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1 Pt II as proton shuttle during C H bond activation in the Shilov process Pietro Vidossich,* a Gregori Ujaque, a Agustí Lledós a a Departament de Química, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Fax: (+) ; Tel: (+) ; vido@klingon.uab.es Supplementary Information 1

2 Computional details Ab initio molecular dynamics (AIMD) simulations were performed according to the Car-Parrinello approach 1 with the CPMD program. 2 The trans-ptcl 2 (H 2 O)(CH 4 ) and cis-ptcl 2 (H 2 O)(CH 4 ) optimized structures were solvated with 32 water molecules in a cubic box of ~10.18 Å edge and treated under periodic boundary conditions. Models of similar sizes were successfully used to model the hydrolysis of cisplatin, 3 the Wacker process 4 and to characterize the Pt II aqua complex. 5 The models initially underwent 500 ps classical MD equilibration (fixing the coordinates of the complex) and the final conformations were used to start the AIMD simulations. A time step of 5 au and a fictitious electron mass of 900 au were used to solve the equations of motion. Simulations were performed at constant temperature coupling the system to a Nose-Hoover thermostat. 6, 7 The reference temperature was set to 350 K in order to guarantee the liquid state of the solvent. 8, 9 AIMD simulations were based on the Becke 10 and Lee-Yang-Parr 11 density functionals (BLYP). This functional has been successfully used to model the hydrolysis of cisplatin. 3, 12 Kohn-Sham 13 valence orbitals were expanded in plane waves with kinetic energy < 70 Ry. Martins-Troullier pseudopotentials were used to describe the core-valence shell electrons interactions. 14 For Cl, C, O and H only valence electrons were described explicitly, whereas for Pt a semicore pseudopotential was used. Metadynamics 15, 16 was performed for the cis-ptcl 2 (H 2 O)(CH 4 ) isomer in order to promote the C-H bond cleavage within the timescale accessible to simulations. The coordination number (see ref 16 for the mathematical formula, p=8, q=14, distance cutoff=1.7 Å) between the methane carbon atom and its four bonded protons was used to activate the process. Metadynamics was performed in the extended lagrangian formalism, 16 coupling the collective variable to a fictitious particle of mass 100 amu by a harmonic potential with force constant 1.5 au. A time dependent biasing potential was built adding gaussian-shaped potential energy functions of width and 0.19 kcal/mol height every 200 molecular dynamics steps. Geometry optimizations were performed for the isolated complexes using the GDIIS 17 method until the largest component of the nuclear gradient was lower than 5 x 10-4 a.u. The models were placed in a supercell and treated as isolated. 18 pka Calculation. As an alternative means of estimating the acidity of the Pt H bond, its pka was computed according to standard methods. 19, 20 The pka is related to the free energy change of the 2

3 dissociation reaction by: pka = ΔG aq /RTln10, where ΔG aq is calculated from the thermodynamic cycle depicted in Scheme 1S. Geometries of trans-ptcl 2 (H 2 O)(CH 4 ) and trans-pthcl 2 (H 2 O) 2 (CH 3 ) were optimized with basis sets def2-tzvpp 21 with the ORCA code. 22 Scalar relativistic effects were accounted for by the ZORA approximation. 23, 24 Free energies of solvation were calculated using the COSMO 25 solvation model using a dielectric constant of ε=80 and atomic radii Pt = 2.01, O = 1.72, Cl = 2.05, C = 2.00, H = 1.30 Å to define the solute cavity. The gas phase deprotonation energy included zero point correction. G gas (H+) was set to kcal/mol, 20 G sol (H + ) to kcal/mol. 26 The pka turned out to be negative (-5.2) pointing to a highly acidic proton. 3

4 On the assignment of the Pt oxidation state. The concept of oxidation state is certainly a fundamental one in chemistry. For a transition metal atom it reflects the d n electron configuration and it would thus appear accessible from quantum chemical calculations which determine the electron distribution within the complex. It turns out that it is not straightforward to assign a formal integer oxidation state to a metal atom from the outcome of electronic structure calculations. 27 Methods based on population analysis schemes 27, 28 as well as methods based on the partitioning of the electron density 29 fail to reproduce integer variations which are expected from one electron reduction/oxidation (actually, this observation was interpreted as a compensation mechanism in the metal-ligand orbital mixing 29 ). Furthermore, the observed variations in the metal charge are dependent on the ligands involved. 28 An electron counting technique is generally used to assign formal oxidation states. Given the Lewis structure of the compound, we assign electrons to atom X going through its X-Y bonds according to the following rules: we count 1 if the bond is covalent, O if the bond is ionic and electronegativity(x) < electronegativity(y), 2 if the bond is ionic and electronegativity(x) > electronegativity(y). A lone pair counts 2. Comparison of the number of electrons assigned to X and the number of its valence electrons gives the oxidation state of X. In order to apply the above technique to the outcome of an electronic structure calculation, we have to decide on the nature of each molecular orbital (MO). We will now show that this MO analysis is facilitated by transforming the standard Kohn-Sham orbitals into a set of maximally localized Wannier functions, as suggested by Sit et al. 30 We illustrate the difference for PtHCl 2 (H 2 O)(CH 3 ) in the gas phase. Electrons belonging to Pt are those in orbitals with predominant Pt character. The assignment may be done by visual inspection. However, to put the analysis on more quantitative grounds, we did the following. We used Bader's Atoms in Molecules theory 31 to determine the Pt atomic basin. We have then integrated the density of each orbital within this basin. The resulting values are listed in Table S1 for both KS and Wannier orbitals (please note orbital numbers cannot be put in correspondence). It may be appreciated that a number of KS orbitals have sizable contributions on Pt. To be noted that four KS orbitals (1, 12, 15 and 18) have Pt populations of about 1. On the contrary, Wannier orbitals 1-4, 18, 23 and 24 are clearly centered on Pt, and we find only two orbitals (12 and 14) with a population of about 1. Of the remaining orbitals, 13, 19 and 22 are the only ones with Pt density > 0.1. This is exactly the bonding situation we would expect in PtHCl2(H2O)(CH3): 7 nonbonding orbitals on Pt, 2 covalent bonds and 3 ionic bonds. 4

