TRANS INFLUENCE AND 1JPtPt IN DINUCLEAR PLATINUM(III) COMPLEXES BY AB INITIO MOLECULAR DYNAMICS AND NATURAL LOCALIZED MOLECULAR ORBITALS

Trans effects play an important role in the action of Pt^II-based anticancer drugs¹ and have been extensively studied in Pt^II complexes.² However, the effect remains underexplored theoretically in the less common Pt^III complexes, where this effect propagates through the metal-metal bond, influencing ligand lability and bond strengths at the opposite metal center. Amidate-bridged dinuclear Pt complexes are particularly interesting in this context, as through-bond trans effects can significantly alter substitution kinetics at axial sites and reaction mechanisms, impacting their catalytic efficiency in selective olefin oxidation reactions.^3,4 These complexes thus serve as an interesting model system for understanding how the trans influence is transmitted through the Pt^III-Pt^III bond, which can be probed by ¹J_PtPt.

In this work, we carried out a combined ab initio molecular dynamics (AIMD) and Natural Localized Molecular Orbital (NLMO) study of the trans influence (or structural trans effect) and its manifestation in ¹J_PtPt for pivalamidate-bridged PtI^III complexes with axial ligands of varying σ-donor strenghts. Car-Parrinello Molecular Dynamics simulations were carried out (Quantum Espresso,⁵ v6.0) with a fictitious electron mass of 450 a.u., time step of 0.12 fs, GGA-PBE functional, ultrasoft pseudopotentials, Grimme’s D2 dispersion correction. Systems were thermalized for 3 ps at 350 K (Nosé-Hoover thermostat), followed by a 30 ps NVE production with explicit solvent (D₂O/ClO^4-) under periodic boundary conditions. Configurations were sampled to compute ensemble-averaged σ-donation via NLMO analysis and ¹J_PtPt PBE0/ZORA Hamiltonian with scalar and spin-orbit relativistic corrections with ADF software.⁶

Our results show quantitatively that strong σ-donor ligands (eg. CH₂THF) polarize the Pt-Pt bond (shifting > 80% density to the opposite Pt center), inducing a Pt^IV-Pt^II mixed valence state. σ-Donor destabilizes axial water coordination and reduces ¹J_PtPt up to 80% when compared to weak ligands (eg. H₂O). Supported by NLMO decomposition analysis, fluctuations in ¹J_PtPt also decrease as the bond weakens and surprisingly indicates that the diminished coupling transmission through the Pt-Pt bonding orbital is due to polarization rather than bond elongation.

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Acknowledgments: We acknowledge the National Laboratory for Scientific Computing (LNCC/MCTI, Brazil, SDumont supercomputer), Centro Nacional de Processamento de Alto Desempenho em São Paulo (CENAPAD-SP), and the Center for Computational Research (CCR) at the University at Buffalo for providing computational HPC resources, FAPESP and CNPq.