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‐(Me2NCH2)2C6H2‐N,C,N]−, Z=H, NO2, CF3, CO2H, 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‐(Me2CH2)2C6H3Z (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 “(CH2NMe2)2PtZ” on π‐delocalisation in the pincer system. Mesomerism in PtII pincer systems is probed by computational methods in combination with relationships between DFT data and the Hammett substituent parameter σp. Electron‐withdrawing substituents at the para‐position enhance π‐interaction of the Pt 5dyz orbital with the arene. Model studies allow determination of relative substituent parameters for (CH2NMe2)2PtZ that are consistent with the orbital analysis of mesomerism, NMR studies and an experimentally estimated value for Z=I.