No Switching\nCooperativity between Coordinated Azo\nLigands on Complexes Having {M<sup>II</sup>(phosphane‑κ<sup>2</sup><i>P</i>)}<sup>2+</sup> (M = Pd, Pt) Scaffolds

A series of square-planar palladium and platinum compounds\nwith <i>cis</i>-blocking phosphanes and terminal azobenzene\nligands\n[M­(dppp)­(azo)<sub>2</sub>]­(OTf)<sub>2</sub> (azo = CN­(C<sub>6</sub>H<sub>4</sub>)-NN-(C<sub>6</sub>H<sub>4</sub>)­CN (<b>iso-cyano</b>), CN­(C<sub>6</sub>H<sub>4</sub>)-NN-(C<sub>6</sub>H<sub>5</sub>) (<b>iso-Ph</b>)) and [{M<sub>2</sub>(tpbz)}­(azo)<sub>4</sub>]­(OTf)<sub>4</sub> (azo = CN­(C<sub>6</sub>H<sub>4</sub>)-NN-(C<sub>6</sub>H<sub>5</sub>) (<b>iso-Ph</b>)) have been synthesized\nand fully characterized. Similarly to the uncoordinated ligands, the\nnew coordination compounds have shown to be photochemically active\nwith respect to their trans-to-cis isomerization process. Their cis-to-trans\nback spontaneous reaction have been studied as a function of solvent,\ntemperature and pressure and the corresponding activation parameters\ndetermined in order to investigate the mechanism of these transformations.\nThe results obtained are indicative of the operation of a rotational\nmechanism with no cooperativity between the azo ligands attached to\nthe same metal. Density functional theory calculations have been carried\nout in order to estimate the relative energies of the different photoisomers\nfor the theoretical interpretation of the experimental data.