title: Photo-isomerisation of alkenyl complexes of platinum(II): structural, spectroscopic, kinetic and computational investigations.
abstract: In this work UVA and blue light have been used to study photo-isomerisation about the C=C double bond in complexes of the type [PtCl(-CH=CHAr)(tmeda)] [Ar = C6H5, (E)-2a; 4-CH3O-C6H4, (E)-2b; 3-NO2-C6H4, (E)-2c; and 3-CH3O-C6H4, (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 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 C=C 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.
authors.affiliation: Dipartimento di Chimica, Università degli Studi Aldo Moro di Bari, Via E. Orabona 4, I-70125 Bari, Italy.
authors.forename: Carmen R
authors.initials: CR
authors.lastname: Barone
authors.forename: Cecilia
authors.initials: C
authors.lastname: Coletti
authors.forename: Ruth J
authors.initials: RJ
authors.lastname: McQuitty
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Farrer
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Lorusso
authors.forename: Luciana
authors.initials: L
authors.lastname: Maresca
authors.forename: Alessandro
authors.initials: A
authors.lastname: Marrone
authors.forename: Giovanni
authors.initials: G
authors.lastname: Natile
authors.forename: Concetta
authors.initials: C
authors.lastname: Pacifico
authors.forename: Simon
authors.initials: S
authors.lastname: Parsons
authors.forename: Nazzareno
authors.initials: N
authors.lastname: Re
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Sadler
authors.forename: Fraser J
authors.initials: FJ
authors.lastname: White
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D010984:Platinum / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory; D013237:Stereoisomerism; D014466:Ultraviolet Rays
chemical_list: D000475:Alkenes; D056831:Coordination Complexes; D011522:Protons; D010984:Platinum