5 Please note electron counting would assign 16 electrons to Pt for both KS and Wannier obitals (and the total orbital population on Pt is identical for the two sets of obitals). We close this section emphasizing that the procedure we have followed to assign oxidation states to Pt, recently proposed by Sit et al., 30 is a MO analysis in which the orbitals have been conveniently transformed. We believe this procedure facilitates the analysis, especially for condensed phase systems (as in the present work). Table S1. Integrated orbitals density on Pt for Kohn-Sham molecular orbitals (MO) and Wannier functions. Please note psuedopotentials were used in the calculations (of semicore type for Pt) resulting in 48 electrons in 24 orbitals. MO.1: 1.12 WANNIER.1: 1.93 MO.2: 1.66 WANNIER.2: 1.93 MO.3: 1.77 WANNIER.3: 1.95 MO.4: 1.79 WANNIER.4: 1.92 MO.5: 0.06 WANNIER.5: 0.01 MO.6: 0.50 WANNIER.6: 0.03 MO.7: 0.31 WANNIER.7: 0.04 MO.8: 0.20 WANNIER.8: 0.03 MO.9: 0.06 WANNIER.9: 0.01 MO.10: 0.19 WANNIER.10: 0.03 MO.11: 0.32 WANNIER.11: 0.03 MO.12: 1.25 WANNIER.12: 1.25 MO.13: 0.11 WANNIER.13: 0.15 MO.14: 0.35 WANNIER.14: 1.11 MO.15: 0.87 WANNIER.15: 0.04 MO.16: 0.32 WANNIER.16: 0.02 MO.17: 0.20 WANNIER.17: 0.06 MO.18: 0.91 WANNIER.18: 1.94 MO.19: 0.30 WANNIER.19: 0.51 MO.20: 0.12 WANNIER.20: 0.06 MO.21: 0.31 WANNIER.21: 0.04 MO.22: 1.40 WANNIER.22: 0.51 MO.23: 1.61 WANNIER.23: 1.92 MO.24: 1.74 WANNIER.24:

6 restrained MD time a b c d e unrestrained MD a b c d e Figure S1. The graph shows the evolution of selected distances during five independent ab initio molecular dynamics runs (a to e) of trans-ptcl 2 (H 2 O)(CH 4 ). Each run was started from a conformation obtained from a simulation in which all C-H bonds were restrained around the methane C-H bond equilibrium distance (shown schematically on top of the graph). The chemical scheme on the left is used to color code the lines in the graph: Pt-C black line, C-H red, Pt-H green, O water -H blue. 6

dist. (Å) 4 2 0 0. 5 1 time (ps) 1. 5 2 ; Figure S2. Selected structures were extracted from the AIMD simulation labeled a in Figure S1 (marked with stars on the time bar of the top graph).

7 dist. (Å) time (ps) ; Figure S2. Selected structures were extracted from the AIMD simulation labeled a in Figure S1 (marked with stars on the time bar of the top graph). Solvent molecules were removed and only reactive partners were maintained (shown in the middle panel). The bottom graph shows the energy of each geometry at different levels of theory: PBE 32 (black line), BLYP 10, 11 (red), B3LYP 11, 33 (green) and MP2 (blue line). All electrons calculations were performed with the ORCA program 22 using a 23, 24 TZVP basis set on all atoms and accounting for scalar relativistic effects by the ZORA approximation. 7

8 Figure S3. The graph shows the evolution of selected distances during the ab initio molecular dynamics simulation of cis-ptcl 2 (H 2 O)(CH 4 ): Pt-C black line, C-H red, Pt-H green, O water -H blue. The orange line shows the evolution of the collective variable used in the metadynamics part of the simulation to activate the C-H bond. The collective variable used was the coordination number of the methane carbon atom with its four bonded hydrogen: its value is ~4 for methane and ~3 for the methyl complex. The vertical bar on the time axis represents the moment at which the addition of new terms in the biasing potential was suspended. Please note the biasing potential acts only on the carbon coordination number and not on other degrees of freedom. 8

9 Figure S4. Gas-phase optimized structures of trans-ptcl 2 (H 2 O)(CH 4 ) (left) and cis-ptcl 2 (H 2 O)(CH 4 ) (right). Selected distances are given in Å. 9

10 Figure S5. The nuclear rearrangements taking place during the C H bond cleavage are shown superimposed to the evolution of the relevant Wannier centers (green dots, each representing two valence electrons, with those corresponding to initial and final states shown larger in green and blue, respectively). The figure nicely shows the C H bond transforming into the Pt C bond and a metal orbital progressively moving its centre of gravity towards the proton as the C H bond breaks and the proton is transferred to the Pt. 10

11 Table S2. Atomic charges on Pt according to Bader s 31 / Hirsfeld s 34 partitioning of the electron density of gas-phase optimized structures. cis trans PtCl 2 (OH 2 ) / / PtCl 2 (OH 2 )(CH 4 ) / / HPtCl 2 (OH 2 )(CH 3 ) / / PtCl 4 (OH 2 ) / /

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