Photo-isomerisation of alkenyl complexes of platinum(ii): structural, spectroscopic, kinetic and computational investigations

Carmen R. Barone, Cecilia Coletti, Ruth J. McQuitty, Nicola J. Farrer, Giuseppe Lorusso, Luciana Maresca, Alessandro Marrone, Giovanni Natile, Concetta Pacifico, Simon Parsons, Nazzareno Re, Peter J. Sadler (+1 others)
2013 Dalton Transactions  
In this work UVA and blue light have been used to study photo-isomerisation about the CvC double bond in complexes of the type [PtCl(-CHvCHAr)(tmeda)] [Ar = C 6 H 5 , (E)-2a; 4-CH 3 O-C 6 H 4 , (E)-2b; 3-NO 2 -C 6 H 4 , (E)-2c; and 3-CH 3 O-C 6 H 4 , (E)-2d]. The progress of the reaction has been monitored by NMR spectroscopy following irradiation of the NMR sample. The NMR data have been complemented with X-ray diffractometric analysis of compounds (E)-2a-c and (Z)-2a. The kinetic data clearly
more » ... indicate that a monomolecular mechanism is operating with the energy of the irradiating light influencing the rate of isomerisation but not the equilibrium composition, which is only slightly in favour of the Z isomer. DFT and TD-DFT theoretical investigations have been carried out to elucidate the nature of the main electronic transitions in the UV-Vis region and the mechanism of the photo-isomerisation reaction appears to proceed through a CvC bond twist process similar to that involved in purely organic molecules such as stilbene. In the Z isomer, one ortho proton of the phenyl group can come close to platinum (Pt⋯H ortho distance of 2.632 Å in (Z)-2a). In the case of 2c, the difference in chemical shift between the two ortho protons varies from 3.30 ppm in the Z isomer, where interaction with Pt is possible, to 0.60 ppm in the E isomer, where such interaction cannot take place. The analysis of the DFT orbitals indicates that the most shifted H ortho is that with a greater positive charge, pointing to an H-bond type of interaction. † Electronic supplementary information (ESI) available: Pdf file: Fig. S1-S8 and Tables S1-S5. CCDC 904374 [(E)-2a], 904375 [(Z)-2a], 904377 [(E)-2b] and 904378 [(E)-2c]. For ESI and crystallographic data in CIF or other electronic format see
doi:10.1039/c3dt32354d pmid:23493918 fatcat:dyxgln7wfbazbatomc6mh6pc7a