Computational Study of Bridge Splitting, Aryl Halide Oxidative Addition to Pt^II, and Reductive Elimination from Pt^IV: Route to Pincer-Pt^II Reagents with Chemical and Biological Applications

Abstract

Density functional theory computation indicates that bridge splitting of [PtIIR2(μ-SEt2)]2 proceeds by partial dissociation to form R2Pta(μ-SEt2)PtbR2(SEt2), followed by coordination of N-donor bromoarenes (L-Br) at Pta leading to release of PtbR2(SEt2), which reacts with a second molecule of L-Br, providing two molecules of PtR2(SEt2)(L-Br-N). For R=4-tolyl (Tol), L-Br=2,6-(pzCH2)2C6H3Br (pz=pyrazol-1-yl) and 2,6-(Me2NCH2)2C6H3Br, subsequent oxidative addition assisted by intramolecular N-donor coordination via PtIITol2(L-N,Br) and reductive elimination from PtIV intermediates gives mer-PtII(L-N,C,N)Br and Tol2. The strong σ-donor influence of Tol groups results in subtle differences in oxidative addition mechanisms when compared with related aryl halide oxidative addition to palladium(II) centres. For R=Me and L-Br=2,6-(pzCH2)2C6H3Br, a stable PtIV product, fac-PtIVMe2{2,6-(pzCH2)2C6H3-N,C,N)Br is predicted, as reported experimentally, acting as a model for undetected and unstable PtIVTol2{L-N,C,N}Br undergoing facile Tol2 reductive elimination. The mechanisms reported herein enable the synthesis of PtII pincer reagents with applications in materials and bio-organometallic chemistry.