A possibility of functionalizing the dinitrogen in a Chatt complex by H 2 : Density functional studies Perumal Balu a,b , Sambath Baskaran a , Venu Kannappan b , Chinnappan Sivasankar a,⇑ a Department of Chemistry, School of Physical, Chemical and Applied Sciences, Pondicherry University, Puducherry 605 014, India b Postgraduate and Research Department of Chemistry, Presidency College, Chennai 600 005, Tamil Nadu, India article info Article history: Received 24 August 2011 Accepted 24 October 2011 Available online 15 November 2011 Keywords: Dinitrogen reduction Chatt complex Ammonia formation Density functional theory Reaction mechanism Molecular hydrogen abstract DFT calculations have been performed to explore the possibility of functionalizing the coordinated N 2 in a Chatt type complex by H 2 , using some suitable organic co-catalysts in a homogeneous fashion. The cal- culated thermodynamic barriers further revealed that there is the possibility to produce ammonia by the reaction of a Chatt type complex with H 2 in different organic solvents. The electronic features of the various intermediates have also been analyzed. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The conversion of dinitrogen to ammonia using transition metal complexes has long been a challenge to inorganic chemists [1–4]. Relevant to this, Chatt et al. reported some 6th group transition metal ion based phosphine complexes to generate ammonia using an external electron and proton source, but not in a catalytic fash- ion [5–7]. Schrock et al. synthesized a Mo III triamidoamine com- plex to convert dinitrogen to ammonia in a catalytic fashion (TON = 4) using LutH + (Lut = 2,6-dimethyl pyridine) and Cp 2 / Cr as a proton and electron source in pentane solvent [8–12]. Similar to the Schrock et al. report, recently Nishibayashi and coworkers reported a Mo 0 –PNP complex which reduced dinitrogen to ammo- nia catalytically (TON = 6) [13]. Hidai et al. reported a remarkable approach for the functional- ization of dinitrogen using a Chatt type complex along with a ruthenium phosphine complex as a co-catalyst in the presence of H 2 [14–17] and demonstrated the direct utilization of molecular hydrogen. Fryzuk et al. reported a zirconium based side on bound dinitrogen complex which was reacted directly with molecular hydrogen to form an N–NH bound zirconium complex [18–26]. Chirik et al. reported the conversion of dinitrogen to ammonia in the presence of H 2 using [(g 5 -C 5 Me 4 H) 2 Zr] 2 (l 2 ,g 2 ,g 2 -N 2 ) [27– 32]. In addition to the experimental efforts, theoretical calculations have also been reported in the literature to provide more insight into the reduction of dinitrogen to ammonia using molecular hydrogen [33,34]. Although several complexes reported in the literature to bind and reduce dinitrogen in the presence of different reagents, until now no catalyst was known in the literature that could reduce dinitrogen to ammonia catalytically in the presence of H 2 at low temperature and pressure in a homogeneous fashion, and this leaves much room for more research. In this report, we determined the free energy profile to under- stand the possibility of functionalizing the dinitrogen in a Chatt type of tungsten dinitrogen complex using molecular hydrogen. Our choice of complex was reported originally by Chatt et al. and then the synthetic method to make a similar tetraphos tungsten dinitrogen complex was modified by Tuczek et al. [35] (Fig. 1). Our DFT studies clearly indicate that there is the feasibility to generate one equivalent of ammonia in different solvents at low temperature and under normal pressure. 2. Computational methods Complexes 1–7 and 3a have been fully optimized at the B3LYP level of theory using the LANL2DZ basis set [36–39]. Vibrational frequency calculations were performed on these optimized struc- tures to confirm the stationary points. A solvent correction (for heptane, toluene and tetrahydrofuran) was performed using the polarized continuum model [40–42]. Natural Population Analysis (NPA) was performed using same level of theory and basis set. A Natural Bond Orbital analysis (NBO) was carried out to understand more about the electronic structure of the model systems. All these 0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2011.10.036 ⇑ Corresponding author. Tel.: +91 413 2654709; fax: +91 413 2656740. E-mail address: siva.che@pondiuni.edu.in (C. Sivasankar). Polyhedron 31 (2012) 676–681 Contents lists available at SciVerse ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly