Computational Analysis of Mesomerism in para-Substituted mer-NCN Pincer Platinum(II) Complexes, Including its Relationships with Hammett σp Substituent Parameters.

Density Functional Theory studies of square-planar PtII pincer structures, (4-Z-NCN)PtCl ([4-Z-NCN]- =[4-Z-2,6-(Me2 NCH2 )2 C6 H2 -N,C,N]- , Z=H, NO2 , CF3 , CO2 H, CHO, Cl, Br, I, F, SMe, SiMe3 , tBu, OH, NH2 , NMe2 ), enable characterisation of mesomerism for the pincer-Pt interaction. Relationships between Hammett σp substituent parameters of Z and DFT data obtained from NBO6 and AOMix computation are used to probe the interaction of the 5dyz orbital of platinum with π-orbitals of the arene ring. Analogous computation for 2,6-(Me2 CH2 )2 C6 H3 Z (Z=H, CF3 , CHO, Cl, Br, I, F, SMe, SiMe3 , tBu, OH, NH2 ) and (4-H-NCN)PtZ allows an estimation of the relative substituent effects of "(CH2 NMe2 )2 PtZ" on π-delocalisation in the pincer system.