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

Reaction of deprotonated 2,5-bis(2&#39;-pyridyl)pyrrole (HPDPH) with AgOTf (where OTf(-) = triflato) in THF readily yields a yellow triangular Ag3 complex [(PDPH)Ag]3 (1), of which the av. AgAg distance is 2.902 &#197;. A mixture of HPDPH and AgOTf reacts with PPh3 to afford a linear Ag3 complex [Ag{(PDPH)Ag(PPh3)}2](OTf) (2&#183;OTf), whereas it reacts with diethyl phosphite in the presence of Li[N(SiMe3)2] to yield a di-nuclear complex Li2[(PDPH)Ag2{P(O)(OEt)2}2](OTf) (Li2&#183;3&#183;OTf). In 2, the terminal Ag atoms are three coordinate containing one phosphorous atom from PPh3 and two nitrogen atoms of the PDPH ligand. The center Ag atom is only two coordinate, binding to the residued pyridyl N atom of the PDPH ligand. In 3, two silver atoms are bridged by one PDPH ligand. Treatment of PDPH with CuCl in the presence of NaH afforded a heterobimetallic copper-sodium complex [Cu(PDPH)2Na(thf)2] (4). The PDPH ligand in 1-4 is nonplanar, with torsion angles between pyridine and pyrrole rings in the range of 15.8-38.3&#176;. 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&#39;-bromo-2&#39;-pyridyl)pyrrole (HPDPBr) with AgOTf affords a di-nuclear complex [(HPDPBr)Ag]2(OTf)2 (5&#183;(OTf)2). Its HPDPBr 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 AgBr distances of 3.255-3.390 &#197; are observed.