The importance of exchange interactions for transition-metal complexes is well recognized, yet poorly understood.[1] This is in particular true for spin states,[2] where two alternative views prevail on its importance for reactivity. Shaik reported the exchange-enhanced reactivity (EER) principle,[3] while Mayer argued[4] for the driving force of the reaction. Experimental verification can be difficult because of uncertainty of the oxidation state of the metal(s), or the presence of Lewis acids.[5-6] Here we report on oxidative stress, which is often connected with ageing, and hence there exists much interest in the effects of antioxidant complexes. Therefore, we studied the mechanism of a catalase reaction of a Mn-salen complex that contains two phases: a first one in which a MnIII-salen complex captures an oxygen from a hydrogen-peroxide to form a high-valent MnV-oxo and water; and a second phase where the MnV-oxo complex converts a second hydrogen-peroxide into water and oxygen. We focus in particular on the importance of spin states for this reaction,[7] and how this affects the mechanism. Most importantly, we will discuss the role of exchange interactions for understanding these properties and how this is determined by the choice of density functional.[8-10] A generalization of these results in terms of a preferred class of density functional approximations will be given, together with an outlook into the future. Part of this work was supported by COST Action CM1305 (ECOSTBio). References [1] M. Swart, 2013, Int. J. Quant. Chem. 113, 2 [2] M. Costas and J. Harvey, Nature Chem. 2013 5, 7 [3] S. Shaik, H. Chen and D. Janardanan, Nature Chem. 2011, 3, 19 [4] C.T. Saouma and J.M. Mayer, Chem. Sci. 2014, 5, 21 [5] M. Swart, Chem. Commun. 2013, 49, 6650 [6] J. Prakash, G.T. Rohde, K.M. Meier, A.J. Jasniewski, K.M. Van Heuvelen, E. Münck and L. Que Jr., J. Am. Chem. Soc. 2015, 137, 3478 [7] A. Romero-Rivera and M. Swart, 2015, submitted [8] M. Swart, Chem. Phys. Lett. 2013, 580, 166 [9] M. Swart, J. Chem. Theory Comput. 2008, 4, 2057 [10] J. Sun, J.P. Perdew and A. Ruzsinszky, Proc. Natl. Acad. Sci. USA 2015, 112, 685

Exchange interactions in transition-metal reactivity: The catalase activity of Mn-salen complexes

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.