Multi-nuclear silver(i) and copper(i) complexes: a novel bonding mode for bispyridylpyrrolides

Abstract

Reaction of deprotonated 2,5-bis(2′-pyridyl)pyrrole (HPDP_H) with AgOTf (where OTf⁻ = triflato) in THF readily yields a yellow triangular Ag₃ complex [(PDP_H)Ag]₃ (1), of which the av. Ag⋯Ag distance is 2.902 Å. A mixture of HPDP_H and AgOTf reacts with PPh₃ to afford a linear Ag₃ complex [Ag{(PDP_H)Ag(PPh₃)}₂](OTf) (2·OTf), whereas it reacts with diethyl phosphite in the presence of Li[N(SiMe₃)₂] to yield a di-nuclear complex Li₂[(PDP_H)Ag₂{P(O)(OEt)₂}₂](OTf) (Li₂·3·OTf). In 2, the terminal Ag atoms are three coordinate containing one phosphorous atom from PPh₃ and two nitrogen atoms of the PDP_H ligand. The center Ag atom is only two coordinate, binding to the residued pyridyl N atom of the PDP_H ligand. In 3, two silver atoms are bridged by one PDP_H ligand. Treatment of PDP_H with CuCl in the presence of NaH afforded a heterobimetallic copper–sodium complex [Cu(PDP_H)₂Na(thf)₂] (4). The PDP_H ligand in 1–4 is nonplanar, with torsion angles between pyridine and pyrrole rings in the range of 15.8–38.3°. The argentophilic interactions, π⋯π stacking, and weak interaction of Ag⋯C(aromatic) are observed in these complexes. Interestingly, treatment of the analogous 2,5-bis(6′-bromo-2′-pyridyl)pyrrole (HPDP_Br) with AgOTf affords a di-nuclear complex [(HPDP_Br)Ag]₂(OTf)₂ (5·(OTf)₂). Its HPDP_Br ligands coordinate to Ag atoms in a head-to-head fashion, and two protonated pyrrole linkages reside in the anti-parallel direction and are non-coordinating. Short Ag⋯Br distances of 3.255–3.390 Å are observed.