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. 2024 Sep 2;63(35):16251-16263.
doi: 10.1021/acs.inorgchem.4c02169. Epub 2024 Aug 21.

No Switching Cooperativity between Coordinated Azo Ligands on Complexes Having {MII(phosphane-κ2P)}2+ (M = Pd, Pt) Scaffolds

Ot Raïch Panisello  1 , Jesús Jover  1   2 , Cristina Puigjaner  3 , Montserrat Ferrer  1   4 , Manuel Martínez  1   4
Affiliations

No Switching Cooperativity between Coordinated Azo Ligands on Complexes Having {MII(phosphane-κ2P)}2+ (M = Pd, Pt) Scaffolds

Ot Raïch Panisello et al. Inorg Chem. .

Abstract

A series of square-planar palladium and platinum compounds with cis-blocking phosphanes and terminal azobenzene ligands [M(dppp)(azo)2](OTf)2 (azo = CN(C6H4)-N═N-(C6H4)CN (iso-cyano), CN(C6H4)-N═N-(C6H5) (iso-Ph)) and [{M2(tpbz)}(azo)4](OTf)4 (azo = CN(C6H4)-N═N-(C6H5) (iso-Ph)) have been synthesized and fully characterized. Similarly to the uncoordinated ligands, the new coordination compounds have shown to be photochemically active with respect to their trans-to-cis isomerization process. Their cis-to-trans back spontaneous reaction have been studied as a function of solvent, temperature and pressure and the corresponding activation parameters determined in order to investigate the mechanism of these transformations. The results obtained are indicative of the operation of a rotational mechanism with no cooperativity between the azo ligands attached to the same metal. Density functional theory calculations have been carried out in order to estimate the relative energies of the different photoisomers for the theoretical interpretation of the experimental data.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1
Figure 1
Figure 1
CN(C6H4)-N=N-(C6H4)CN (iso-cyano), and (4-isocyanophenyl)diazenylphenyl, CN(C6H4)-N=N-(C6H5) (iso-Ph) compounds utilized in this work.
Figure 2
Figure 2
Schematic drawing of the [M(dppp)(azo)2]2+ and [{M2(tpbz)}(azo)4]4+ compounds.
Figure 3
Figure 3
View of the XRD-determined [Pd(dppp)(iso-Ph)2]2+ (left) and [Pd(dppp)(iso-cyano)2]2+ (right) structural units (hydrogen atoms, solvent and counteranions not shown for clarity). Selected bond lengths (Å) and angles (°) for [Pd(dppp)(iso-Ph)2]2+: Pd(1)C(28) 2.042(4), Pd(1)C(41) 2.023(4), C(28)N(1) 1.119(5), C(41)N(4) 1.137(5), C(28)Pd(1)C(41) 88.25(18); for [Pd(dppp)(iso-cyano)2]2+: Pd(1)C(1) 2.002(8), Pd(1)C(15) 2.029(9), C(1)N(1) 1.152(11), C(15)N(5) 1.131(12), C(14)N(4) 1.127(12), C(28)N(8) 1.150(12), C(1)Pd(1)C(15) 92.8(3).
Figure 4
Figure 4
UV–vis spectra of the iso-Ph ligand (black) and its [Pd(dppp)(iso-Ph)2]2+ (red, divided by two) and [{Pd2(tpbz)}(iso-Ph)4]4+(olive, divided by four) derivatives in dichloromethane solution.
Figure 5
Figure 5
(a) Changes in the intensity of the UV–vis signal at 340 nm of a dichloromethane solution of [Pt(dppp)(iso-Ph)]2+ on consecutive irradiation cycles at 365 and 450 nm. (b) Full UV–vis time-resolved spectral changes of the same solution on illumination at 365 nm. (c) Initial and final spectrum (after 10 illumination cycles) of the same solution.
Figure 6
Figure 6
COSY 1H–1H NMR spectrum of a solution of [Pd(dppp)(trans-iso-Ph)2]2+ in CD2Cl2 and expansion indicating the proton signals of the ligand in the less predominant cis–trans (c–t) and cis–cis (c–c) complexes.
Figure 7
Figure 7
Calculated energy differences between the structures of the trans-iso-Ph and cis-iso-Ph units in the (a) [Pd(dppp)(iso-Ph)2]2+ and (b) [{Pd2(tpbz)}(iso-Ph)4]4+ complexes.
Figure 8
Figure 8
Eyring plot for the derivation of the activation parameters for the cis-to-trans isomerization process occurring on the system [Pd(dppp)(iso-cyano)2]2+ in different solvents.
Figure 9
Figure 9
ln k versus P plots obtained for the spontaneous cis-to-trans isomerization of the iso-Ph and iso-cyano units either as free ligands or in their platinum complexes in acetonitrile solution (T = 63 °C for the iso-Ph and iso-cyano ligands, 60 °C for the [Pt(dppp)(iso-Ph)2]2+ complex, and 52 °C for the [Pt(dppp)(iso-cyano)2]2+ complex).
Scheme 2
Scheme 2
See this image and copyright information in PMC

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