Structural Diversity of Copper(I) Complexes Formed by Pyrrole- and Dipyrrolylmethane-Based Diphosphine Ligands with Cu–X···HN Hydrogen Bonds

Metal complexes containing hydrogen bond donor/acceptor groups are interesting because of their applications in several areas. In the course of our investigation on the synthesis of metal complexes using newly developed pyrrole-based diphosphine ligands, a few structurally interesting copper­(I) complexes containing the pyrrolic NH hydrogen bond donors were synthesized. The reaction of 2,5-bis­(diphenyl­phosphinomethyl)­pyrrole (PNP) with an equimolar quantity of CuX (X = Cl, Br, and I) afforded the binuclear copper­(I) complexes [Cu­(μ-X)­(μ-PNP-<i>P,P</i>)]₂ (<b>1–3)</b> in very good yields (87–90%). Conversely, the analogous reaction between 1,9-bis­(diphenyl­phosphino­methyl)­diphenyl­dipyrrolyl­methane (PNNP) and CuX (X = Cl, Br, and I) yielded the mononuclear Cu­(I) complexes [CuX­(PNNP-<i>P,P</i>)] (<b>4</b>–<b>6</b>) in very good yields (∼88%), in which the diphosphine ligand is chelated to the copper metal atom. Interestingly, when this reaction was carried out with a 1:2 mol ratio of ligand/metal, the cubane-like tetranuclear Cu­(I) complex, [Cu₄I₄{μ-Ph₂C­(C₄H₃N)₂-1,9-(CH₂PPh₂)₂-<i>P,P</i>}₂] <b>7</b>, was isolated in 68% yield. In addition, the reaction between the dipyrrolyl­diphosphine ligand (PNNP) and CuCl in the presence of 1 equiv of 1,10-phenanthroline monohydrate and NaBF₄ afforded a novel ionic binuclear mixed-ligand Cu­(I) complex, [Cu₂(μ-X)­(μ-PNNP-<i>P,P</i>)­(NN)₂]­BF₄ <b>8</b>, where NN = 1,10-phenanthroline in 57% yield. The structures of all these complexes were confirmed by the single-crystal X-ray diffraction method and are supported by spectroscopic data. In contrast to the PNP pincer ligand, the dipyrrolyl–diphosphine ligand (PNNP) adopts chelation as well as bridging coordination modes with Cu­(I) atoms, indicating its flexibility of bonding. In all the structures, the Cu–X···HN type of hydrogen bonds involving the metal halide ion as acceptor and the pyrrolic NH as donor are present with the Cu–X···H angles, which deviate from the favored 90°, as observed in their solid state structures. Further, the presence of this type of hydrogen bond was confirmed by NBO, AIM, and Hirshfeld analyses