N-Heterocyclic Carbene-Ag(I)-Phosphine Complexes: Comprehensive Synthesis, Characterization, and Bonding Analysis via Density Functional Theory

The substitution of a chloro ligand in (IPr)Ag–Cl with aliphatic and aromatic phosphine ligands, PPh3, PCy3, PPh2Py, dppf, dppm, and dppe, was investigated. Unlike gold(I) complexes, the heteroleptic complexes, [(IPr)Ag-PR3]+, are less stable in the solution phase. The order of mixing reactants, solvent type, and reaction time plays crucial roles in obtaining the desired product. In a methanolic solution, the generated [(IPr)Ag(I)]+ ions from (IPr)Ag–Cl are less stable compared with [(IPr)Au(I)]+ and only PCy3 and PPh2Py stabilize this cationic fragment in solution. In the single-crystal X-ray diffraction analysis of complexes 1 and 2, the Ag(I) centers exhibited a linear geometry. Other forms of silver(I) complexes containing only phosphine ligands were also formed in a solution containing the (IPr)Ag–Cl precursor. Computational analysis of the complexes using density functional methods provided insights into the nature of electronic transitions, noncovalent interactions, and fragmental bonding contributions.