Synthesis, Characterizations and Chemometric Analysis Approach of Nitrile Functionalized Asymmetrical Dinuclear Silver(I) Di-N¬-Heterocyclic Carbene Complexes

Abstract

A series of novel asymmetrical bis-benzimidazolium salts were synthesized via a two-step alkylation process, yielding the benzimidazolium salts of N,N'-(ethane/propane/butane-1,2/3/4-diyl)-1-benzylbenzimidazolium-1'-(n-benzonitrile)benzimidazolium dibromide (n = 2,3,4) (1Br – 9Br). These salts served as carbene precursors for the subsequent formation of nitrile-functionalized asymmetrical silver(I) di-NHC complexes (Ag1 – Ag9) (NHC = N-heterocyclic carbene) through an in-situ deprotonation method using Ag2O. Comprehensive characterization of the bis-benzimidazolium salts and their corresponding dinuclear silver(I) di-NHC complexes was performed using melting point determination, CHN elemental analyses, FTIR, and 1H- and 13C-NMR spectroscopy. The successful complexation of nitrile-functionalized NHC ligands with silver(I) ions was evidenced by the disappearance of the acidic-carbene proton peak (δ 9.69 – 10.23 ppm) in the 1H-NMR spectra of the complexes. Furthermore, the formation of Ag-Ccarbene bonds was confirmed by the appearance of characteristic peaks in the 13C-NMR spectra of Ag1 – Ag9 (δ 170.89 – 195.90 ppm). To elucidate structure-property relationships, the Principal Component Analysis (PCA) was applied to the NMR spectroscopic data. The PCA of the 1H-NMR data revealed distinct clustering of bis-benzimidazolium salts and their respective silver(I) di-NHC complexes, with the first two principal components accounting for 71.40% of the total variance. Similarly, the PCA of the 13C-NMR data explained 72.08% of the total variance through the first two principal components. These results demonstrate the efficacy of PCA in differentiating and classifying the compounds based on their structural features and functional groups. Moreover, this study highlights the synergistic application of advanced spectroscopic techniques and chemometric analysis in inorganic synthesis chemistry subject and the insights gained from this approach contribute to a deeper understanding of the structural properties and potential applications of these novel NHC complexes, paving the way for future developments in organometallic chemistry and catalysis.

Keywords

• N-heterocyclic carbene
• Silver(I) complexes
• Bis-benzimidazolium salts
• Nitrile-functionalization
• Principal component analysis