Copper(I) and Silver(I) Complexes of 1,3-Diphosphacyclobutadiene Sandwich Anions: Synthesis, Crystal Structures, and Solution and Solid-State NMR Spectroscopic Characterization



1,3-Diphosphacyclobutadiene complexes have previously been employed as metalloligands to a few transition metals such as tungsten, cobalt, rhodium, platinum, and gold. Here, we describe the synthesis and the structural and spectroscopic characterization of novel copper(I) and silver(I) complexes with the sandwich anions [Co(η4-P2C2R2)2] (R = tBu or tPent). Reactions of [K(thf)3{Co(P2C2tPent2)2}] and [K(thf)2{Co(P2C2tBu2)2}] with CuCl(PPh3)/PPh3 yielded mononuclear copper(I) complexes [Cu{Co(P2C2R2)2}(PPh3)2] [R = tPent (1), tBu (2)]. The salt [Cu(PMe3)4][Co(P2C2tPent2)2] (3), which consists of a [Cu(PMe3)4]+ cation and a noncoordinated [Co(P2C2tPent2)2] anion, was obtained when [K(thf)3{Co(P2C2tPent2)2}] was treated with CuCl(PPh3) in the presence of an excess amount of PMe3. Salt metathesis of [K(thf)3{Co(P2C2tPent2)2}] with AgCl and AgSbF6 in the presence of PMe3 afforded novel silver(I) complexes [Ag{Co(P2C2tPent2)2}(PMe3)3] (4), [Ag{Co(P2C2tPent2)2}(PMe3)2] (5), and [Ag2{Co(P2C2tPent2)2}(PMe3)5]SbF6 (6). The molecular structures of 1, 2, 5, and 6 were determined by X-ray crystallography. The solution behavior of 16 was analyzed by variable-temperature 1H, 31P{1H}, and 13C{1H} NMR spectroscopy in [D8]THF. 31P solution and solid-state NMR spectra, aided by two-dimensional dipolar and/or J-based correlation spectroscopy, support the proposed structures and allowed the compositions of polycrystalline precipitated products to be analyzed. Furthermore, characteristic 31P chemical shifts and indirect spin–spin coupling constants offer a clear distinction between different bonding patterns realized in this class of compounds.