as catalytic systems for the epoxidation of olefins [4], soluble and supported oxovanadium complexes showed to efficiently catalyze various oxidative transformation of organic compounds as allylic alco- hols, alkylaromatic compounds, alkanes, sulfides and alcohols [5]. Within the vanadium(IV) chemistry, the vanadyl ion (VO 2+ ) plays a dominant role [6]. Among its complexes, the vanadyl acetylacetonate [VO(acac) 2 ] is certainly the most representative species. Since the first published accounts describing the synthe- sis of [VO(acac) 2 ] [7], the complex has been used extensively as a reagent in organic synthesis and, after early X-ray crystal structure studies [8], it has been the subject of many experimental inves- tigations due to its interesting paramagnetic and physicochemical properties, mainly associated with the 3d 1 electronic configuration [9]. In the last years, computational methods have provided a pow- erful tool to obtain additional informations on the mechanism of oxygen transfer, in the case of many different high valent metal oxo complexes and also for oxovanadium complex derivatives [10]. Following our ongoing interest toward selective catalytic oxida- tion processes promoted by oxovanadium complexes [11], in this 0920-5861/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2012.01.024