Synthesis and structural characterization of cis isomer of 1,2,3-triazol-5-ylidene based palladium complexes

•Structures of two cis isomers of 1,2,3-triazol-5-ylidene based Pd(II) chloride complexes are reported.•Activation barrier for syn–anti interconversion of the cis-Pd complex was obtained by VT-NMR.•Free energy of activation for syn–anti interconversion is 69.8 ± 0.1 kJ mol−1.

A palladium complex (3) of abnormal N-heterocyclic carbene (NHC) namely, 4-(hydroxymethyl)-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene was prepared via silver carbene transmetalation method and characterized by spectroscopic and single crystal XRD data. Single crystal analysis revealed the structure of the complex 3 to be a cis isomer. The synthesis of palladium complex 6via silver carbene transmetalation method led to a mixture of cis–trans isomers. In this case trans isomer was formed as major product. We have reported earlier the synthesis and structural characterization of trans isomer (trans-6). However, the presence of cis isomer was not recognized until the crude reaction mixture was recrystallized from acetonitrile. Pure cis isomer (cis-6) was obtained by washing the cis–trans mixture with acetonitrile followed by slow evaporation of acetonitrile solution at 35 °C. Structure of cis (cis-6) isomer was unambiguously established by single crystal XRD data.

Graphical abstractStructures of cis isomer of two new 1,2,3-triazol-5-ylidene based Pd(II) complexes are reported. The interconversion of syn–anti conformers of the cis-complex is studied by variable temperature NMR spectroscopy and the activation barrier is calculated.Figure optionsDownload full-size imageDownload as PowerPoint slide