Synthesis, structure, and properties of palladium(ii) complex of α-formyl pyrrolyl dipyrromethene

A simple alpha-formyl pyrrolyl dipyrromethene ligand was synthesized by deboronation of a BF2 complex of alpha-formyl pyrrolyl dipyrrin under Lewis acid catalyzed conditions. The alpha-formyl pyrrolyl dipyrrin ligand was treated with PdCl2 in CH3CN/Et3N at room temperature under inert atmosphere conditions for 3 h followed by recrystallization to afford a Pd(ii) complex of alpha-formyl pyrrolyl dipyrrin in 61% yield. The X-ray structure revealed that Pd(ii) was coordinated to three pyrrole Ns of the alpha-formyl pyrrolyl dipyrrin ligand and the fourth position was occupied by a water molecule with an overall distorted square planar geometry around the Pd(ii) ion. The formyl group present in the appended pyrrole ring was not involved in bonding with the Pd(ii) ion but helps in stabilizing the complex via hydrogen bonding interaction with the coordinated water molecule. The Pd(ii) complex was further characterized and studied thoroughly by 1D and 2D NMR, absorption, cyclic voltammetry and DFT/TD-DFT techniques. The absorption spectrum of the Pd(ii) complex showed one sharp intense band at 630 nm and less-intense bands at 585, 435 and 348 nm and the electrochemical studies indicated the electron-deficient nature of the Pd(ii) complex. The DFT/TD-DFT studies were in agreement with the experimental observations. The Pd(ii) complex was tested as a catalyst for the Suzuki-Miyaura coupling of aryl bromides with aryl boronic acid and the studies supported the catalyst's efficiency in the coupling reaction to form biaryl compounds.

Automated summary

A simple alpha-formyl pyrrolyl dipyrromethene ligand was synthesized and a Pd(ii) complex of the ligand was successfully prepared. The complex exhibited a distorted square planar geometry and was stabilized by hydrogen bonding with a coordinated water molecule. The complex showed strong absorption and electron-deficient nature. It also demonstrated good catalytic efficiency in the Suzuki-Miyaura coupling reaction.